Adding trace points

Several trace points are predefined into VSAM; each has a unique trace point ID.

If one of these predefined trace points (specifiable by HOOK) is insufficient, you can add your own trace point by providing the code, as follows:

VER nnnn  XXXX,XXXX                             ORIGINAL INSTRUCTION
VER nnn4  ????,???? MAIN                        NEXT SEQUENTIAL INSTRUCTION
VER pppp  ZZZZ,ZZZZ PATCH                       LOCATION OF PATCH
REP nnnn  47F0,pppp       BC    15,PATCH        BRANCH TO THE PATCH
REP pppp  BFFF,3078       ICM   15,15,AMBTRACE  IS TRACE ACTIVE?
REP ppp4  4780,pp10       BZ    EXIT            NO, SKIP HOOK CODE
REP ppp8  58F0,F000       L     15,0(15)        LOAD TRACE ADDRESS
REP pppC  05EF            BALR  14,15           GO TO TRACE
REP pppE  0064            DC    X'0064'         ANY USER'S TRACE POINT ID
REP pp10  XXXX,XXXX EXIT                        ORIGINAL INSTRUCTION
REP pp14  47F0,nnn4       B     MAIN            RETURN TO NEXT SEQUENTIAL
                                                INSTRUCTION

You must ensure that the following registers contain the indicated data:

Failure to have these registers set could cause program checks and other unpredictable results. Register 0 is altered during the execution of trace routine. Care must be used in the selection of trace points, and in the selection of control blocks to be traced, because not all control blocks may be valid at a given time.