Re: [Xenomai-help] Handling Linux Signals in primary domain context

[Jan Kiszka <jan.kiszka@domain.hid>]

Gilles Chanteperdrix wrote:
> Jan Kiszka wrote:
>> Tschaeche IT-Services wrote:
>>> On Tue, Jun 01, 2010 at 04:32:37PM +0200, Philippe Gerum wrote:
>>>> Not in the absence of syscall. We thought about this once already, when
>>>> considering how a watchdog preempting a runaway task in primary mode
>>>> could force a secondary mode switch: there is no sane and easy solution
>>>> to this unfortunately.
>>> This is exactly Sigmatek's problem: Our customers develop code
>>> within our debugging/development environment. We want to catch
>>> this situation (the developer implements a while(1)) with a
>>> watchdog throwing SIGTRAP so that our debugger gets active
>>> and can locate the problem according to the stack frame...
>> CONFIG_XENO_OPT_WATCHDOG is probably what you are looking for. It tries
>> to catch "well-behaving" broken threads via SIGDEBUG and kills the
>> hopelessly broken rest - system alive again.
>>
>> You can then debug the former and need to do code review on the latter.
>> Or you could also try to add some loop-breaking Xenomai syscalls (or
>> even more clever checks) to library services the code under suspect
>> usually invokes.
> 
> I am afraid "well-behaving" means emitting syscalls. We have a radical
> way to cause a SIGSEGV to be sent to a thread having run amok: set its
> PC to an invalid address (after having printed the real PC). gdb will
> not be able to print where the program stopped, but should be able to
> print the backtrace.

Just discussing this with our customer raised spontaneous interest (due
to the yet unsolved switching issue with non-RT Xenomai threads). I'm
going to look into this, also trying to find some more sophisticated
approaches, e.g. simulating a call to preserve the call trace (which
would make it really useful) or jumping to some helper function that
issues a syscall.

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux