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exception_intro(3)
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exception_intro, libexc - an overview of exception support
supplied in libexc.a
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 run-time 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 that they should not cost anything
until they occur. When an exception occurs, the exception
system makes every effort 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 that 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 run-time 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 run-time 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
that determine whether 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 SEE ALSO section for information
on IEEE floating-point exception support.
/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_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
Object File/Symbol Table Format Specification
exception_intro(3)
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