HLASM - BAS = Branch And Save

The opcode of the BAS instruction is X'4D'.


  1. Branch to a subroutine in the current CSECT


  1. Register to receive the return address.
  2. destination address (index, base, displacement).


  1. The processor places the address of the byte following the BAS instruction (which is both the next sequential instruction address and the expected return address) in the first register.
  2. It branches to the destination address.
  3. The condition code does not change.

Special Cases

  1. Only if the processor is in Amode 31, then the high-order bit of the 32-bit return address will be set to 1.

Related Instructions

  1. BASR branches to a routine whose address is contained in a register.
  2. BCR is the preferred return instruction.
  3. BASSM branches to another routine that may need to be called in a different Amode.


  1. The BAS instruction was introduced with the 370/XA architecture.


  1. The PSW's Amode setting determines how many bits are used for the return and destination addresses.


         YREGS                          * Define register names
ENTRY    BASR  R15,R0                   * Obtain routine address
USEBASE  USING USEBASE,R15              * Make code addressable
         BAS   R14,SUBRTN               * Call subprogram
SUBRTN   DS    0H                       * Align routine to halfword
         ...                            * Subroutine logic goes here
         BR    R14                      * Return to caller

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