             THEN #SS(0); FI;
    Read return segment selector;
    IF stack segment selector is NULL
         THEN #GP(0); FI;
    IF return stack segment selector index is not within its descriptor table limits
         THEN #GP(selector); FI;
    Read segment descriptor pointed to by return segment selector;
    IF stack segment selector RPL ≠ RPL of the return code segment selector
    or stack segment is not a writable data segment
    or stack segment descriptor DPL ≠ RPL of the return code segmen