Standalone gdb server?

Has anyone encountered a standalone gdb server? That is gdb server that runs on a bare metal.

I've been looking for sources to build one. Doesn't need to be ARM, but that might help.

Maybe someone has come across a document explaining how gdb server really works?

(It might help in reading the 'standard' gdb server code.)

I understand that 'stub' means "gdb server" linked into the executable, but I'd like to have a server with which I could upload programs onto the board for debugging through the network or serial IF.

My main concern is attaching to the program to be debugged, when there is no OS (and no processes).

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