Issuing MVS macros in AR mode

Many MVS™ macro services support callers in both primary and AR modes. When the caller is in AR mode, the macro service must generate larger parameter lists at assembly time. The increased size of the list reflects the addition of ALET-qualified addresses. At assembly time, a macro service that needs to know whether a caller is in AR mode checks the global bit that SYSSTATE ASCENV=AR sets. Therefore, it is good programming practice to issue SYSSTATE ASCENV=AR when a program changes to AR mode and issues macros while in that mode. Then, when the program returns to primary mode, issue SYSSTATE ASCENV=P to reset the global bit.

When your program is in AR mode, keep in mind these two facts:

Before you use a macro in AR mode, check the description of the macro in z/OS MVS Programming: Assembler Services Reference ABE-HSP or z/OS MVS Programming: Assembler Services Reference IAR-XCT. If the description of the macro does not specifically state that the macro supports callers in AR mode, use the SAC instruction to change the ASC mode and use the macro in primary mode.
ARs 14 through 1 are volatile across all macro calls, whether the caller is in AR mode or primary mode. Don't count on the contents of these ARs being the same after the call as they were before.