Hi Joscha,
the 'gdb_monitor.run' script should work out of the box on foc_x86_32, nova_x86_32 and (with one failing test) foc_pbxa9 on Qemu. I tried it with your github branch and it worked for me after I removed the newly added TCP redirection line from the run script.
The 'gdb_monitor_interactive_tcp.run' script works for me on these platforms on Qemu with the attached patch.
For the HW platform, there might be some work to do on the base system if there are problems with pausing and resuming of threads or with getting the current register state. When trying to resume execution at a specific instruction pointer or to modify register contents in general, the base platform must support this. I'm not sure if the HW platform already supports it (base-foc does, base-nova not yet).
Regards, Christian