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Command: __exc_last_chance | Section: 3 | Source: Digital UNIX | File: __exc_last_chance.3.gz
set_unhandled_exception(3) Library Functions Manual 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
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 virtu-
ally unwinding the stack (see unwind(3)). exc_dispatch_exception in-
vokes 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 per-
form 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 re-
moved 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_unhan-
dled_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_dis-
patcher is installed as the signal handler for SIGSEGV signals, the
dispatcher begins searching for a frame-based handler, by virtually un-
winding 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)). Eventu-
ally 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->Exception-
Code);
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/in-
clude/excpt.h - include file usr/include/pdsc.h - include file usr/in-
clude/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
set_unhandled_exception(3)