IEFBR14

IEFBR14 is an IBM mainframe utility program. It runs in all IBM mainframe environments derived from OS/360, including z/OS. It is a placeholder whose purpose is to do nothing. As it turned out, over the years, it would have problems correctly doing nothing and would sometimes fail in the task.

Purpose

On OS/360 and derived mainframe systems, most programs never directly specify files (usually called datasets) directly, but instead reference them indirectly through the Job Control Language (JCL) statements that invoke the programs. These data definition (or "DD") statements can include a "disposition" (DISP=...) parameter that indicates how the file is to be managed — whether a new file is to be created or an old one re-used; whether the file should be deleted upon completion or retained; etc.

IEFBR14 was created because while DD statements can create or delete files easily, they cannot do so without a program to run. The program used in the JCL does not actually need to use the files to cause their creation or deletion — the DD DISP=... specification does all the work. Thus a very simple do-nothing program was needed to fill that role.

IEFBR14 is used to create or delete a PDS (Partitioned DataSet) or PS (Physical Sequential) from JCL.

Naming

The "IEF" derives from a convention on Mainframe computers that programs supplied by IBM were grouped together by function or creator and that each group shared a three-letter prefix. In OS/360, the first letter was almost always "I", and the programs produced by the scheduler group (including IEFBR14) all used the prefix "IEF". Other common prefixes included "IEB" for dataset utility programs, "IEH" for system utility programs, and "IEW" for program-linkage and -loading.

As explained below, "BR14" was the essential function of the program, to simply return back to the operating system. This portion of a program name was often mnemonic — for example, IEBUPDTE was the dataset utility (IEB) that applied updates (UPDTE) to source code files, and IEHINITT was the system utility (IEH) that initialized (INIT) magnetic tape labels (T).

Usage

Example JCL would be :

//IEFBR14  JOB  ACCT,'DELETE DATASET',MSGCLASS=J,CLASS=A

//STEP0001 EXEC PGM=IEFBR14

//DELDD    DD DSN=xxxxx.yyyyy.zzzzz,

//            DISP=(MOD,DELETE,DELETE),UNIT=DASD

To create a Partioned Data Set:

//TZZZ84R  JOB NOTIFY=&SYSUID,MSGCLASS=X

//STEP01    EXEC PGM=IEFBR14

//DD1       DD DSN=TKOL084.DEMO,DISP=(NEW,CATLG,DELETE),

//             DCB=(RECFM=FB,LRECL=80,BLKSIZE=80,DSORG=PO),

//             SPACE=(TRK,(1,1),RLSE),

//             UNIT=SYSDA

It consisted initially as a single instruction a "Branch to Register" 14. The mnemonic used in the IBM Assembler was BR and hence the name: IEF BR 14.

It didn't set the return code and hence a second instruction had to be added to clear the return code so that it would exit with the correct status.

The machine code for the modified program is:

        SR    R15,R15  put zero into register 15 (return code)

        BR    R14      branch to the address in register 14 (return to scheduler)

History from the RISKS Digest

Here is an article contributed by John Pershing to the RISKS Digest that explains some of the history of IEFBR14:

From: John Pershing 
Date: 25 Jan 88 11:41:42 ESTYou can't even necessarily write the null program without encountering
problems...
There is an apocryphal story about the large number of attempts that were
required in order to produce a "correct" version of MVS's null program,
IEFBR14 (this was done back in the days when MVS was still called OS).
As with all MVS programs, IEFBR14 is called using the standard system
calling conventions, and all it has to do is return successfully.
The first version was something like this:
        IEFBR14 START
                BR    14       Return addr in R14 -- branch at it
                END
First bug: A program indicates its successful completion by zeroing
register 15 before returning; this version of the null program "failed"
every time. Try it again:
        IEFBR14 START
                SR    15,15    Zero out register 15
                BR    14       Return addr in R14 -- branch at it
                END
Much better. However, this caused some-or-other problems with the linkage
editor, since the END statement didn't specify the primary entry point
of the routine. Version three:
        IEFBR14 START
                SR    15,15    Zero out register 15
                BR    14       Return addr in R14 -- branch at it
                END   IEFBR14
At least now, the null program was functionally correct. However, dump
analysis was impeded because the program didn't include its own name in
the source code, as an "eyecatcher" (this is a time-honored convention).
Null program, mark four:
        IEFBR14 START
                USING IEFBR14,15  Establish addressability
                BR    GO          Skip over our name
                DC    AL1(L'ID)   Length of name
        ID      DC    C'IEFBR14'  Name itself
                DS    0H          Force alignment
        GO      SR    15,15       Zero out register 15
                BR    14          Return addr in R14 -- branch at it
                END   IEFBR14
The next change had something esoteric to do with save-area chaining
conventions -- again, for the sake of conventions and to keep the dump
analysis tools happy.
Note that the "null program" has tripled in size: both in terms of the
number of source statements and in terms of the number of instructions
executed!