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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
  contextRecord
	    Pointer to a struct sigcontext (see signal(2)) used to represent
	    a procedure's context.

  returnValue
	    Value to be passed to the continuing code at the completion of
	    the unwind.

  TargetFrame
	    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.

  TargetIP  If TargetRealFrame is nonzero, address within the target
	    invocation at which to continue execution; otherwise this
	    parameter is ignored.

  exceptionRecord
	    Address of primary exception record.

  TargetRealFrame
	    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 exception 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, execution
  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.

Index for Section 3

Alphabetical listing for E

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