Genode 16.05 Fault handler

Wed Aug 31 14:24:33 CEST 2016

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?

[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
>>>>>>
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