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

    This routine obtains the value of the stack address attribute of
    the thread attributes object specified in the attr argument and
    stores it in the location specified by the stackaddr argument.
    The specified attributes object must already be initialized when
    this routine is called.

    The stack address attribute of a thread attributes object points
    to the origin of the stack for a new thread.

    Unlike pthread_attr_getstackaddr(), this routine is a much more
    reliable portable interface. With the POSIX standard pthread_
    attr_getstackaddr(), 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_getstackaddr_np(). Instead of returning a stack
    address, it returns the base (lowest) address and the size.