Anyone here handy with a disassembler like IDA Pro?

[Kai Robinson]

Specifically, i'm trying to run Macintosh ROM's through it.

While it can decode snippets of functions - it dumps a lot of 'data' it thinks - it can't determine what's code and what's not. Also, the references, while they line up, seem to be scattered around, and the visual graph looks like spaghetti. I'm pretty sure the first 4 bytes of the ROM are a checksum, as per https://www.bigmessowires.com/2016/06/10/rom-hacking-tutorial-with-rom-inator-ii/ with the base address being 0x0 - but i'm a bit lost here. I can spend all day expanding 'unknown' chunks into code, but whether that's actually supposed to BE code or if it's just trying to turn something irrelevant INTO code.

 

[cy384]

The first four bytes are a checksum, the next four bytes contain the address to start execution. So that's the address to start decoding at. Unfortunately there's tons of data mixed into the ROM, a full disassembly will take a lot of work. I used Ghidra a little to help with my ROM hacks. The process was basically: start at something that seems correct, try to disassemble a little more, undo when it gets funky, mark stuff that seems like data, repeat until satisfied/bored.

 

[cy384]

So while I was doing some other stuff I found out that Apple published a bunch of ROM map files with MPW, which have the addresses in ROM for a bunch of stuff, for all(?) 68k Mac ROMs. I converted them into a format that Ghidra can import, and some quick instructions, you can find them here on github. I am fairly confident it works and these are being loaded correctly. It's really only a starting point, but at least you get a bunch of labels to work with.

Also I know fdisasm has some partial disassembly for several Macs.

Ghidra screenshot of a Mac SE ROM with the labels: