@sebastian-roth I appreciate your help, and that does answer my question. For the record, though, the problem remains. Building from source using the fog provided (GitHub dev-branch pulled) console.h, general.h, and settings.h gives the same failure in hyper-v. Building from source, and only including ipxescript (not replacing the 3 files above) results in a undionly.kpxe that does work past initializing devices in hyper-v. I’m going through each option now to try to narrow it down as it seems now something in the config is what is tripping up hyper-v.
Edit: Modified the default ipxe general.h file to include param_cmd, and changed nothing else. Completed downloading an image to my vm on hyper-v. Unsure what I broke in the process, as there are a lot of switches I’m missing, but I can confirm this works on my setup.