Execution control

You can single-step through a program. If a Disassembly window is open as the program progresses, the next instruction to be executed is highlighted.

You can use exit routines, written in REXX or compiled languages, to examine conditions surrounding a breakpoint and determine whether or not to inform you of its occurrence, or to ignore the breakpoint and continue execution.

By using the PATH option you can capture the number of times each instruction in your program is executed. This can be helpful in locating "dead code".

You can use the HISTORY command to review the last 1,023 machine instructions executed by your program. This is often useful in determining the circumstances leading to a "wild branch" or similar error.

An exit routine can use the MSTEP command to perform a dynamic path analysis of your program. (This analysis is slow, since part of a REXX exit routine is executed for each instruction your program executes.)

z/VM®

If Extended Control (EC) mode is available to IDF, PER is used to provide register or storage alteration stops. Breakpoints and single-step mode are available regardless of EC mode availability.

All SVC instructions issued by your program can be trapped.

If your program invokes a nucleus extension through BALR linkage, an option lets you single-step through that nucleus extension.

IDF can debug programs that "steal" the new PSWs, if your program's instructions which access these PSWs are declared to IDF.