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set_unhandled_exception(3)
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set_unhandled_exception, __exc_last_chance,
exc_set_last_chance_handler - support routines for unhandled
exceptions
#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 );
Exception Handling Library (libexc.a)
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.
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.
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;
}
/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
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
set_unhandled_exception(3)
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