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set_unhandled_exception(3)
NAME
  set_unhandled_exception, __exc_last_chance, exc_set_last_chance_handler -
  support routines for unhandled exceptions

SYNOPSIS
  #include <excpt.h>

  void set_unhandled_exception(
	  exception_handler_type handler );

  static void __exc_last_chance(
	  system_exrec_type *exceptionRecord,
	  void *EstablisherFrame,
	  CONTEXT *contextRecord,
	  DISPATCHER_CONTEXT *dispatcherContext );

  void exc_set_last_chance_handler(
	  exception_handler_type last_chance );

LIBRARY
  Exception Handling Library (libexc.a)

PARAMETERS
  handler
      Address of last chance handler.

  exceptionRecord
      Address of primary exception record.

  EstablisherFrame
      Virtual frame pointer of handler's establisher.

  contextRecord
      Pointer to a struct sigcontext (see signal(2)) used to represent a
      procedure's context.

  dispatcherContext
      Address of exception dispatcher's control record.

  last_chance
      Address of last chance handler.

DESCRIPTION
  When called as the result of an exception, exc_dispatch_exception(3)
  attempts to find a handler to process the exception by searching the stack
  frames of procedures in the call chain. It does this by virtually unwinding
  the stack (see unwind(3)). The exc_dispatch_exception() routine invokes a
  handler, if one exists, for each procedure in the call chain until it finds
  one that handles the exception. If no handler handles the exception, the
  dispatcher returns to its caller (for instance, exc_raise_exception(3)).
  The caller typically calls exc_unwind() to perform an exit unwind.

  During an exit unwind, existing handlers for procedures in the call chain
  are invoked with notification that unwinding is in progress, thus allowing
  handlers to perform scope cleanup. Once the stack has been unwound and all
  frames for procedures in the call chain have been removed from the stack,
  __exc_last_chance() is called. It calls a user specified handler, if
  present, or prints a message using stdio and calls exit(2) with an argument
  of 1.

  You can establish a last chance handler by calling either
  set_unhandled_exception() or exc_set_last_chance_handler() specifying a
  nonzero value as a handler. There is only one last chance handler per
  process and it is inherited over forks.

  The type exception_handler_type is defined in excpt.h and matches the
  prototype for __exc_last_chance.

EXAMPLES
  In the following example, exc_set_unhandled_exception() installs
  my_lastchance as the last chance handler. Because the exception_dispatcher
  is installed as the signal handler for SIGSEGV signals, the dispatcher
  begins searching for a frame-based handler, when the segmentation violation
  occurs, by virtually unwinding the context of the current and previous
  procedure call frames. When it determines that no frame-based handler
  exists for this exception, the dispatcher performs an exit unwind of the
  procedure call stack (see exc_resume(3)). Eventually the last-chance
  handler, my_last_chance, executes.

       /*
	* cc -call_shared -o lastchance lastchance.c -lexc
	*/
       #include <stdio.h>
       #include <signal.h>
       #include <excpt.h>

       int     *x = 0;

       EXCEPTION_DISPOSITION
       my_lastchance (
	       system_exrec_type *exceptionRecord,
	       void *establisherFrame,
	       CONTEXT *contextRecord,
	       DISPATCHER_CONTEXT *dispatcherContext)
	   {
	   printf ("Handler: executing...\n");
	   printf ("The signal code is 0x%0lx\n", exceptionRecord->ExceptionCode);
	   printf ("The exception PC is 0x%0lx\n", contextRecord->sc_pc);
	   printf ("Exception Masks: ");
	   /* Print option mask values */
	   if (exceptionRecord->ExceptionFlags & EXCEPTION_NONCONTINUABLE)
	       printf ("NONCONTINUABLE ");
	   if (exceptionRecord->ExceptionFlags & EXCEPTION_UNWINDING)
	       printf ("UNWINDING ");
	   if (exceptionRecord->ExceptionFlags & EXCEPTION_EXIT_UNWIND)
	       printf ("EXIT_UNWIND ");
	   if (exceptionRecord->ExceptionFlags & EXCEPTION_STACK_INVALID)
	       printf ("STACK_INVALID ");
	   if (exceptionRecord->ExceptionFlags & EXCEPTION_NESTED_CALL)
	       printf ("NESTED_CALL ");
	   if (exceptionRecord->ExceptionFlags & EXCEPTION_TARGET_UNWIND)
	       printf ("TARGET_UNWIND ");
	   if (exceptionRecord->ExceptionFlags & EXCEPTION_COLLIDED_UNWIND)
	       printf ("COLLIDED_UNWIND ");
	       printf ("\n");
	   exit (0);
	   }

       /*
	*
	*/

       int
       main ()
	   {
	   struct sigaction action;

	   action.sa_handler = exception_dispatcher;
	   action.sa_mask = 0;
	   action.sa_options = 0;

	   /*
	    * Request frame based exception dispatcher
	    * to be invoked on a signal.
	    */
	   if (sigaction (SIGSEGV, &action, NULL) == -1) {
	       perror ("sigaction");
	       exit (1);
	       }

	   /* establish last-chance handler */
	   set_unhandled_exception (my_lastchance);

	   *x = 55;    /* Let's SEGV now! */

	   return 0;
	   }

FILES
       /usr/ccs/lib/cmplrs/cc/libexc.a -- exception handling library
       /usr/include/excpt.h -- include file
       /usr/include/pdsc.h -- include file
       /usr/include/signal.h -- include file
       /usr/include/machine/fpu.h -- include file

SEE ALSO
  Functions: exception_intro(3), exc_lookup_function_entry(3), signal(2),
  sigaction(2), setjmp(3), exc_unwind(3), exception_dispatcher(3), ieee(3)

  Files: excpt(4), c_excpt(4), signal(4), pdsc(4)

  Assembly Language Programmer's Guide

  Calling Standard for Alpha Systems

Index for Section 3

Alphabetical listing for S

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