On Alpha and Integrity server systems, adds a specified number of
    demand-zero allocation pages to a process's virtual address space
    for the execution of the current image. Expansion occurs at the
    next free available address within the specified region.

    This service accepts 64-bit addresses.

    Format

      SYS$EXPREG_64  region_id_64 ,length_64 ,acmode ,flags

                     ,return_va_64 ,return_length_64

    C Prototype

      int sys$expreg_64  (struct _generic_64 *region_id_64, unsigned

                         __int64 length_64, unsigned int acmode,

                         unsigned int flags, void *(*(return_va_64)),

                         unsigned __int64 *return_length_64);