Re: [Xenomai] ipipe: issues with ARM exception handling

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2015-02-23 18:52, Jan Kiszka wrote:
> On 2015-02-23 18:49, Jan Kiszka wrote:
>> On 2015-02-23 18:38, Jan Kiszka wrote:
>>> On 2015-02-23 18:14, Gilles Chanteperdrix wrote:
>>>> entry.S does not handle virtual irq state. So, if it returns to
>>>> user-space with the root stage stalled, nothing will unstall it. And
>>>> you probably get a lockup.
>>>
>>> Right, that's a point. I'm seeing this pattern in x86 now as well.
>>> Comparing further.
>>>
>>> What's missing on ARM are flags adjustments in the register set before
>>> letting Linux inspect that (__fixup_if equivalent). And we should
>>> probably use ipipe_restore_root_nosync on return.
>>
>> There is another difference that should be considered carefullly. x86 says
>>
>>  * If we fault over the root domain, we need to replicate the
>>  * hw interrupt state into the virtual mask before calling the
>>  * I-pipe event handler.
>>
>> and then updates the root state before it calls __ipipe_notify_trap -
>> why? x86-specific?
> 
> The why is referring to the "before calling the I-pipe event handler" -
> that we have to do this afterwards when we ended up or already were in
> root is clear.

It seems this is now - at beast - historic logic of x86. We (no longer?)
report anything when __ipipe_notify_trap is invoked over the root domain:

        /*
         * We send a notification about all traps raised over a
         * registered head domain only.
         */
        if (__ipipe_root_p)
                goto out;

Will clean up on x86 soon.

Jan

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