kdp_poll: no debugger device with two-machine debugger

Question

I have to use firewire as my kernel extension loads before the target has an IP address.

My kernel extension calls PE_enter_debugger() in its start routine.

I see "waiting for debugger" twice, then just once the console says "kdp_poll: no debugger device".

I would think that means the nvram boot-args is wrong but I've followed the instructions:

debug=0x814e kcsuffix=development kdp_match_name=firewire fwkdp=0x8000

The host is a late 2012 Mac Mini, macOS 10.12.4 build 16E195.

The target is a mid 2010 Mac Pro with the same macOS build.

My kernel debug kit matches the macOS build.

Google yields no joy. Have you a clue for me?

Answer 1

The 2010 Mac Pro has built-in Firewire ports and no Thunderbolt, so I think your problem might be the fwkdp=0x8000 setting. As far as I'm aware, you only want to set that if you're debugging through a Thunderbolt-Firewire adapter (or Thunderbolt display's or dock's Firewire port) on the target machine side.

(Sorry, only just seen your question as I have alerts on the 'xnu' and 'kext' tags but 'kernel' and 'osx' are too noisy.)