VMS Help POSIX Threads, PTHREAD routines, pthread_attr_setstackaddr_np, Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    This routine uses the values specified in the stackaddr and size
    arguments to set the base stack address and size of the thread
    attributes object specified in the attr argument.

    When creating a thread, use a thread attributes object to specify
    nondefault values for thread attributes. The default value for
    the stack address attribute of an initialized thread attributes
    object is NULL.

    Unlike pthread_attr_setstackaddr(), this routine is a much more
    reliable portable interface. With the POSIX standard pthread_
    attr_setstackaddr(), a stack is specified using a single,
    undefined, address. An implementation of the standard can only
    assume that the specified value represents the value to which the
    thread's stack pointer should be set when beginning execution.
    However, this requires the application to know how the machine
    uses the stack. For example, a stack may "grow" either up (to
    higher addresses) or down (to lower addresses), and may be
    decreased (or increased) either before or after storing a new
    value.

    The Threads Library provides an alternative interface with
    pthread_attr_setstackaddr_np(). Instead of specifying a stack
    address, you specify the base (lowest) address and the size.