On Thu, Jul 13, 2017 at 10:50:15AM +0200, Peter Zijlstra wrote: > On Thu, Jul 13, 2017 at 09:12:53AM +0200, Peter Zijlstra wrote: > > On Wed, Jul 12, 2017 at 05:32:25PM -0500, Josh Poimboeuf wrote: > > > If you want perf to be able to use ORC instead of DWARF for user space > > > binaries, that's not currently possible, though I don't see any > > > technical blockers for doing so. Perf would need to be taught to read > > > ORC data. > > > > So the problem with userspace stuff is that the unwind data isn't > > readily available from NMI context. > > > > So the kernel unwinder will trigger a fault and abort. > > > > The very best we can hope for is using the EH [*] stuff that all > > binaries actually have _and_ map. The only problem is that most programs > > don't actually use the EH stuff much so while its mapped, its not > > actually paged in, so we're still stuck. > > One gloriously ugly hack would be to delay the userspace unwind to > return-to-userspace, at which point we have a schedulable context and > can take faults. > > Of course, then you have to somehow identify this later unwind sample > with all relevant prior samples and stitch the whole thing back > together, but that should be doable. > > In fact, it would be at all hard to do, just queue a task_work from the
+not > NMI and have that do the EH based unwind.
