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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

LIBRARY
  Exception Handling Library (libexc.a)

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);

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)).	exc_dispatch_exception 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, such
  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. __exc_last_chance calls a user specified
  handler, if present, or print a message using stdio and call 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 non-
  zero 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, by virtually unwinding the
  context of the current and previous procedure call frames, when the
  segmentation violation occurs. 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...0);
	   printf ("The signal code is 0x%0lx0, exceptionRecord->ExceptionCode);
	   printf ("The exception PC is 0x%0lx0, contextRecord->sc_pc);
	   printf ("Exception Masks: ");
	   /* Print flag 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 ("0);
	   exit (0);
	   }

       /*
	* main program
	*/

       int
       main ()
	   {
	   struct sigaction action;


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

RELATED INFORMATION
  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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