exc_resume(3)						     Library Functions Manual						     exc_resume(3)

NAME

       exc_resume,  exc_longjmp,  exc_capture_context,	exc_continue,  exc_unwind, RtlUnwindRfp  - entry points that support resuming execution of
       user code.

LIBRARY

       Exception Handling Library (libexc.a)

SYNOPSIS

       #include <excpt.h> void exc_resume(
		       PCONTEXT 	contextRecord); void exc_longjmp(
		       PCONTEXT 	contextRecord,
		       long		returnValue); unsigned long exc_capture_context(
		       PCONTEXT 	contextRecord); void exc_continue(
		       PCONTEXT 	contextRecord); void exc_unwind(
		       void		 TargetFrame,
		       void		 TargetIp,
		       system_exrec_type *exceptionRecord,
		       long		 returnValue); void RtlUnwindRfp(
		       void		 *TargetRealFrame,
		       void		 *TargetIp,
		       system_exrec_type *exceptionRecord,
		       long		 returnValue);

PARAMETERS

       Pointer to a struct sigcontext (see signal(2)) used to represent a procedure's context.	Value to be passed to the continuing code  at  the
       completion of the unwind.  If nonzero, virtual frame pointer of the target procedure invocation to which the unwind is to be done; if zero,
       specifies that an exit unwind is to be initiated and causes the EXCEPTION_EXIT_UNWIND flag to be set in the exception record.  If TargetRe-
       alFrame	is  nonzero, address within the target invocation at which to continue execution; otherwise this parameter is ignored.	Address of
       primary exception record.  If nonzero, real frame pointer of the target procedure invocation to which the unwind is to be  done;  if  zero,
       specifies that an exit unwind is to be initiated and causes the EXCEPTION_EXIT_UNWIND flag to be set in the exception record.

DESCRIPTION

       exc_resume and exc_continue perform essentially the same operation as longjmp(3). The exc_resume function is a libexc entry point.

       exc_capture_context saves the current procedure context in the struct sigcontext identified by contextRecord.

       exc_longjmp  restores  the  context that was saved by a previous call to exc_capture_context and calls exc_unwind, setting up its arguments
       from information taken from the contextRecord argument. If the returnValue argument is 0 (zero), it is set to 1 (one) before the call.

       exc_unwind initiates an unwind of procedure call frames. It sets the EXCEPTION_UNWINDING flag in  the  exception  flags	of  the  exception
       record,	which  describes  the  machine state at the time of the exc_unwind call. If the TargetFrame argument is zero, then exc_unwind also
       sets the EXCEPTION_EXIT_UNWIND flag.  It then scans the procedure call frames towards the base of the call stack to find the target of  the
       unwind operation.

       RtlUnwindRfp is similar to exc_unwind except that its first argument is a real frame pointer instead of a virtual frame pointer. Real frame
       pointers point to the bottom of the statically allocated portion of a stack frame. Virtual frame pointers point to the  top  of	the  stack
       frame.

       As  it  encounters  each  frame, the unwind code determines the program counter where control left the corresponding function by looking at
       exception handler information in the runtime function table built by the linker. If the respective routine has an exception  handler,  then
       the  unwind  code  calls  it. This handler should perform cleanup code required for that activation.  Programs written in the C programming
       language, which supports structured exception handling, usually contain a try...finally block that implements a	termination  handler  that
       performs  these	chores	(see c_excpt(4)).  The unwind code also calls a handler when it reaches the TargetFrame so that any scope-oriented
       cleanup code or termination handler can execute.  In this case, it sets the EXCEPTION_TARGET_FRAME flag in the ExceptionFlags field of  the
       exception record.

       Once  it finds the TargetFrame (if specified) and calls its handler (if available), exc_unwind: sets the PC to the TargetIp sets the return
       value to be the returnValue argument, if the returnValue argument is non-zero, sets the return value to be the ExceptionCode of the  excep-
       tion record if the returnValue argument is zero calls exc_continue

RETURN VALUES

       The  exc_capture_context  function returns a value of 0 (zero), unless the return is from a call to the exc_longjmp function, in which case
       exc_capture_context returns the non-zerovalue specified in the returnValue argument to exc_longjmp.

       The exc_longjmp function cannot return 0 (zero) to the previous context.  The value 0 is reserved to indicate the actual  return  from  the
       exc_capture_context  function when first called by the program.	If the exc_longjmp function is passed a returnValue parameter of 0, execu-
       tion continues as if the corresponding call to the exc_capture_context function had returned a value of 1.

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),  exception_dispatcher(3),  exc_lookup_function_entry(3),  signal(2),  sigaction(2),  __exc_last_chance(3),
       ieee(3).

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

       Assembly Language Programmer's Guide.

       Calling Standard for Alpha Systems.

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																     exc_resume(3)