HLASM - BASR = Branch And Save Register

The opcode of the BASR instruction is X'0D'.

Usage

  1. Branch to a subroutine in a different CSECT - provided that it can be invoked in the same addressing mode as the caller. In this case R14 and R15 are usually used for the return address and destination address respectively.
  2. Branch to a subroutine in the same CSECT - provided that it can be invoked in the same addressing mode as the caller, which will normally be the case. It is not unusual to use other (less volatile) registers than R14 and R15 in this case.
  3. Obtain addressability to the current routine.

Arguments

  1. Register to receive the return address.
  2. Register holding the destination address.

Function

  1. The processor places the address of the byte following the BASR instruction (which is both the next sequential instruction address and the expected return address) in the first register.
  2. It branches to the address specified in the second register.
  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.
  2. If the second argument is register 0, then no branch will be taken; only the return information is placed in the first register.

Related Instructions

  1. BAS branches to a routine that is directly addressable in base-displacement form.
  2. BCR is the preferred return instruction.
  3. BASSM branches to another routine that may need to be called in a different Amode.

Hardware

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

Remarks

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

Examples

         YREGS                          * Define register names
ENTRY    BASR  R15,R0                   * Obtain routine address
USEBASE  USING USEBASE,R15              * Make code addressable
         ...
         LA    R15,=V(SUBPROG)          * Load address of subroutine
         BASR  R14,R15                  * Call subprogram
         ...

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