On Wed, Mar 23, 2016 at 06:13:49PM +0000, Will Deacon wrote: > > Will, why does it matter what the overflow handler is for this stuff? > > Because ptrace registers an overflow handler for raising a SIGTRAP and > ptrace users (e.g. GDB) expect to handle the single-stepping themselves. > Perf, on the other hand, will livelock if the kernel doesn't do the > stepping.
Ah makes sense. > FWIW, I hate this whole thing. The only users of the perf side just seem > to be people running whacky test cases and then pointing out the places > where we're not identical to x86 :( Yeah, its not my favourite part either. The whole breakpoint thing doesn't quite behave like a regular PMU so its all a bit 'special'.
