IV64048: INCORRECT RESULT WHEN COPYING ARRAY ELEMENTS BETWEEN OVERLAPPING SOURCE AND DESTINATION SUBRANGES IN A SINGLE JAVA ARRAY ON X86

APAR status

• Closed as program error.

Error description

• Error Message: When this problem is encountered it may manifest
  itself as an exception relating to invalid program data or as
  incorrect program output.
  .
  Stack Trace: N/A
  .
  The problem occurs in rare circumstances where data is being
  copied between overlapping source and destination subranges in a
  single Java array using a loop. The code generated by the JIT
  compiler in these rare circumstances on x86 and POWER systems
  can result in incorrect values being placed in the destination
  range of array elements.
  

Local fix

• The issue can be worked around by using the
  -Xjit:disableIdiomRecognition option. Note that this will likely
  cause a performance degradation.
  

Problem summary

• The problem occurs when a Java application is copying array
  elements between overlapping source and destination subranges of
  a single array using a loop. In some rare circumstances, the JIT
  may generate an optimized implementation of the loop that is not
  functionally equivalent to the original Java loop when executed
  on x86 and POWER systems. This can result in data corruption in
  the array during the copy operation.
  

Problem conclusion

• The JIT has been modified to ensure that code generated is
  always functionally equivalent to the original Java loop and
  will not produce any incorrect values.
  .
  This APAR will be fixed in the following Java Releases:
     6    SR16 FP2  (6.0.16.2)
     6 R1 SR8 FP2   (6.1.8.2)
     7 R1 SR2       (7.1.2.0)
     7    SR8       (7.0.8.0)
  .
  Contact your IBM Product's Service Team for these Service
  Refreshes and Fix Packs.
  For those running stand-alone, Java maintenance is available
  from:
             https://www.ibm.com/developerworks/java/jdk/
  

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:

Fix information

• Fixed component name

  JIT

• Fixed component ID

  620700124

Applicable component levels

• R600 PSY

     UP

• R260 PSY

     UP

• R130 PSY

     UP