Slide 9

Many system calls, such as SETFRR, are privileged calls made by branch entry using a system wide vector table (CVT or SVT) located in shared storage. As a result, these calls cannot be isolated and intercepted at the address space level. TDF provides a special breakpoint called a Branch Entry Intercept (BEI) breakpoint. All branch entry calls start with a load of the vector table address somewhere in PSA followed by a load of the specific vector table entry. Using the provided breakpoint command, a developer could set a breakpoint at the load for the vector table entry. The breakpoint processor will recognize the calling sequence as a system branch entry call and set a special breakpoint. Unlike other breakpoints set by command, branch entry intercept breakpoints persist until they are reset by command or the session ends.

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Currently, only SETFRR is supported. However, SCHEDULE, SCHEDXIT, FESTAE and ESTAE BRANCH=YES are planned for the near future.

The behavior of a branch entry intercept breakpoint is the same as seen for other RTM exit interception.