IJ47427: CRASH WITH ADJACENT MALFORMED OBJECTS

APAR status

• Closed as program error.

Error description

• Error Message: The JVM crashes while accessing a malformed
  object. Analysis of the crash will show the object came from an
  array of similarly malformed objects, adjacent to each other and
  likely overlapping.
  This problem can only happen on X and Z and with bytecode that
  was not generated by the Java compiler.
  .
  Stack Trace: The stack trace will depend on where the object is
  accessed from. The problem requires code from non-Java languages
  and this may be apparent from the call stack.
  .
  

Local fix

• The problem may be avoided by excluding the method which creates
  the array from compilation by the JIT. For example if the
  problem method was a.b.Class1.method1 then the following JVM
  command line option could be used:
  -Xjit:exclude={a/b/Class1.method1(*},dontInline={a/b/Class1.meth
  od1(*}
  Note that there can only be one Xjit option on the command line,
  so the above may need to be merged with any existing option that
  might be in use.
  

Problem summary

• The problem is caused by an optimization in the X and Z code
  generators for the multianewarray bytecode. In Java this
  bytecode is only used for arrays of dimension two or higher, but
  other languages or manually generated bytecodes may use
  multianewarray for one dimensional arrays. The code generated on
  X and Z incorrectly assumes a minimum of two dimensions with the
  potential for malformed objects as a result.
  

Problem conclusion

• The evaluator for multianewarray on X and Z was updated to check
  the dimensionality of the array before applying the problem
  optimization. For more detail see
  https://github.com/eclipse-openj9/openj9/issues/17360
  .
  This APAR will be fixed in the following Releases:
  .
  IBM SDK, Java Technology Edition
     8    SR8 FP11  (8.0.8.11)
  .
  Contact your IBM Product's Service Team for these Service
  Refreshes and Fix Packs.
  For those running stand-alone, information about the available
  maintenance can be found at:
             https://www.ibm.com/support/pages/java-sdk
  

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