How to debug RCARS4 using gdbserver?

This I found:
Enabling GDB per CPU
--------------------

In order to connect a GDB the CCI parameter `name.of.cpu.gdb_port` must be set a none zero value.

For instance
```bash
$ ./build/vp --gs_luafile conf.lua -p platform.cpu_1.gdb_port=1234
```
Will open a gdb server on port 1234, for `cpu_1`, and the virtual platform will wait for GDB to connect.

How the GDB is connected ?