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Date: Mon, 23 Feb 2015 18:52:23 +0100
From: Jan Kiszka <jan.kiszka@siemens.com>
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Subject: Re: [Xenomai] ipipe: issues with ARM exception handling
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To: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>, Philippe Gerum <rpm@xenomai.org>
Cc: Xenomai <xenomai@xenomai.org>

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.

Jan


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