Messages in this thread | | | Date | Tue, 19 Jan 2010 17:21:02 +0100 | From | Frederic Weisbecker <> | Subject | Re: HW breakpoints perf_events request |
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On Tue, Jan 19, 2010 at 10:12:10AM -0500, Frank Ch. Eigler wrote: > Hi - > > > > > [...] > > > > What about extending ptrace to support a new type of > > > > breakpoint debugging interface? > > > > > > This is the sort of reason why the utrace-gdbstub prototype was > > > constructed. It should allow in-kernel implementation of the > > > multithreaded gdb extensions. (By the way, it can already use uprobes > > > rather than userspace-managed breakpoints.) > > > > Can utrace somehow meet Joshua's needs? > > Not directly, I'm afraid. I jumped in at a late stage of the thread > that got a bit away from Joshua's original note > (http://lkml.org/lkml/2010/1/13/490). OTOH, it could be made to work > a few different ways. > > One is a systemtap or hand-written module that maps selected > perf-event hits in the kernel to an application SIGTRAP.
Yeah would work.
But I rather hope we can extend ptrace interface to handle such new needs instead (ie: having a more scalable breakpoint interface support by ptrace).
> Another is using the gdbstub, extended with gdb watchpoint support (Z* > packets), which would tie into the hw-breakpoint system directly. > Joshua's application would manage the debug registers by means of a > userspace supervisor process sending the appropriate Z* packets to the > gdbstub, and otherwise letting the program run. When a watchpoint > fires, the supervisor process can instruct gdbstub to send a SIGTRAP > to the application. In this scenario, the perf syscall / subsystem is > not used at all.
Is this gdbstub an interface to utrace?
This: http://lwn.net/Articles/364268/ ?
> > > I'm not sure what kind of interface it can offer for that. The fact > > is I don't know very well utrace :) > > That's ok. utrace is an in-kernel API for process management. ptrace > and the RFC gdbstub are two possible userspace interfaces tuned for > third-party debugging.
Ok.
> > > Do you plan a resubmission soon? > > Utrace core has been resubmitted at the end of December > (http://lkml.org/lkml/2009/12/17/466), with no further comments > received.
Hmm, there has been deep review from Peter, IIRC.
> I hope it gets plopped into linux-next ASAP and merged next > time. The gdbstub was an RFC only at this stage, but if other people > get excited about it, we're happy to spiff it up for proposed merging.
Ok.
Thanks.
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