Slide 7

TDF uses the standard, documented SVC screen facility of z/OS. It does not replace the SVC calls. Through redirection, it wraps itself around each intercepted SVC call. The preprocess phase determines if a ATTACH, LOAD, LINK or XCTL SVC designates a target program. If not, the call is passed to MVS. If it is a target program, one specified in the TDF intercept command, it creates the trap environment and automatically inserts system breakpoints at the start and end of each function. It does not alter the target program.

TDF also intercepts SPIE, ESPIE, STAE and ESTAE SVC RTM exit calls. Only programs designated as target program are enabled for RTM exit screening. System breakpoints are automatically created each time an RTM exit is set or created, reset or cancelled, called by the RTM, or returns from an RTM call.

Plans are to expand SVC screening to STIMER REAL calls to intercept STIMER exits.

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When debugging multi-tasking scenarios, it’s very important that the programmer have a sound understanding of the inter-relationship between tasks. Otherwise, you can create scenarios where one task is in a wait on another task that is in a diagnostic pause resulting in a seeming deadlock. For these scenarios, TDF provides an ATTN exit that allows you to break out of the wait and connect to the task in the diagnostic pause.