[PATCH 1/3] i386/smp: Define unused CPU_Interrupt_frame to fix compiler error

[Sebastian Huber]

On 12/03/18 13:13, Amaan Cheval wrote:
> Hey! Thanks for the guidance!
>
> I did look at cpu_asm.S, but I don't quite get how Interrupt_frame is being
> used, where by "used" I mean it in the sense that fields within it are
> being set to the actual register values, the way they are with stm/ltm for
> the Context_Control structure.

This structure is used as a temporary stack to allow interrupt 
processing during a context switch. You find some information about this 
here:

https://docs.rtems.org/branches/master/c-user/symmetric_multiprocessing_services.html#thread-dispatch-details

>
> The reason I'm looking for ways in which state values are saved into the
> CPU_Interrupt_frame

The interrupt exception prologue saves the volatile context of the 
interrupted thread into this structure. I guess this is

https://git.rtems.org/rtems/tree/c/src/lib/libbsp/i386/shared/irq/irq_asm.S

I don't know the i386 BSP well and I am not really interested in this 
architecture.

>   struct is because the comment in
> ./cpukit/score/cpu/no_cpu/include/rtems/score/cpu.h says:
>
>       /**
>        * @ingroup Management
>        *
>        * This defines the set of integer and processor state registers that
> must
>        * be saved during an interrupt.  This set does not include any which
> are
>        * in @ref Context_Control.
>        */
>
> In cpu_asm.S, _CPU_Context_switch has only this bit that's relevant to
> Interrupt_frame:
>
>       add sp, r2, #(PER_CPU_INTERRUPT_FRAME_AREA + CPU_INTERRUPT_FRAME_SIZE)
>
> Which is effectively:
>
>       sp = GET_SELF_CPU_CONTROL() + Per_CPU_Control.Interrupt_frame +
> sizeof(CPU_Interrupt_frame)
>
> If the stack grows downwards, I guess pushing to the stack would write to
> the Interrupt_frame?

Yes.

> I'll continue looking at it now that I know this is
> the correct place to look; perhaps what I'm missing is just how the stack
> pointer is used or how interrupts are dispatched?

On ARM, it is in this file:

https://git.rtems.org/rtems/tree/cpukit/score/cpu/arm/arm_exc_interrupt.S

>
>> SMP context switch code (which is incomplete for i386)
> When you say this, does that mean _CPU_Context_switch's bits with "#ifdef
> RTEMS_SMP"

Yes.

>   or do you mean another function altogether?

No, the non-SMP context switch should work fine.

> Sorry if that's a
> stupid question; evidently I'm not familiar enough with RTEMS' internals -
> it's easy to get lost until you find just the right thread to unwind the
> whole thing. :P
>
> P.S. - I'm "amaan" on the #rtems IRC in case you think I've confused myself
> and gone down the wrong path, and it'd be quicker to clarify on chat.
>
> On Mon, Mar 12, 2018 at 12:18 PM Sebastian Huber <
> sebastian.huber at embedded-brains.de> wrote:
>
>> On 10/03/18 15:11, Amaan Cheval wrote:
>>> CPU_INTERRUPT_FRAME_SIZE needs to also be set to allow the
> RTEMS_STATIC_ASSERT
>>> in percpuasm.c to be fulfilled.
>> The CPU_Interrupt_frame must properly defined. It must be used by the
>> SMP context switch code (which is incomplete for i386). Please have a
>> look at the ARM context switch code as an example:
>> https://git.rtems.org/rtems/tree/cpukit/score/cpu/arm/cpu_asm.S
>> --
>> Sebastian Huber, embedded brains GmbH
>> Address : Dornierstr. 4, D-82178 Puchheim, Germany
>> Phone   : +49 89 189 47 41-16
>> Fax     : +49 89 189 47 41-09
>> E-Mail  : sebastian.huber at embedded-brains.de
>> PGP     : Public key available on request.
>> Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.

-- 
Sebastian Huber, embedded brains GmbH

Address : Dornierstr. 4, D-82178 Puchheim, Germany
Phone   : +49 89 189 47 41-16
Fax     : +49 89 189 47 41-09
E-Mail  : sebastian.huber at embedded-brains.de
PGP     : Public key available on request.

Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.