Linking a Program

Figure 3-3 Linking and Using User Libraries

• Search one or more relocatable libraries (RLs) and resolve references to them in any of the relocatable object modules being linked.

• Resolve references among the relocatable object modules.

• Merge all the relocatable object modules associated with one program to create an executable program file.

Creating Executable Program Files

The MPE/iX command :LINK creates a load module (an executable program file). The :LINK command invokes Link Editor, which is an MPE/iX subsystem that prepares compiled programs for execution and maintains libraries. When invoked by using :LINK, Link Editor resolves external references in relocatable object modules by merging relocatable object modules to produce an executable program file containing all of the code and data that was in the relocatable object modules.

It assigns final addresses to each symbol (for a variable or procedure) to ensure that none overlap each other in the executable program file. These addresses are called virtual addresses, because they are still subject to a final relocation when the program is loaded into physical memory. Once virtual addresses are determined, Link Editor can resolve many of the references that could not be resolved at compile time, because the symbol tables from all of the relocatable object modules have been merged to one table. You can specify the relocatable libraries to search for unresolved references at link time. Any remaining external calls must be resolved at load time.

:LINK parameters can specify indirect files. An indirect file is a file list contained in an ASCII file. For example, in the :LINK command, an indirect file can be used to specify one of the following lists:

For an overview of Link Editor, refer to Chapter 4. For detailed information on :LINK and Link Editor, refer to Link Editor/XL Reference Manual (32650-90030).

You can request options at link time to:

Symbol Listing

Example 3-1 shows a source file named EX1SRC. An executable program file has been created for EX1SRC named EX1PROG.

   IDENTIFICATION DIVISION.
   PROGRAM-ID. EX1
   ENVIRONMENT DIVISION.
   INPUT-OUTPUT DIVISION.
   FILE-CONTROL.
        SELECT IFILE             ASSIGN "IFILE".
        SELECT PFILE             ASSIGN "PFILE".
   DATA DIVISION.
   FILE SECTION.
   FD   IFILE.
   01   IREC.
        05  NAME                 PIC X(30).
        05  SOC-SEC              PIC X(9).
        05  HIRE-DATE.
            10 MO                PIC XX.
            10 DA                PIC XX.
            10 YR                PIC XX.
        05  SALARY               PIC S9(6).
        05                       PIC X(29).
   FD  PFILE.
   01  PREC.
        05  SOC-SEC              PIC X(9).
        05                       PIC XX.
        05  NAME                 PIC X(30).
        05                       PIC XX.
        05  HIRE-DATE.
            10 MO                PIC XX.
            10                   PIC X.
            10 DA                PIC XX.
            10                   PIC X.
            10 YR                PIC XX.
        05                       PIC X(81).
   01   HREC.
        05  HSOC-SEC             PIC X(11).
        05  HNAME                PIC X(32).
        05  HHIRE-DATE           PIC X(89).
   WORKING STORAGE SECTION.
   01  LNCNT                     PIC S9(4) BINARY VALUE 60.
   01  W-DATE.
        05  WYR                  PIC XX.
        05                       PIC X(4).
   PROCEDURE DIVISION.
   P1.
        ACCEPT W-DATE FROM DATE.
        OPEN INPUT IFILE OUTPUT PFILE.
        PERFORM WITH TEST AFTER UNTIL SOC-SEC OF IREC = ALL "9"
             READ IFILE
                  AT END MOVE ALL "9" TO SOC-SEC OF IREC
                  NOT AT END
                       IF WYR = YR OF IREC THEN
                            ADD 1 TO LNCNT
                            IF LNCNT > 50 PERFORM HEADINGS END-IF
                            MOVE SPACES TO PREC
                            MOVE CORR IREC TO PREC
                            WRITE PREC AFTER ADVANCING 1 LINE
                       END-IF
                  END-READ
             END PERFORM
        CLOSE IFILE PFILE
        STOP RUN.
   HEADINGS.
        MOVE "SOC-SEC" TO HSOC-SEC.
        MOVE "NAME" TO HNAME.
        MOVE "HIRE DATE" TO HHIRE-DATE.
        WRITE PREC AFTER ADVANCING PAGE.
        MOVE 0 TO LNCNT.

The commands

   :LINKEDIT

   LinkEd> LISTPROG EX1PROG

invoke HP Link Editor/XL and create a program map displaying the symbols in EX1PROG, as shown in the following example:

   PROGRAM        : EX1PROG
   XL LIST
   CAPABILITIES   :  BA, IA
   HEAP SIZE      :
   STACK SIZE     :
   VERSION        : 85082112

   Sym             C H X P Sym    Sym         Sym       Lset
   Name                    Type  Scope       Value      Name
   ----            - - - - ----  -----       -----      ----
   $START          0   3 3 sec_p univ        000059B7
   _start          0   3 3 sec_p univ        00005A07
   ex1             0   3 3 pri_p univ        000059EB
   M$1             0       data  local    dp+00000000

In this program map, the portion preceding the symbol table is the header, which provides general information about the executable program file:

The header information is followed by a list of symbols in the executable program file. For information on understanding the symbol listing, refer to Link Editor/XL Reference Manual (32650-90030).