[PATCH] score/i386: Add context switch restore external symbol as a marker.

[Chris Johns]

On 22/07/2016 16:44, Sebastian Huber wrote:
>>>>
>>>> The stack pointer is part of the context. If you retrieve the PC from
>>>> here it should work for all threads.
>>>
>>> All threads on the i386 arch or all threads on all archs?
>>>
>>> I would like to make this simpler for all archs. I do not mind if we
>>> require something being added to each arch to do this but I would
>>> like an interface somewhere and somehow.
>>
>> I don't think that the thread context reconstruction can be done in an
>> architecture independent way. You have different register sets and
>> different ways to store the PC. For example on x86 the PC is on the
>> stack, on ARM you have Context_Control::register_lr, on PowerPC
>> ppc_context::lr which is embedded in Context_Control due to cache line
>> alignment, on SPARC you have Context_Control::o7, and so on.

Sorry, I was meaning just a way to get the PC.

>> I would rather provide a global function that provides the data for
>> your consumer (libunwind?) with a common interface for all
>> architectures and an architecture dependent implementation. The
>> debugger could call this function.

The consumer is a thread aware TCP gdb server running in RTEMS.

>
> For the stack checker extension we have for example _CPU_Context_Get_SP().
>

_CPU_Context_Get_PC() ?

I would like this to be localised to the CPU implementation and 
something that is figured out when a new port is done.

Chris