[PATCH v2 2/6] cpukit: Add Exception Manager

[Sebastian Huber]

On 01/10/2021 21:39, Kinsey Moore wrote:
> 
> Sebastian,
> 
> Could you be more specific about which parts of the 
> architecture-dependent interface still seem tied to the AArch64 port? I 
> thought I had made them sufficiently abstract by relying on 
> architecture-specific functions to manipulate and take action on the 
> exception frame. The signal mapping code written on top of this should 
> work for any architecture that implements those functions and contains 
> no reliance on architecture that I can see. The set of exception classes 
> in particular includes exceptions that don't exist on AArch64, but were 
> added because they're known to be present on SPARC and need to be 
> handled. I'm only really familiar with ARM and AArch64, so that could be 
> why I'm missing it.

I would provide a new CPU feature flag

#define CPU_HAS_EXCEPTION_TO_SIGNAL_MAPPING TRUE|FALSE

If it is TRUE, then the CPU port shall provide:

/**
  * @retval -1 There is no signal associated with the exception.
  * @retval SIGSEGV, SIGFPE, ...
  */
int _CPU_Exception_frame_get_signal( const CPU_Exception_frame *frame );

RTEMS_NO_RETURN _CPU_Exception_resume( CPU_Exception_frame *frame );

The architecture-independent part just needs to provide a fatal extension:

_Thread_local Thread_Action _Exception_Raise_signal_action;

void _Exception_Raise_signal( source, true, code )
{
   int sig;

   if ( source != RTEMS_FATAL_SOURCE_EXCEPTION ) {
     return;
   }

   sig = _CPU_Exception_frame_get_signal( code );

   switch ( sig ) {
     case SIGSEGV:
       handler = _Exception_Raise_sigsegv;
       break;
     default:
       return;
   }

   _Thread_Prepend_post_switch_action( executing, 
&_Exception_Raise_signal_action, handler );

   _CPU_Exception_resume( code );
}

Using a post-switch extension has the benefit that you don't have to 
call the complicated raise() function in the exception context. It is 
called in thread context.

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