Call parameter lists

Every callable service is called with a parameter list. As shown in Figure 1, when a service is called:

• Register 1 points to a parameter address list.
• Each field in the parameter address list points to a field containing a parameter.
• The "parameter list" is the set of those parameters; however they are arranged in storage. For AMODE 31 callers, the last parameter pointer in the list must have the high-order bit set to 1. For AMODE 64 callers, there is no end-of-parameter list indicator; the high-order bit is part of the 64-bit address.