GBDK calling convention

[qwertymodo]

I've run into a few homebrew ROMs that were obviously written in C. GBDK seems to be the only game in town when it comes to C compilers that target the GB, so I'm guessing that's what was used. Here's what I was able to find about the C calling convention in GBDK: http://gbdk.sourceforge.net/doc/html/c0402.html

From the looks of things, this would be implemented in the .cspec file. I've found the documentation for the cspec format, but it's a lot to work through. I tried copying/pasting the _stdcall convention from Ghidra's included z80 cspec, and then modifying it to remove the register inputs, change the alignment to 1, change the output register to DE, and remove some of the unaffected register nodes (not really sure about that last part). Seems to be a decent starting point.