Index for Section 3

Alphabetical listing for E

Bottom of page

exception_intro(3)
NAME
  exception_intro, libexc  - an overview of exception support supplied in
  libexc.a.

DESCRIPTION
  The exception mechanism used on Tru64 UNIX requires no execution time in
  user code. The only costs before an exception occurs are one-time
  registering and deregistering of modules with the runtime exception
  handling mechanism from the init and fini sections. This one-time cost is a
  requirement to support shared objects.

  After an exception, there are costs to find exception handling and unwind
  information for procedure activations on the stack.  This model assumes
  that exceptions are exceptional occurrences and they should not cost
  anything until they occur. The exception system makes every effort when an
  exception occurs to be as efficient as possible by using mechanisms such as
  binary searches and software caches where applicable.

  The routines in this section come from four sources, although these
  routines might not have the same names as the routines in the sources:

    ·  ULTRIX libexc.a

    ·  NT defined interfaces

    ·  Calling Standard for Alpha Systems

    ·  new routines required for this implementation

  There may be multiple routines which do the same things but are supported
  for backward compatibility. The data structures are defined in excpt(4),
  pdsc(4) and the Calling Standard for Alpha Systems .

  If you have used the runtime procedure descriptor from ULTRIX libexc as an
  opaque pointer, your code will port easily. If not, you must modify field
  names to match the new data structures.

  The exception system supports three basic services:

    ·  unwinding

    ·  access to procedure specific information

    ·  exception management

  Unwinding support includes the ability to get a context, virtual and actual
  unwinding of levels of procedure activations from the stack and continuing
  execution in a handler or other user code. Some of the unwind routines also
  support invoking handlers as they unwind so that the language or user can
  clean up items at particular procedure activations.


  The routines that provide access to procedure specific information can map
  an address anywhere in a routine to the routine's information.  This
  information includes enough data to cause an unwind or determine if a
  routine handles an exception.	 Typically these routines take an address and
  then binary search a compiler system-created table for an entry covering
  the address.	These routines also contain support for multiple tables so
  that shared objects and runtime generated code can participate in the
  exception system.

  The exception management routines provide ways for languages or users to
  raise exceptions or cause signals to raise exceptions.  The exception
  management routines also provide the mechanism to dispatch the exceptions
  to the appropriate handlers. Typically, languages provide handlers which
  determine if the user has specified a handler for a particular address and
  exception. In the case of structured exception handling in C, the language
  specific handler invokes a routine containing user supplied code to
  determine what action to take (see c_excpt(4) for information on C-style
  structured exception handling). Language specific handlers can either
  handle the exception or return for some other procedure activation to
  handle it.

  The following routines are described in Section 3 reference pages:

  ______________________________________________________________
  Routine			      Description
  ______________________________________________________________

  exc_continue

				      Like longjmp(3)

  exc_dispatch_exception

				      Deliver exceptions to
				      language handlers

  exc_longjmp

				      Like longjmp(3) except
				      calls handlers for cleanup

  exc_lookup_function_entry

				      Map address to procedure
				      information

  exc_lookup_function_table_address

				      Map address to table
				      containing procedure
				      information

  exc_lookup_gp

				      Map address to GP value
				      for a procedure

  exc_raise_exception

				      Raise exception given
				      exception structure

  exc_raise_status_exception

				      Raise exception given
				      exception code

  exc_set_last_chance_handler

				      Set user handler for
				      unhandled exceptions

  exc_unwind

				      Actual unwind invoking
				      cleanup handlers

  __exc_last_chance

				      Unhandled exception
				      handler

  exc_resume

				      Like longjmp(3)

  exception_dispatcher

				      Take signal(2) arguments
				      and raises exceptions


  exc_find_frame_ptr

				      Returns static link of
				      current activation

  find_rpd

				      Maps address to procedure
				      information

  exc_add_gp_range

				      Register range of address
				      for a GP value

  exc_add_pc_range_table

				      Register procedure
				      information table

  exc_remove_gp_range

				      Deregister range of
				      addresses for a GP value

  exc_remove_pc_range_table

				      Deregister procedure
				      information table

  exc_raise_signal_exception

				      Take signal(2) arguments
				      and raises exceptions

  set_unhandled_exception

				      Set user handler for
				      unhandled exceptions

  unwind

				      Virtual unwind updating
				      activation context

  exc_virtual_unwind

				      Virtual unwind updating
				      activation context
  ______________________________________________________________

  See the IEEE routines in the RELATED INFORMATION section for information on
  IEEE floating point exception support.

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_dispatcher(3), exc_lookup_function_entry(3),
  signal(2), sigaction(2), setjmp(3), exc_unwind(3), __exc_last_chance(3),
  ieee(3).

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

  Programmer's Guide.

  Assembly Language Programmer's Guide.

  Calling Standard for Alpha Systems.

Index for Section 3

Alphabetical listing for E

Top of page