Disassembling large programs

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mlynn1974
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Disassembling large programs

Postby mlynn1974 » Thu Aug 24, 2017 11:20 pm

Hi,

Sorry if this has been asked before. I would like to disassemble the HitSquad version of Head Over Heels to allow keyboard controls and possibly redefinable keys so I don't have to play this with a joystick. I know using Steem I can play it with the joystick remapped to keys but I couldn''t do that on a real ST.

Anyway I tried disassembling it with Easy Rider 4 but it seems to output dc.b instead of the actual instructions for about half of the code.
This isn't caused by the code being encrypted as part of the copy protection because MonST can load it fine.

Easy Rider output:
TEXT
Begin:
DC.B 'H',$E7,$E0,$E0,'Hz',$00,$12
... continues until MOVE.L A7,$23680 much further down.

MonST output:
MOVEM.L D0-D2/A0-A2,-(A7)
... the first instruction is shown correctly.

Has anyone seen this problem before?

This doesn't seem to be problem because of MOVEM.L because a very simple program is disassembled correctly by Easy Rider 4:
MOVEM.L D0-D2/A0-A2,-(A7)
MOVEM.L (A7)+,D0-D2/A0-A2
CLR.W -(SP)
TRAP #1

On Windows 68kd.exe by Bart Trzynadlowski can disassemble Head Over Heels correctly, but its output isn't a format that can be easily loaded and re-assembled by GenST.
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Re: Disassembling large programs

Postby mikro » Fri Aug 25, 2017 2:45 am

I used TT Digger with much more success than Easy Rider. But it takes some time to get used to its UI. ;)

AtariZoll
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Re: Disassembling large programs

Postby AtariZoll » Fri Aug 25, 2017 7:09 am

I disassembled about 10 games and TOS 1.04 with Devpac 3. That can be pretty time consuming process - up to couple days for 1 SW.
It is just that MON can not determine is there some 68000 code or just data, so you must enter all data areas manually - and in some cases must give size too for it - for instance in case of address lists it must be l, and then it will set them as labels. In 1 case it appeared that there were too much data areas, more than can fit in MON input buffer, so I needed to split it in 2 parts, and then had extra job to combine 2 S files. As I tried, Easy Rider is nothing better.
However, I really don't see that you need to disasm. some game exec. for smaller changes. You can put your keyboard code to some safe space in RAM and adding just branch there from game. Then you will need Steem Debugger to trace down exact locs where input is read .
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Re: Disassembling large programs

Postby Mug UK » Fri Aug 25, 2017 8:29 am

Use the right-click mouse to toggle between opcode / data view layout. Select the area that you to change, then use the appropriate key combinations as below image.

EasyRiderExample.png


You can force disassemble a block of data back into code via the Ctrl & X option as well as reformatting the data display via the T key combination, e.g. data into neater lines of text with carriage returns displayed properly.

Also use the attached CONVERT.PRG (by Stew) which will convert an EasyRider disassembly into something a bit more compact (the bulk of spaces are converted to tabs, it's all put back into lower-case) and generally nicer to read through when you import it into GenST.
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