Connect to target with OpenOCD, which will host a port we will connect to later with GDB.
Interfaces and Targets might live here if you installed OpenOCD via brew: (/usr/local/Cellar/open-ocd/0.11.0/share/openocd/scripts)
$ openocd -f interface/stlink.cfg -f target/stm32f0x.cfg
Open another terminal window, which will connect to the hosted port for debugging Note: port may be different, see output of above command
$ arm-none-eabi-gdb main.elf > target extended-remote :3333 > load
GDB Quick Guide https://beej.us/guide/bggdb/