Re: [Xenomai-help] SH4 port

[Jan Kiszka <jan.kiszka@domain.hid>]

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Kiichi Kameda wrote:
>> [ksrc/arch/sh/switch.c]
>>
>> void rthal_switch_to(xnarchtcb_t *prev, xnarchtcb_t *next)
>> {
>> ...
>>         /*
>>          * Restore the kernel mode register
>>          *      k7 (r7_bank1)
>>          */
>>  if(next->user_task) {
>>
>>             asm volatile("ldc       %0, r5_bank"
>>                      : /* no output */
>>                      : "r" (next->user_task->thread_info));
>>  }
>>
>> Is there a particular reason why comment and reality diverge regarding
>> the thread_info register? Could this cause your troubles?
>>
> 
> I'm sorry, the comment is wrong.
> The code that uses r7_bank  results in overwriting "current".

What code is it?

> To avoid this,  I changed  from r7_bank to r5_bank for Xenomai context
> switch .

Wouldn't it be better to avoid that overwriting in the first place
instead of escaping from it? You may not be safe from code running on
behalf of a Xenomai user-space thread that assumes current is still in
r7_bank.

> Also, I added to the Linux context switch code  so that thread_info is set
> in r5_bank register  as well as in r7_bank regsiter.
> r5_bank register is referenced in the page fault handling code.

The handling code of Xenomai or Linux?

The goal must be that the environment for a shadowed Xenomai thread
looks (almost) like that of a normal Linux thread. If there is Xenomai
code that messes this up on SH4, this has to be fixed. Patching Linux
Linux outside the I-pipe context indicates that something is wrong with
the design. This is what I can say from my distant POV without knowing
the specific issues of SH4.

Jan


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