Happy to help understand how the memconsole works, but I know nothing about kdb. Does it just call arbitrary functions, or do you have to define an explicit function to implement a new kdb command? Is there precedence of any other obscure drivers implementing their own commands? (Or did you mean kgdb instead?)

Note that if you only need this occasionally, you can also just dump the memconsole region manually (coreboot prints the address on boot, look for a line like "CONSOLE     2. 00000000f7fde000 00020000" near the end of ramstage output). You may need to manually figure out where it starts because it's a ring buffer, but it shouldn't be too hard to see.

I meant kdb, which is the text-based UI that you can enter commands in via just the serial port (don't need to hook up to kgdb).  The two things are a bit intermingled because when in kdb you can magially hook up gdb and also in gdb you can send kdb commands (using the "monitor" command in gdb).

...but yeah, I assume it's just a function call.  This is just on the back burner for me for now--I wanted to file it in my wishlist to keep track of it for when I had a moment to dig more.