Re: [Xenomai-core] [PowerPC] Registers Corruption at Context Switch

[Philippe Gerum <rpm@xenomai.org>]

Benjamin ZORES wrote:
> Hi,
> 
> I'm facing a problem with the PowerPC version of Xenomai/Adeos that I 
> have difficulties
> to identify the exact source.
> 
> I'm running a Xenomai RT kernel thread that use to crash sometimes due 
> to potential register corruption.
> Problem occurs after a context switch and, in some cases, if the task 
> gets interrupted and reschedule,
> its registers values are not the same as they used to be before context 
> switch.
> 
> The code is a bit complex and so, makes use of register that is 
> generally rarely used (GPR r26 to be accurate).
> Driver is compiled with -02 and compiling with -O0 (so disabling 
> optimizations and so, not using r26) works fine
> but is not what I'm looking for.
> 
> Can someone tell me where exactly in Adeos/Xenomai is context switching 
> actually performed and where are the registers save/restore functions ? 
> I've seen there is specific code for FPU registers handling but can't 
> find the equivalent for GPR.
> 
> FYI, I'm running on PowerPC 603e core with Linux 2.6.23, Adeos 2.0-09 
> (latest) and Xenomai 2.3.4 (latest).
> I've seen there are adeos updates (but for updated kernels) but is there 
> some ChangeLog of Adeos changes ?
> Maybe this is a known bug that has been fixed in updated Adeos release ?
> 
> Thx to anyone who can help me on this,
> 

See arch/powerpc/switch_32.S, rthal_switch_threads(), for the part that does the
actual stack switching.

Note that this code is obfuscated by the fact that we have to handle so-called
"hybrid" switching, between Xenomai kernel threads (which do not rely on a
task_struct), and Linux tasks (Xenomai userland, Linux kthreads, or regular
userland Linux). Fortunately, what is saved on the stack in any case is easy to
find out.


> Ben
> 
> 
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-- 
Philippe.