PI72387: ABEND 0C4 MAY OCCUR WHEN READING FROM CONCATENATED DD USING QSAM

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• An abend s0C4 may occur when using fread() to read from a DD
  statement with concatenated statements if unable to open one of
  the subsequent definitions and the DD is opened using the QSAM
  access method ("noseek" specified on fopen()).
  
  For example, an input DD defined as:
  //INPUT    DD *
  Testdata
  //         DD DSN=MEGA.JCL(NOMEM),DISP=SHR
  
  and opened with:  fopen("DD:INPUT","rb,noseek");
  [the 'noseek' keyword will drive QSAM]
  
  After reading the valid data, and switching to the invalid
  dataset in the concatenation, a DFSMS failure may surface, but
  the LE C Run-Time ignores the abend and returns to the caller.
  Then on a subsequent fread(), an abend s0C4 may occur when
  trying to branch to the QSAM GET macro - but the DCB may no
  longer be valid.
  
  An example traceback of the 0C4:
  CEL4IO31    -05FE29D8    CEEEV003            Exception
  rp39        +00000110    CEEEV003   HLE77A0  Call
  fread       +0000052C    CEEEV003   HLE77A0  Call
  main        +000000E2    FREADDD             Call
  EDCZMINV    +000000C0    CEEEV003            Call
  CEEBBEXT    +000001C6    CEEPLPKA   HLE77A0  Call
  
  
  Verification Steps:
  1) Verify dataset is concatenated in the JCL, and being opened
     for reading using the 'noseek' keyword on fopen()
  
  2) Verify fopen() is successful.
  
  3) Observe if a DFSMS condition occurs, such as a s013 or s913
     abend, and program control returns to the application.
  
  4) From a dump, determine if an 0C4 condition is encountered
     because the DCB+x31 value which should point to the GET
     macro is no longer valid.
  

Local fix

• Correct the invalid/inaccessible statement in the JCL
  

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * Any z/OS C/C++ application using fread()                     *
  * on a concatenated DDname opened as binary                    *
  * I/O (rb) with the noseek option or a OS                      *
  * file opened using record I/O (type=record)                   *
  * and the noseek option.                                       *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * When reading from a concatenated DDname                      *
  * a S0C4 abend may occur when one of                           *
  * the concatenated datasets is either                          *
  * non-existent or one the application                          *
  * does not have access to.                                     *
  * The abend issued by DFSMS when it                            *
  * switches datasets is improperly ignored                      *
  * by the C run time library.                                   *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  See problem description.
  

Problem conclusion

• The code was changed to add a check for the ABEND
  and to mark the file as unusable.
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

  UI46660 UI46661 UI47644

Modules/Macros

• EDC40045 CELHP083 CELHP039 CELQP083 CELQP039 EDC40051 EDCERNO2
  

Fix information

• Fixed component name

  LE C LIBRARY

• Fixed component ID

  568819805

Applicable component levels

• R7A0 PSY UI46660

     UP17/06/02 P F705

• R790 PSY UI46661

     UP17/06/02 P F705

• R7B0 PSY UI47644

     UP17/06/17 P F706

Fix is available

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