Quick method to find the name of the Calling Program:

Infinitely, IBM has kindly provided us with QWVRCSTK at V5.

D GetCaller PR Extpgm('QWVRCSTK')
D 2000
D 10I 0
D 8 CONST
D 56
D 8 CONST
D 15

D Var DS 2000
D BytAvl 10I 0
D BytRtn 10I 0
D Entries 10I 0
D Offset 10I 0
D EntryCount 10I 0
D VarLen S 10I 0 Inz(%size(Var))
D ApiErr S 15

D JobIdInf DS
D JIDQName 26 Inz('*')
D JIDIntID 16
D JIDRes3 2 Inz(*loval)
D JIDThreadInd 10I 0 Inz(1)
D JIDThread 8 Inz(*loval)

D Entry DS 256
D EntryLen 10I 0
D PgmNam 10 Overlay(Entry:25)
D PgmLib 10 Overlay(Entry:35)
D
C CallP GetCaller(Var:VarLen:'CSTK0100':JobIdInf
C :'JIDF0100':ApiErr)
C Do EntryCount
C Eval Entry = %subst(Var:Offset + 1)
C Eval Offset = Offset + EntryLen
C Enddo
C Eval *InLR = *on