CNOP

CNOP instructs the assembler to advance the location counter to a designated halfword displacement from a fullword, doubleword, or quadword boundary, by inserting null BCR and BC instructions to fill halfwords and fullwords.

BEGIN    EQU   *                        LOC CTR = 152 = 9(16) + 8 
         CNOP  2,16                     ALIGN TO 1ST HW AFTER QW BOUND
         BCR   0,0                      ADVANCE 2
         BC    0,X'700'                 ADVANCE 4
         BC    0,X'700'                 ADVANCE 4
END      EQU   *                        LOC CTR = 162 = 10(16) + 2

Use CNOP to prevent slack bytes between an instruction that loads a linking register and the aligned data following it.

         CNOP  0,4                      ALIGN BAS TO SAVEAREA
         BAS   R12,CONT                 LEN = 4
SAVEAREA DC    18F'0'                   FW ALIGNED
CONT     DS    0H

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