Fixing Classic BRAT cracktro for more than 512k chip

[Hewitson]

Hi guys,

I thought trying to fix a small problem with one of my favourite intros would be a good learning experience. With 1mb chip, the scroller becomes invisible for about 50% of the time.

If anyone could give me some tips on why this is happening and the best way to go about fixing it, they'd be very greatly appreciated!

I have attempted to decrunch it with XFDDecrunch but it results in an unexecutable file, which when disassembled crashes the Amiga when I try to reassemble it.

Disassembling the original packed executable and reassembling it works perfectly.

It can be downloaded from here if anyone would be willing to take a quick look at it for me: http://ftp.amigascne.org/pub/amiga/G...Classic-CrBrat

I have also uploaded the disassembly of both the crunched and decrunched executables to the zone.

Thanks in advance

[Hewitson]

I'm pleased to report I've made some slight progress, adding the option "LP" to xfddecrunch resulted in a decrunched executable that works perfectly.

Unfortunately trying to disassemble this with IRA says "Hunk: 0000fffe - Not Supported" and quits.

I get the same error with the addresses "00000130 48E7FFFE" from D68k.

[BippyM]

All that line is doing is the following and there are only 2 instances of this within the code.

Movem.l d0-d7/a0-a6,-(a7)

[pmc]

Morning Hewitson

I had a quick look at the two disassemblies.

If you look at the crunched version, what you're seeing is the disassembled decrunch header for the Defjam packer that was used to crunch the cracktro. The data in that file is the crunched cracktro that gets decrunched by the header.

What you can see in the decrunch code is a jmp ext_0000. Which translates as, from looking at the equates, to jmp $48000. This is the absolute address in memory that the cracktro is decrunched to. Ideally you want to make the code relocatable again.

What you could try doing is disassembling the uncrunched executable but setting the origin (this is a Resource disassembler term, sorry I've never used IRA) for the code as $48000. That would then let the disassembler work out how to offset all the branches in the code to the correct places as relative offsets.

If you then add a: section cracktro,code_c to the very top of the code and then try running it you might find it works OK.

I used this exact same method when I disassembled Phenomena's Flight Of Dreams II demo and managed to get it to run OK as a relocatable reassembled executable.

Hope that helps

[Hewitson]

I gave IRA the -OFFSET=$48000 option and the code now reassembles and runs perfectly! However all this does is add an ".ORG $48000" to the start of the source. I commented this out and the intro still ran fine but the music was very high pitched for some reason.

I'd like to use Resource so I can do exactly as you suggested. I set the origin to $48000 and disassembled and it has hundreds of question marks in it! eg:

btst ????$14,a2

How can I get it to produce a usable disassembly?

Thanks

[pmc]

Originally Posted by Hewitson

I gave IRA the -OFFSET=$48000 option and the code now reassembles and runs perfectly!

\o/

Originally Posted by Hewitson

However all this does is add an ".ORG $48000"

org is just a way of getting the assembler to set the code to be run from an absolute location.

Originally Posted by Hewitson

How can I get it to produce a usable disassembly?

I don't have huge experience with Resource so maybe someone else here can give a better answer but in my limited experience, you sometimes have to set sections of the disassembly as code or data and re run the disassemble option.

Not a very techincal or detailed desciption that I'm afraid. Someone else here will be able to elaborate I'm sure.

[StingRay]

Originally Posted by pmc

If you then add a: section cracktro,code_c to the very top of the code and then try running it you might find it works OK.

I used this exact same method when I disassembled Phenomena's Flight Of Dreams II demo and managed to get it to run OK as a relocatable reassembled executable.

Flight of Dreams II works that way because all necessary buffers etc. were allocated in the executable, i.e. there was no reason to let it run at an absolute address at all.

In this case however screens etc are located at absolute addresses ($70000 etc) so you can't just add a "SECTION CODE,CODE_c" and hope for the best. In the best case it might run by luck, in the worst case your code has been loaded to the screenmem area and what happens then should be obvious.

Originally Posted by Hewitson

I gave IRA the -OFFSET=$48000 option and the code now reassembles and runs perfectly! However all this does is add an ".ORG $48000" to the start of the source. I commented this out and the intro still ran fine but the music was very high pitched for some reason.

The module needs to be at $50000, if you remove the ORG $48000 the module is not at $50000 any longer and thus it won't be played correctly.

Originally Posted by Hewitson

I'd like to use Resource so I can do exactly as you suggested. I set the origin to $48000 and disassembled and it has hundreds of question marks in it! eg:

btst ????$14,a2

That ReSource complains is correct since btst is byte only when the destination is a memory address.

Anyway, you can check this thread, I explained how to disassemble absolute address code there.

However, this is no beginner's stuff in my opinion, learn to walk before you try to run!

[pmc]

OK thanks Stinger.

As I say, I have no great experience at this stuff.

Hewitson: best bow to Stinger's superior knowledge in my opinion.

[Hewitson]

Well, stuff trying to make it relocatable. I'd rather put up with it crashing the system every time I exit it than get as frustrated as I am right now.

I would absolutely love to fix the issue with the scroller though.

Originally Posted by StingRay

That ReSource complains is correct since btst is byte only when the destination is a memory address.

Fair enough.

Originally Posted by StingRay

However, this is no beginner's stuff in my opinion, learn to walk before you try to run!

Jumping in at the deep end is how I learn best

[BippyM]

Fix it using WHDload