Genode 16.05 Fault handler

Wed Aug 31 18:23:36 CEST 2016

Hi Denis,

On 08/31/2016 02:24 PM, Denis Huber wrote:
> Hello Sebastian,
> 
> thank you for the working solution :)
> 
> Now the page faults of threads other than the main-thread can be 
> handled. What about the main-thread? How can I change the example to be 
> able to handle page faults from the main-thread?
> 
> Do I have to create an extra thread which is dedicated to handle page 
> faults of the other threads like the old Signal_receiver/Signal_context 
> approach [1]? I thought the new design of the Entrypoint provides this 
> feature (Entrypoint handles page faults in its thread). Or is my 
> understanding wrong?

as I said yesterday, a thread (what an EP essentially is) cannot handle
its own page fault. It is a hen and egg problem. Microkernels just save
the thread state and call a pager thread in order to resolve the page
fault. Note, that this thread does not have to be within the same
program (or protection domain). What I don't understand, why would you
want a self paging program? The memory has to be provided and paged from
the outside anyway (in Genode that would be the parent or core)?

Cheers,

Sebastian

> 
> [1] 
> https://github.com/702nADOS/genode-CheckpointRestore-SharedMemory/blob/7c1c6183a5132aa67d2604221d4eb6ee39106c64/src/test/fault_handler_old/main.cc
> 
> 
> Kind regards,
> Denis
> 
> On 30.08.2016 18:36, Sebastian Sumpf wrote:
>> Hi Denis,
>>
>> On 08/30/2016 04:21 PM, Denis Huber wrote:
>>> Hello Sebastian,
>>>
>>> I created a new thread which causes the page fault, and also assigned an
>>> extra Entrypoint for the Signal_handler [1], but still no success.
>>> Perhaps I am using the Signal_handler in a wrong way.
>>>
>>> [1]
>>> https://github.com/702nADOS/genode-CheckpointRestore-SharedMemory/blob/c58b4144bff720f837112c590ebd2148e9c3f199/src/test/fault_handler/main.cc
>>>
>>
>> You are mixing some things up here, I pushed a working version of your
>> code (tested on Fisco.OC in Qemu) to GitHub:
>>
>> https://github.com/ssumpf/genode/commit/0075a0026faa8079f03dfb4d43ec281ef51f1083
>>
>> I hope this clarifies things a little. The relevant output should look
>> like this:
>>
>>> [init -> pf-signal_handler] --- pf-signal_handler started ---
>>> no RM attachment (WRITE pf_addr=1000 pf_ip=10001d9 from 2d2000)
>>> Warning: could not resolve pf=0x1000 ip=0x10001d9
>>> [init -> pf-signal_handler]   Region map state is WRITE_FAULT pf_addr=0x1000
>>> [init -> pf-signal_handler]   Allocating dataspace and attaching it to the region map
>>> [init -> pf-signal_handler] --- pf-signal_handler ended ---
>>
>> Sebastian
>>
>> P.S. As I see it, you needed the 'join' because the thread was created
>> on the stack again ;) One has to use the heap or bss/data.
>>
>>
>>> Kinds regards,
>>> Denis
>>>
>>> On 30.08.2016 15:45, Sebastian Sumpf wrote:
>>>> Hello again,
>>>>
>>>> I missed that part
>>>>
>>>>> *((unsigned int*)0x1000) = 1;
>>>>
>>>> in my last reply. You cannot cause a page fault in your entry point and
>>>> also handle it in the entry point thread, because the entry point is not
>>>> able to receive signals when it is in page fault. It is a hen and egg
>>>> problem.
>>>>
>>>> If you cause the fault from another Genode thread, it should work as
>>>> expected.
>>>>
>>>> Sebastian
>>>>
>>>>
>>>> On 08/30/2016 03:07 PM, Denis Huber wrote:
>>>>> Hello Sebastian,
>>>>>
>>>>> I moved sigh to the member attributes [1], but without success. I also
>>>>> tried to use a heap to store the Signal_handler, also without success.
>>>>>
>>>>> [1]
>>>>> https://github.com/702nADOS/genode-CheckpointRestore-SharedMemory/blob/93eaec436ce9b6d3b3a6663558bff9af925ae70f/src/test/fault_handler/main.cc#L19
>>>>>
>>>>> I am using run script [2], if it helps.
>>>>>
>>>>> [2]
>>>>> https://github.com/702nADOS/genode-CheckpointRestore-SharedMemory/blob/93eaec436ce9b6d3b3a6663558bff9af925ae70f/run/fault_handler.run
