Program Logic Manual - All about the IBM 1130 Computing System

LOCALs AND SOCALsIf during the first pass the Core Load Builder(phase 4) determines that an Assembler core loadwill not fit into core storage even with any LOCALsthat have been specified, the core load buildingprocess is terminated. However, for a FORTRANcore load special overlays (SOCALs) of parts of thecore load will be created during a second pass ifthis will make the core load fit. The decision ofwhether to proceed with a second pass is made afterphase 4 accounts for the sizes of the LOCAL area,if any, the flipper and its table, and each of theSOCALs. If the check shows that SOCAL option 1(SOCAL 1 and SOCAL 2) will be insufficient, thena further check is made for option 2 (all threeSOCALs). If option 2 is still insufficient, processingis terminated; otherwise, a second pass is made.During pass 2, the entire core load is builtagain, but, unlike during pass 1, subprograms arerelocated in a special order. First, the mainlineand the in-core (class 0) subprograms are relocated,followed by: the flipper; the LOCALs, if any; thearithmetic and function (class 1) subprograms; thenon-disk FIO (class 2) subroutines; and, ifnecessary, the disk FIO (class 3) subroutines.The same procedure described above is necessaryif LOCALs are employed without SOCALs. In otherwords, LOCALs, as well as SOCALs, require twopasses.INTERRUPT LEVEL SUBROUTINES (ILSs)After all other subprograms have been relocated,the Interrupt Transfer Vector (ITV) in the coreimage header is scanned. Except for the entriesfor interrupt levels 2 and 4, a non-zero entrycauses the corresponding ILS to be incorporatedinto the core load. (ILSO2 and ILSO4, unlesssupplied by the user, are a part of the ResidentMonitor.) See Interrupt Branch Table, above,for a description of the processing of that part ofan ILS.TRANSFER VECTOR (TV)The transfer vector consists of two parts: theLIBF TV and the CALL TV, The former providesthe linkage to LIBF subprograms, the latter toCALL subprograms. The LIBF TV was created toenable the LIBF statement to require only onestorage location during execution. This is desirablebecause 1130 FORTRAN object code contains a veryhigh percentage of calls to subprograms. Longbranches to those subprograms would greatly increasecore requirements for core loads over amethod that employs short branches. By replacingthe LIBF statement with a short BSI, tag 3, to atransfer vector entry, which could then supply thelong branch to the desired subprogram, this problemis solved. The cost, of course, is that XR3 is takenaway from the user and the transfer vector is limitedto 255 words, This means the LIBF TV has amaximum of 85 3-word entries, two of which becomethe real-number pseudo-accumulator (FAC) and anindicator for certain arithmetic subroutines. Thus,the user is limited to LIBFs to not more than 83separate subprogram entry points per core load.There is no theoretical limit on the number ofCALL entry points per core load, for the CALLstatement is replaced by an indirect BSI to thedesired subprograms. However, the number ofCALL and LIBF references combined must notexceed the capacity of the Load Table, which isapproximately 150 entries.The CALL TV entry is one word only, the addressof the subprogram entry point. This makes it possibleto replace a CALL statement with an indirectBSI to the corresponding CALL TV entry, even thoughthe address of the subprogram itself may not beknown at the time the CALL is processed.When stored on disk in disk core image format(DCI), the LIBF TV follows the last word of the lastsubprogram in the core load. It may leave one wordvacant between it and the CALL TV in order tomake the pseudo-accumulator (FAC) begin on anodd boundary. The CALL TV immediately followsthe indicator entry in the LIBF TV. During executionthe TV extends downward in core storage fromthe lowest-addressed word in COMMON.Whereas the CALL TV entry consists of only oneword (the address of the subprogram), the LIBF TVentry consists of three words. The first is a linkword (initially zero), and the second and third are along BSC to the subprogram entry point.Figure 10 shows the layout of the transfer vectorin core storage.Linkage to LOCALsThe LOCAL/SOCAL flipper (FLIPR) is included in acore load if that core load requires LOCALs and/orSOCALs. The flipper transfers control to a LOCAL,Section 8. Core Load Builder 37