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D.2 Unwinding From Stubs on MPE XL

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Since each stub performs a different function, the unwind routines need to perform stub-specific actions.

Calling Stubs: None of the significant registers are modified; RP still contains the return address.

Called Stubs: All significant registers are on the stack. RP and DP are stored by calling stub, and SID is stored by CALLX. Their locations are: 
    RP  : SP - 24
    SID : SP - 28
    DP  : SP - 32
Parameter Relocation Stubs: It must be determined (from the unwind descriptor) if the current address is before or after the instruction which stores RP on the stack. If it is before the current address, RP still contains the return address; otherwise the return address will be stored on the stack.



D.1 Role of Stubs in Unwinding

D.3 Unwinding From Stubs on HP-UX