SMP Problem on i386

[Sebastian Huber]

Hello,

I found the problem.  The startup code for secondary processor uses this 
(smp-imps.c):

static int
boot_cpu(imps_processor *proc)
{
   [...]
   reset[1] = (uint32_t)secondary_cpu_initialize;
   reset[2] = (uint32_t)_Per_CPU_Get_by_index(apicid)->interrupt_stack_high;
   [...]

Thus the startup code uses the interrupt stack of the processor.

In _CPU_Context_switch we have:

SYM (_CPU_Context_switch):
         movl      RUNCONTEXT_ARG(esp),eax  /* eax = running threads context */
         pushf                              /* push eflags */
         popl      REG_EFLAGS(eax)          /* save eflags */
         movl      esp,REG_ESP(eax)         /* save stack pointer */
         movl      ebp,REG_EBP(eax)         /* save base pointer */
         movl      ebx,REG_EBX(eax)         /* save ebx */
         movl      esi,REG_ESI(eax)         /* save source register */
         movl      edi,REG_EDI(eax)         /* save destination register */

         movl      HEIRCONTEXT_ARG(esp),eax /* eax = heir threads context */

restore:
         pushl     REG_EFLAGS(eax)          /* push eflags */
         popf                               /* restore eflags */
         movl      REG_ESP(eax),esp         /* restore stack pointer */
         movl      REG_EBP(eax),ebp         /* restore base pointer */
         movl      REG_EBX(eax),ebx         /* restore ebx */
         movl      REG_ESI(eax),esi         /* restore source register */
         movl      REG_EDI(eax),edi         /* restore destination register */
         ret

The eflags are restored before the stack pointer restore.  Thus in case an 
interrupt is pending this interrupt will store the thread context on the stack 
which it will use later destroying this context!

On 2013-07-30 17:51, Sebastian Huber wrote:
> Hello,
>
> if I apply the following patch
>
> diff --git a/cpukit/score/include/rtems/bspsmp.h
> b/cpukit/score/include/rtems/bspsmp.h
> index ec8be9f..69cbff4 100644
> --- a/cpukit/score/include/rtems/bspsmp.h
> +++ b/cpukit/score/include/rtems/bspsmp.h
> @@ -104,8 +104,7 @@ void bsp_smp_broadcast_interrupt(void);
>    * This function must not be called by the main processor.  This function does
>    * not return to the caller.
>    */
> -void rtems_smp_secondary_cpu_initialize( void )
> -  RTEMS_COMPILER_NO_RETURN_ATTRIBUTE;
> +void rtems_smp_secondary_cpu_initialize( void );
>
>   /**
>    *  @brief Process the incoming interprocessor request.
>
> then the i386 SMP test cases fail on Qemu.  I get a General Protection Fault
> after the "iret" in _ISR_Handler.
>
> What could be the reason for this?
>


-- 
Sebastian Huber, embedded brains GmbH

Address : Dornierstr. 4, D-82178 Puchheim, Germany
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