When using the trap exit, note the following points:
- A skeleton version of DFHTRAP is supplied in both source and load-module
forms. Make sure that the library search sequence in the CICS® startup JCL
finds the correct version of the load module.
- DFHTRAP must save and restore the trace domain’s registers. The supplied
skeleton version contains the code necessary to do this. You are strongly
advised not to change this code.
- The 80-byte work area provided for the sole use of the exit is in working
storage acquired by the trace domain using an MVS™ GETMAIN. It is acquired and initialized
to binary zeros when the trap is activated. It then exists until the trap
is deactivated (CSFE DEBUG,TRAP=OFF). In a CICS transaction dump, the DFHTRAP
working storage can be found soon after the CSA optional features list. The
80-byte work area is at the end of the DFHTRAP working storage and is immediately
preceded by a 16-byte eye-catcher (DFHTRAP_WORKAREA),
so that the work area can be located even if it has not been formatted. In
a CICS system dump, the DFHTRAP working storage is in the trace domain (TR)
section. See Formatting system dumps for details of how to use the TR keyword
to format the trace domain information in the dump.
- DFHTRAP must always run with AMODE(31) and RMODE(ANY) specified. In particular,
it must always return control to the trace domain in 31-bit mode.

Trace domain trace points
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