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

    This routine uses the value specified in the stackaddr argument
    to set the stack address attribute 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 stack address
    attribute of a thread attributes object points to the origin
    of the stack for a new thread.

    The default value for the stack address attribute of an
    initialized thread attributes object is NULL.

                                   NOTE

       Correct use of this routine depends upon details of the
       target platform's stack architecture. Thus, this routine
       cannot be used in a portable manner.

       The size of the stack must be at least PTHREAD_STACK_MIN
       bytes (see the pthread.h header file). However, because the
       Threads Library must use a portion of this stack memory to
       begin thread execution and to maintain thread state, your
       program's "user thread code" cannot rely on using all of the
       stack memory allocated.

    For your program to calculate a value for the stackaddr
    attribute, note that:

    o  Your program must allocate the memory that will be used for
       the new thread's stack.

    o  On Tru64 UNIX, to create a new thread using a thread
       attributes object, the stackaddr attribute must be an address
       that points to the high-memory end of the memory region
       allocated for the stack. This address must point to the
       highest even-boundary quadword in the allocated memory region.

    Also note that:

    o  If you use the pthread_attr_setstackaddr() routine to set a
       thread attributes object's stack address attribute and use
       that attributes object to create a new thread, the Threads
       Library ignores the attributes object's guardsize attribute
       and provides no thread stack guard area or overflow warning
       area for the new thread.

    o  If you use the same thread attributes object to create more
       than one thread and each created thread uses a nondefault
       stack address, you must use the pthread_attr_setstackaddr()
       routine to set a unique stack address attribute value for each
       new thread created using that attributes object.