Figure 2.5 shows the high level sequence diagram for GDB in response to the load command. This maps to the current target's to_load function, which in most cases will end up calling the current target's to_xfer_partial function once for each section of the image to load it into memory.

Figure 2.5.  Sequence diagram for the GDB load command

The load function will capture data from the loaded file, most importantly its start address for execution.