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

Amaan Cheval amaan.cheval at gmail.com
Mon Mar 12 12:13:01 UTC 2018

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.

The reason I'm looking for ways in which state values are saved into the
CPU_Interrupt_frame 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
      * be saved during an interrupt.  This set does not include any which
      * in @ref Context_Control.

In cpu_asm.S, _CPU_Context_switch has only this bit that's relevant to


Which is effectively:

     sp = GET_SELF_CPU_CONTROL() + Per_CPU_Control.Interrupt_frame +

If the stack grows downwards, I guess pushing to the stack would write to
the Interrupt_frame? 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?

> 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" or do you mean another function altogether? 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
> > 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

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