On Alpha and Integrity server systems, allows a process to change
    the size of its supervisor, executive, and kernel stacks by
    altering the values in the stack limit for a memory stack or a
    register stack and base arrays held in P1 (per-process) space.

    Format

      SYS$SETSTK_64  start_va_64 ,length_64 ,acmode, flags,

                     prev_start_va, prev_length

    C Prototype

      int sys$setstk_64  (void *start_va_64, unsigned __int64

                         length_64, unsigned int acmode, unsigned int

                         flags, void ** prev_start_va_64, unsigned

                         __int64 * prev_length_64);