IZ70114: JAVA JIT - INCORRECTLY STACK ALLOCATING OBJECTS

APAR status

• Closed as program error.

Error description

• Error Message: SIGSEV inside JIT compiled code, or in the
  Garbage Collector. Other types of symptoms are possible like
  crashing in the the interpreter or unexpected exceptions.
  .
  Stack Trace: N/A
  .
  For a method to trigger this problem it must be a rather large
  method (900 or more bytes of bytecodes) and it must have a high
  concentration of calls.
  

Local fix

• Use the following java command line option to avoid the problem:
  -Xjit:disableEscapeAnalysis
  Using this option may have a slight impact on performance, but
  in most cases it will be less then 1%.
  

Problem summary

• The JIT will incorrectly determine that it's safe to stack
  allocate an object. The object reference is then leaked into the
  heap and a crash can occur if the GC encounters this reference,
  the object is overwritten by future stack usage, or a truncated
  stack reference is used in a compressed references JVM. It's
  worth noting that this problem is rare and it is difficult to
  determine if a given issue is an example of this problem.
  

Problem conclusion

• This defect will be fixed in:
  6.0.0 SR8
  5.0.0 SR11 FP2
  .
  The JIT was modified so that it will handle this case by
  correctly determining when objects can not be stack allocated.
  .
  To obtain the fix:
  Install build 20100203 or later
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

  IZ69974

• APAR is sysrouted TO one or more of the following:

Fix information

• Fixed component name

  JAVA 5 JIT

• Fixed component ID

  620500124

Applicable component levels

• R500 PSN

     UP