Parameter Info Block (PIB), all offsets in pointer-length words
   Name          Offset  Meaning
   buffer_size   0       Size of the destination buffer
   
      The total number of bytes in all of the segments that require a
      buffer to be created in the destination address space.  This is
      specified so that the kernel can allocate one large buffer for all
      segments before traversing the segment list.  When returning from a
      method, the buffer size only includes buffers allocated by the
      caller; "inout" segments where the caller specified a non-NULL ptr,
      and the callee did not increase the length, are not included
      (because the kernel does not need to allocate a caller-side buffer
      for them).
                 
   objlist_ptr   1       Pointer to the object list
   objlist_len   2       Length of the object list

      The object list is a list of pointers into segment data describing
      where object IDs can be found.  When copying a segment to the
      destination address space, it will convert all IDs (allocating a new
      ID if necessary).  The object list must be in order (first by
      segment, then by address); an exception may be thrown if it is out
      of order or if it contains invalid entries.  Segments with object
      IDs cannot have the Shared flag.  Unmarshalling code should always
      verify that any ID it expects is actually in the object list.

	ptrlist_ptr   3       Pointer to the pointer list
	ptrlist_len   4       Length of the pointer list
	
	   The pointer list, like the object list, is a list of pointers to
	   segment data.  Each pointer pointed to must also point within
	   segment data, and will be modified by the ORB when copied to point
	   to the equivalent location in the destination address space.  The
	   pointer list must be in order (first by segment, then by address);
	   an exception may be thrown if it is out of order of if it contains
	   invalid entries.  Segments with internal pointers cannot have the
	   Shared flag (shared segments can still be pointed to, of course). 
	   Unmarshalling code should always verify that any internal pointer it
	   expects actually points within a valid segment.

   num_segments  5       Number of data segments
   segment.ptr   6+n*3   Pointer to data segment
   segment.len   7+n*3   Length of data segment in bytes
   segment.flags 8+n*3   Attributes of data segment
   
      Each segment describes data being transmitted to and/or from the
      callee.  For out segments, the caller may designate a buffer to hold
      the data, or it may leave the ptr field NULL.  The caller may
      replace an out segment pointer with its own (it must do this if it
      was NULL), and it may change the length of the segment.  Except when
      flags such as Push or Shared force the kernel to map, rather than
      copy, the data, it will choose which method to use based on the
      size, page-alignment, and overmap status of the segment.

Segment Flags (see doc/orb/memory-management for more details):
   In            0x01    Data is copied/mapped from caller to callee
   Out           0x02    Data is copied/mapped from callee to caller
   Shared        0x04    A permanent shared mapping is created
   Push          0x08    The region is unmapped from the source and
                         transferred to the destination.
   Inline        0x10    The callee cannot change the length of an
                         Out segment.  Ignored for In segments.
   Immutable     0x20    The segment is to be mapped read-only in
                         the destination.
   Copy        0x8000    The segment is permanently copied into the
                         destination address space, with read/write
                         access (unless Immutable is set).