IV14296: JAVA JIT - EXECUTING UNLOADED METHODS

APAR status

• Closed as program error.

Error description

• Error Message: Crash in the VM's getOriginalROMMethod() method
  when executing getStackTrace()
  Other symptoms are possible as the problem allows the execution
  of code from an unloaded method using a 'this' pointer of an
  incompatible type.
  .
  Stack Trace: {libj9vm24.so}{getOriginalROMMethod}
  
  {libjclscar_24.so}{getStackTrace}
  {libjclscar_24.so}{java_lang_J9VMInternals_getStackTrace}
  .
  The problem can only occur on PowerPC (AIX or LinuxPPC). Only
  the "default" 64bit JVM can experience a crash due to this
  problem. If the -Xcompressedrefs option was used then the
  problem can not possibly result in a crash or any other issue.
  

Local fix

• The only way to avoid the problem is to use the compressedrefs
  JVM or the 32bit JVM. The compressedrefs JVM can be used by
  specifying the command line argument -Xcompressedrefs. Using the
  compressedrefs JVM is very unlikely to cause a performance
  regression, in fact, it is likely to show a performance
  improvement over the default 64bit JVM.
  

Problem summary

• The JIT fails to properly patch a reference to a class that is
  being unloaded. If the memory space used by the unloaded class
  is reused to load a new class, and the new class is of the same
  class hierarchy as the unloaded class, then the code of the
  unloaded class could be executed when a reference to an object
  of the new class is passed to a JIT compiled method who had
  inlined a method from the unloaded class.
  

Problem conclusion

• This defect will be fixed in:
  
  6.0.1 SR2
  6.0.0 SR11
  7.0.0 SR1
  .
  The JIT was modified so that it correctly patches class
  references such that it is impossible for a patched reference to
  be mistaken for a class that was loaded in the same memory space
  as the unloaded class.
  

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

• R260 PSY

     UP

• R600 PSY

     UP