Seems like the if error / goto fail can be extract from the individual switch cases and moved after the switch.

That’s the expected behavior by clients if functionality isn’t implemented? (As opposed to an explicit error?)

Do errnos make reasonable values here? I forget what tx_err does.

It doesn’t matter that the type may not match the breakpoint at addr?

Yes. It's the same as the default case for the big switch in gdb_trap().

Yep, it's meant to send an errno.

At the moment, no. Our hw debug implementations don't look at this when they select which watchpoint to remove (some don't even look at length).