IJ00732: JAVA JIT: INCORRECT RESULTS FOR PATTERNS OF SHIFTED AND OR'D BYTES

APAR status

• Closed as program error.

Error description

• Error Message: Code that accesses successive elements of a byte
  array and combines those elements using a combination of shifts
  and bitwise 'or' operators may produce incorrect results when
  compiled by the JIT.
  Example source code that could be impacted:
  int result = (data[i] & 0xff) | ((data[i+1] & 0xff) << 8) |
  ((data[i + 2] & 0xff) << 16) | (data[i + 3] << 24);
  The problem was introduced in Java 8 SR5 and can only occur when
  running on little endian architectures like Intel, but does not
  effect big endian systems like zOS/zLinux or AIX..
  .
  Stack Trace: N/A
  .
  

Local fix

• The problem can be avoided by setting the following environment
  variable before starting the JVM:
  TR_DisableIORByteSwap=1
  

Problem summary

• A new optimisation was added in 8SR5 that detects patterns of
  successive byte array accesses that are equivalent to a single
  read of a larger entity. Unfortunately the optimisation adapted
  incorrectly to little vs big endian byte in word order.
  

Problem conclusion

• The optimisation has been fixed to return the bytes in the
  expected order.
  .
  This APAR will be fixed in the following Java Releases:
   8 SR5 FP5 (8.0.5.5)
  .
  Contact your IBM Product's Service Team for these Service
  Refreshes and Fix Packs.
  For those running stand-alone, information about the available
  Service Refreshes and Fix Packs can be found at:
   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:

• Fixed component name

  JIT

• Fixed component ID

  620700124

Applicable component levels

• R130 PSY

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