>>>>>
>>>>>
>>>>> Kind regards,
>>>>> Denis
>>>>>
>>>>> On 30.08.2016 14:36, Sebastian Sumpf wrote:
>>>>>> Hi Denis,
>>>>>>
>>>>>>> Signal_handler<Main> sigh = {env.ep(), *this, &Main::_handle_fault};
>>>>>>
>>>>>> The line above, creates the Signal_handler on the stack and destructs
>>>>>> this handler as soon as the 'Main' constructor is finished.
>>>>>>
>>>>>> Therefore, 'sigh' should be a member of the 'Main' class.
>>>>>>
>>>>>> Regards,
>>>>>>
>>>>>> Sebastian
>>>>>>
>>>>>> On 08/30/2016 02:10 PM, Denis Huber wrote:
>>>>>>> Dear Genode community,
>>>>>>>
>>>>>>> in Genode 16.05 the old usage of Signal_receivers and Signal_contexts is
>>>>>>> considered deprecated. Instead Signal_handler and Signal_transmitter
>>>>>>> shall be used.
>>>>>>>
>>>>>>> I am trying to use a Signal_handler as a fault handler for env's address
>>>>>>> space. I wrote a short test to illustrate the problem [1].
>>>>>>>
>>>>>>> [1]
>>>>>>> https://github.com/702nADOS/genode-CheckpointRestore-SharedMemory/blob/c9a5a1f999a2ce1c6ffd5c316eee127c93d87308/src/test/fault_handler/main.cc
>>>>>>>
>>>>>>> The output of [1] is as follows:
>>>>>>> "
>>>>>>> [init -> pf-signal_handler] --- pf-signal_handler started ---
>>>>>>> no RM attachment (WRITE pf_addr=1000 pf_ip=100061c from 2ae000)
>>>>>>> Genode::Pager_entrypoint::entry()::<lambda(Genode::Pager_object*)>:
>>>>>>> Could not resolve pf=1000 ip=100061c
>>>>>>> "
>>>>>>>
>>>>>>> The signal handler was registered correctly, because the line
>>>>>>> "
>>>>>>> Genode::Core_pd_session_component::submit(Genode::Capability<Genode::Signal_context>,
>>>>>>> unsigned int)::<lambda(Genode::Signal_context_component*)>: invalid
>>>>>>> signal-context capability
>>>>>>> "
>>>>>>> is missing. However, the method _handle_fault() is never entered. What
>>>>>>> am I doing wrong?
>>>>>>>
>>>>>>>
>>>>>>> Kind regards,
>>>>>>> Denis
>>>>>>>
>>>>>>> ------------------------------------------------------------------------------
>>>>>>> _______________________________________________
>>>>>>> genode-main mailing list
>>>>>>> genode-main at lists.sourceforge.net
>>>>>>> https://lists.sourceforge.net/lists/listinfo/genode-main
>>>>>>>
>>>>>>
>>>>>>
>>>>>> ------------------------------------------------------------------------------
>>>>>> _______________________________________________
>>>>>> genode-main mailing list
>>>>>> genode-main at lists.sourceforge.net
>>>>>> https://lists.sourceforge.net/lists/listinfo/genode-main
>>>>>>
>>>>>
>>>>> ------------------------------------------------------------------------------
>>>>> _______________________________________________
>>>>> genode-main mailing list
>>>>> genode-main at lists.sourceforge.net
>>>>> https://lists.sourceforge.net/lists/listinfo/genode-main
>>>>>
>>>>
>>>>
>>>> ------------------------------------------------------------------------------
>>>> _______________________________________________
>>>> genode-main mailing list
>>>> genode-main at lists.sourceforge.net
>>>> https://lists.sourceforge.net/lists/listinfo/genode-main
>>>>
>>>
>>> ------------------------------------------------------------------------------
>>> _______________________________________________
>>> genode-main mailing list
>>> genode-main at lists.sourceforge.net
>>> https://lists.sourceforge.net/lists/listinfo/genode-main
>>>
>>
>>
>> ------------------------------------------------------------------------------
>> _______________________________________________
>> genode-main mailing list
>> genode-main at lists.sourceforge.net
>> https://lists.sourceforge.net/lists/listinfo/genode-main
>>
> 
> ------------------------------------------------------------------------------
> _______________________________________________
> genode-main mailing list
> genode-main at lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/genode-main
> 