Finding the z/OS Sysname in CICS

Looking in SYS1.MACLIB(CVT), we see that z/OS has a control block called the CVT (Communications Vector Table) that contains the sysname 340 bytes into it. In the comments at the top of that member, we learn that there is a pointer to the CVT in the PSA (Prefixed Save Area) x’10′ bytes into it. The PSA is easy to find – it is at address 0. So, armed with this info, I wrote the sample code below, which you are welcome to use or incorporate into your own project. If you use this code, just define a PPT for it (if you do not use autoinstall for programs) and point a tranid to the program.

IDENTIFICATION DIVISION.
PROGRAM-ID. CVTTEST.

ENVIRONMENT DIVISION.
DATA DIVISION.
WORKING-STORAGE SECTION.

01 WS-PSA-POINTER.
10 PSA-PTR-PIC9 PIC S9(8) COMP-5 VALUE 0.
10 PSA-PTR REDEFINES PSA-PTR-PIC9 POINTER.

01 SEND-AREA.
10 FILLER PIC X(1) VALUE SPACE.
10 FILLER PIC X(11) VALUE 'CVTSNAME = '.
10 SA-CVTSNAME PIC X(8) VALUE SPACES.

LINKAGE SECTION.

01 PSA.
10 FILLER PIC X(16).
10 CVT-PTR POINTER.

01 CVT.
10 FILLER PIC X(340).
10 CVTSNAME PIC X(8).

EJECT

PROCEDURE DIVISION.

100-MAINLINE.

SET ADDRESS OF PSA TO PSA-PTR.
SET ADDRESS OF CVT TO CVT-PTR.

MOVE CVTSNAME TO SA-CVTSNAME.

EXEC CICS SEND FROM(SEND-AREA)
LENGTH(LENGTH OF SEND-AREA)
END-EXEC.

999-RETURN.

EXEC CICS RETURN
END-EXEC.

GOBACK.