For the case where you get control in the same AMODE as the caller (e.g., BALR, BASR, BRASL, etc), and you want to use BAKR/PR to save/restore registers, and your return address is in reg 14, then it is true that
BSM 14,0 BAKR 14,0 is the easiest way to set things up so that PR returns in the AMODE of the caller. There are other, long-winded, ways to accomplish this (that quite possibly no one uses). The principles of operation is not, for the most part, a user's guide. It is a user's manual. Peter Relson z/OS Core Technology Design
