For an ESTAE-type recovery routine, if the system cannot obtain storage for an SDWA, the system does not provide one. The case where an SDWA is not provided is rare. Nevertheless, when you design an ESTAE-type recovery routine, you must allow for the possibility of not receiving an SDWA; almost every action an ESTAE-type recovery routine takes must be set up differently to handle the two possibilities.
To check for the presence of the SDWA, the recovery routine checks the contents of GPR 0. If GPR 0 contains 12 (X'0C') the system could not obtain an SDWA. When GPR 0 contains any value other than 12, an SDWA is present, and its address is in GPR 1. When the system provides an SDWA, the system also provides a register save area whose address is in GPR 13.
If an SDWA was not provided GPR 13 does not point to a save area, and your routine must not use the area pointed to by GPR 13.