Content-type: text/html Man page of set_unhandled_exception

set_unhandled_exception

Section: C Library Functions (3)
Index Return to Main Contents

 

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

Address of last chance handler. Address of primary exception record. Virtual frame pointer of handler's establisher. Pointer to a struct sigcontext (see signal(2)) used to represent a procedure's context. Address of exception dispatcher's control record. 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...);
    printf ("The signal code is 0x%0lx, exceptionRecord->ExceptionCode);
    printf ("The exception PC is 0x%0lx, 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 (");
    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.

delim off


 

Index

NAME
LIBRARY
SYNOPSIS
PARAMETERS
DESCRIPTION
EXAMPLES
FILES
RELATED INFORMATION

This document was created by man2html, using the manual pages.
Time: 02:40:49 GMT, October 02, 2010