IJ10920: INCORRECT RESULT OR CRASH FROM J9VMINTERNALS.FASTIDENTITYHASHCODE RUNNING JAVA 8 PRIOR TO SR5FP11

APAR status

• Closed as program error.

Error description

• Error Message: The problem can manifest as a crash running
  J9VMInternals.fastIdentityHashCode with a dereference of an
  invalid memory address. This may manifest as a
  NullPointerException from J9VMInternals.fastIdentityHashCode or
  Object.hashCode. Note this issue only occurs when running a
  64-bit JVM with compressed references. 32-bit JVMs and 64-bit
  JVMs running without compressed references are not affected.
  .
  Stack Trace: N/A
  .
  

Local fix

• The problem can be worked around with
  -Xjit:dontInline={java/lang/J9VMInternals.fastIdentityHashCode*}
  ,exclude={java/lang/J9VMInternals.fastIdentityhashCode*}. Note
  that this can have a significant negative impact on throughput
  peformance. Another alternative is -Xnocompressedreferences, but
  this may require a large maximum heap size (-Xmx).
  

Problem summary

• J9VMInternals.fastIdentityHashCode(Object) incorrectly
  sign-extended the 32bit J9Class pointer when reading it from an
  object header in a
  compressedrefs VM. This can can cause crashes with i.e.
  InaccessibleReadAddress=FFFFFFFF999609D8
  

Problem conclusion

• The code has been modified to do an unsigned widening rather
  than a signed widening to ensure we generate the correct memory
  address.
  .
  This APAR will be fixed in the following Java Releases:
   8 SR5 FP11 (8.0.5.11)
  .
  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