Instead of using labels (e.g. to avoid unused_label) and because labels are most commonly used as the target of a goto. gdb also supports `break -probe foo:bar

Instead of using labels (e.g. to avoid unused_label) and because labels are most commonly used as the target of a goto. gdb also supports `break -probe foo:bar` when placing some `DTRACE_PROBE(foo, bar)` at the appropriate line. I think this is likely preferable to `break func:label` now.