IJ14950: INTERMITTENT CRASH IN JAVA JIT COMPILER

APAR status

• Closed as program error.

Error description

• Error Message: A segmentation error in code that has been
  compiled by the Java JIT compiler is reported intermittently.
  .
  Stack Trace: N/A
  .
  

Local fix

• The problem can be worked around by specify the option
  -Xjit:disableEscapeAnalysis.  Specifying this option might have
  an effect on program performance.
  

Problem summary

• One optimization of the Java JIT compiler is known as Escape
  Analysis.  Under this optimization, the compiler identifies Java
  objects whose duration is brief, and it allocates them on the
  run-time stack rather than the Java heap in order to improve the
  run-time performance of the program.  Such an object might be
  allocated on the run-time stack as a contiguous object, or if
  the entire object is not needed, as the individual fields of the
  original object.
  For each object whose individual fields will be allocated on the
  run-time stack, Escape Analysis also analyzes the generated code
  for any checks that the compiler might have generated of whether
  the original object was an instance of a class that overrides
  the finalize() method inherited from java.lang.Object.  Such a
  check is not needed for an object whose individual fields will
  be allocated on the run-time stack as the object as a whole
  doesn't actually exist - Escape Analysis attempts to remove
  those checks.
  In some circumstances, however, an optimization might have been
  applied to the code that checks whether an object was an
  instance of a class that overrides the finalize() method,
  causing Escape Analysis to fail to recognize and remove that
  check.
  The check depends on the address of the object, which is now a
  null reference due to the optimization, triggering the crash.
  

Problem conclusion

• The problem was fixed by adjusting the pattern Escape Analysis
  uses to recognize generated code that checks whether an object
  was an instance of a class that overrides the finalize() method.
   This change to the pattern allows Escape Analysis to recognize
  the check regardless of whether an optimization was applied to
  that check.
  .
  This APAR will be fixed in the following Java Releases:
     8    SR5 FP31  (8.0.5.31)
  .
  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