For a long time Intel has offered a “freeware” (not open source) solution to debug UEFI with a 2-system solution, one running either Linux/GDB or Windows/Windbg:
Last updated in 2017, it used to work on the old TunnelMountain desktop systems, I’ve been meaning to see if it works on MinnowBoard2 systems. And this is Intel-centric (and I presume it may also work on AMD), but, I’m not aware of ARM — nor UEFI Forum’s Tianocore — having a similar offering, which I’d like to be able to use on a UEFI-based Rasberry Pi. HOWEVER… I just noticed this, which came out LAST YEAR, somehow I missed it, an open source solution!!
This is a open code replacement for Intel’s binary only GDB server that comes as part of the ‘Intel UEFI Development Kit Debugger Tool’. Since that tool is Intel x86/64 Linux/Windows only this allows more flexibility. E.g. you can run this on any ARM based SoC with python3 and a USB OTG port connected directly to your target via a USB2.0 EHCI Debug port using the Linux USB OTG Debug Port gadget. You can then connect to that target remotely from your build box, etc. This also allows you to tweak the debugger itself. I’ve already added some additional functionality here to assist when using SourceLevelDebugPkg on non-EDK2 (i.e. no source available) firmwares such as AMI Aptio IV.
Now it just needs also add LLDB support (especially for the Clang-centric HBFA branch)… 🙂 Given this is open source, unlike the Intel solution, this is a possiblity!