IJ32096: UNEXPECTED EXCEPTIONS/BEHAVIOUR WHEN SHARED CLASSES AND AOT COMPILATION IS ENABLED

APAR status

• Closed as program error.

Error description

• Error Message: N/A
  .
  Stack Trace: N/A
  .
  This issue can occur on any Java platform that uses OpenJ9
  runtime. The problem can only occur in an application where
  multiple classes with same class hierarchy are loaded by
  different class-loaders while using shared classes and AOT.
  

Local fix

• Using the AOT option, -Xaot:maxCheckcastProfiledClassTests=0
  will disable the heuristic that causes this behaviour in AOT
  compiled code while causing a minor performance penalty for AOT
  compiled methods. If an AOT compiled method becomes hot, it will
  get recompiled as a normal JIT compile where this problem is not
  possible and the work-around option has no effect.
  

Problem summary

• In AOT/JIT compiled code, we generate series of inlined tests
  for checkcast/InstanceOf Bytecodes. One of the tests in the
  sequence uses the profiled data for that particular sites and
  based on the relationship between the classes in profiled data
  for that site and the cast class, it generates tests to get the
  result of the checkcast/instanceOf quickly. In case of AOT
  compiled code, we were missing validation information that
  verifies the relationship between profiled class and the cast
  class when AOT code is loaded from shared class cache, without
  which the generated test could result in an unexpected code path
  to be executed.
  

Problem conclusion

• Compiler code has been updated to disable the use of profiled
  class data for checkcast/instanceOf code, when Shared Class
  Cache is enabled and it is generating AOT code.
  .
  This APAR will be fixed in the following Java Releases:
     8    SR6 FP31  (8.0.6.31)
  .
  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:

Fix information

• Fixed component name

  JIT

• Fixed component ID

  620700124

Applicable component levels