From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <44422292.6040205@domain.hid> Date: Sun, 16 Apr 2006 12:55:14 +0200 From: Philippe Gerum MIME-Version: 1.0 Subject: Re: [Adeos-main] Re: [Xenomai-core] kgdb over ipipe References: <44377F75.9030707@domain.hid> <4438FAFA.3020105@domain.hid> <44397CBF.905@domain.hid> <443C0A34.70107@domain.hid> <443C0F80.7070600@domain.hid> <443C20D4.1090801@domain.hid> In-Reply-To: <443C20D4.1090801@domain.hid> Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit List-Id: "Xenomai life and development \(bug reports, patches, discussions\)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jan Kiszka Cc: adeos-main@gna.org, xenomai-core Jan Kiszka wrote: > Philippe Gerum wrote: > >>Jan Kiszka wrote: >> >>>Philippe Gerum wrote: >>> >>> >>>>Jan Kiszka wrote: >>>> >>>> >>>>>Jan Kiszka wrote: >>>>> >>>>> >>>>> >>>>>>Hi, >>>>>> >>>>>>this is the preliminary, though already usable result of my recent >>>>>>effort to extend the tool situation for Xenomai: A kgdb patch >>>>>>series for >>>>>>2.6.15 on x86. It already works quite well but likely does not yet >>>>>>catch >>>>>>all fatal scenarios (e.g. page faults in the Xenomai domain). >>>>>> >>>>> >>>>> >>>>>And here comes another revision (prepare patch remains unmodified). >>>>> >>>>>It gets closer to what Philippe also just suggested in the original >>>>>thread: hook KGDB into I-pipe in favour of registering a dedicated >>>>>domain. The latter approach modifies the I-pipe state in a way which >>>>>may >>>>>blur the picture of I-pipe itself to the debugger. This revision hooks >>>>>exception events into the I-pipe core so that they are delivered the >>>>>normal way when the root domain is active, but get catched early for >>>>>higher domains like Xenomai. I'm just not sure about the best way to >>>>>handle the serial line IRQ. Philippe, do you see problems with current >>>>>approach? Should we better hook into __ipipe_handle_irq (which would >>>>>make things more complicated, I'm afraid)? >>>>> >>>> >>>>The current approach works fine unless a runaway thread goes wild with >>>>interrupts disabled (i.e. stall bit set) in the root stage or in any >>>>higher priority domain regardless of the root domain state, in which >>>>case the serial IRQ won't make it through the pipeline to KGDB. >>> >>> >>>But catching this would mean to change the behaviour of ipipe regarding >>>the highest priority domain from hard to soft masking of IRQs. Hmm, >>>should be made at least optional to catch scenarios where this change >>>makes bugs move (away...). >>> >>>Would be the easiest way to achieve this to register a dummy domain >>>ahead of Xenomai (i.e. with higher prio)? >> >>This would be the theoretically "normal" way to do this, but this comes >>with the undesirable side-effect of losing the hw masking of interrupts >>for the Xenomai domain, since you stack another domain on top. >> >> Additionally, we would have to >> >>>modify the IRQ pipeline in a way that, e.g., some flag makes an IRQ not >>>only sticky but also "non-maskable" (I would make this also an option to >>>avoid overhead for non-debugging scenarios). >>> >> >>By non-maskable, you mean at PIC-level? > > > Nope, at software-level. I mean that such IRQs would always be passed > down the pipeline, even through stalled domains. > Can't do that. This would wreck the entire Adeos logic. > >>>Well, not yet an essential feature for me, because we still have the NMI >>>watchdog and the option to spread breakpoints. But we should keep it in >>>mind. >>> >>> >>> >>>>>In contrast to the first version, exceptions happening in the Xenomai >>>>>domain now also get reported to KGDB. Debugging mostly works fine, I'm >>>>>just facing unknown problems with intercepting and then continuing >>>>>kernel-only RT threads. KGDB sometimes reports "E22" back in this case, >>>>>but always locks up. Maybe it gets confused by the fact the there is no >>>>>Linux task behind Xenomai kernel threads? I tested this by putting a >>>>>breakpoint into xnpod_suspend_thread and running latency in mode 0 and >>>>>1. 0 works fine, 1 not. >>>>> >>>> >>>>KGDB is relying on "current", so it's reading garbage over Xenomai's >>>>kernel threads. >>>> >>> >>> >>>Attached is an improved version of the kgdb-ipipe.patch that copes with >>>this situation by mapping invalid currents to init_task. Kernel threads >>>are nicely debuggable now. =8) >>> >> >>Ok, queued. >> > > > As an add-on patch like the tracer? > Don't know yet. The bottom line is that changes which are independent from the KGDB patch could go to the mainline Adeos patch since they are few and small, except for entirely new files which would be maintained separately. -- Philippe.