SVC routines are entered with the following data in the general
purpose registers:
- Registers 0, 1, 13, and 15 – Contents when the SVC instruction
was processed.
- Register 3 – Address of the CVT.
- Register 4 – Address of the TCB.
- Register 5 – Address of the current RB (for type 1 or type
6 SVC), or address of the SVRB for SVC routine (for type 2, 3, or
4 SVC).
- Register 6 – Address of the SVC routine entry point.
- Register 7 – Address of the ASCB.
- Register 14 – Return address.
- Other registers – Unpredictable.