Figure 2.2 shows the sequence diagram for GDB start up.

Figure 2.2.  Sequence diagram for GDB start up

On start up, the GDB initialization function, gdb_init calls all the _initialize functions, including those for any architectures or remote targets.

Having initialized all the architectures, the first alphabetically is selected as the default architecture by initialize_current_architecture, and its initialization function, (by convention arch_gdbarch_init) is called.

Control returns to gdb_main, which sits in the command interpreter, waiting for commands to execute.