[Xenomai-help] Powerpc alignment exception

[Makarand Pradhan <makarandpradhan@domain.hid>]

Hi,

There has been a thread on this topic in the past:

https://mail.gna.org/public/xenomai-help/2009-08/msg00023.html

A quick background: We get the alignment exception, as we pass 
-fpack-struct option to gcc and some data in structures is misaligned.

I have been testing the patch on Linux 3.0.0, Xenomai 2.6 and it seems 
to work well. Do you think, it requires any additional changes to be 
used with Xenomai 2.6?

Also, I am trying to understand how it works and have a question. Am 
summarizing my understanding below. Would appreciate your comments:

alignment_exception:

+     if (test_bit(IPIPE_NOSTACK_FLAG, &ipipe_this_cpudom_var(status)) &&
+         ipipe_trap_notify(IPIPE_TRAP_ALIGNMENT, regs))
               return;

I believe, the IPIPE_NOSTACK_FLAG is set when we are running in Linux. 
So we should invoke ipipe_trap_notify only while we are running in 
linux.  While running in the primary domain, we would go ahead and fix 
the alignment.


+     if (!ipipe_root_domain_p &&
+         ipipe_trap_notify(IPIPE_TRAP_ALIGNMENT, regs))
+             return;
+
I am not able to figure this part properly. If we are not in the root 
domain we invoke ipipe_trap_notify. (I believe root domain = Linux). So 
if we are in the primary, we would invoke ipipe_trap_notify. 
ipipe_trap_notify in turn would invoke the event handler 
(xnpod_trap_fault). This would send us to the secondary domain. All the 
same, we stay int he primary as per my tests. So, I am making a mistake 
somewhere. Would appreciate your opinion.

Rgds,
Makarand.




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