Hooking GDB to OpenOCD

OpenOCD implements the GDB remote protocol. Typically OpenOCD serves up a port on localhost, GDB then connects to this. In this arrangement there are two process involved in the debugging and they need to managed separately. This is a pain and tends led to scripts with pskill in them ¹.

It turn out that this isn’t the only way for GDB to communicate with the remote. The remote target can also be run as a child process.

target remote | openocd -p

By doing things this way we now only have one set of processes to manage (no more pskill).

Watchpoints

The Cortex M3 has hardware watch points in it’s onboard debugging unit (see Cortex M3 Specifications). OpenOCD and GDB both support watch points. Setting watch points using the watch command in GDB doesn’t seem to work. Setting the watch points in OpenOCD using monitor commands does seem to work.

monitor rwp [address] length

Watchpoints are removed with:

monitor rwp [address]

target remote | openocd -p
set remote hardware-breakpoint-limit 6
set remote hardware-watchpoint-limit 4
monitor reset halt