sys/ddb: Add hardware breakpoint support to ddb

[andrew]

Summary

As with hardware watchpoints add support for hardware breakpoints. The
command is only enabled on architectures that report support for them.
Currently no architectures do, however arm64 will add support in a
future change.

Sponsored by: Arm Ltd
Sponsored by: Innovate UK

[bz]

All your "stub functions" return (0), when in fact they probably should return an error? Or what happens if someone tries to set a (hw)breakpoint on these architectures?

[andrew]

In D22191#484972, @bz wrote:

All your "stub functions" return (0), when in fact they probably should return an error? Or what happens if someone tries to set a (hw)breakpoint on these architectures?

They are identical to the equivalent watchpoint functions, these also return 0 when not implementing hardware watchpoints.

[imp]

sys/arm/arm/db_trace.c

141

Shouldn't the stubs return failure?

[andrew]

sys/arm/arm/db_trace.c

141

I copied the hardware watchpoint stubs. These all return 0 when not implemented.

[andrew]

• Rebase
• Split out arm64 changes to new reviews
• Limit the hw breakpoint commands to architectures that support them

[jhb]

sys/ddb/db_break.c

299

You don't need the count for removing the breakpoint. The intention in DDB is that the count is the "skip count" similar to 'c 10' or the like in GDB.

[andrew]

sys/ddb/db_break.c

299

I've reworked the breakpoint handling code to support this correctly

[andrew]

Rebase on D44461

[andrew]

Add missing HAS_HW_BREAKPOINT check