IV71983: JAVA JIT - GC ASSERT MESSAGE IN JAVA 6 (26) AND 7.0

APAR status

• Closed as program error.

Error description

• Error Message: STDERR message including:
  
  0000000070863D00: Object neither in heap nor stack-allocated in
  thread <OSB>ACTIVE<CSB> Thread_Name
  
  0000000070863D00:  O-Slot=0000000072E9AE90
  0000000070863D00:  O-Slot value=0000000000000001
  0000000070863D00:  PC=000001001F36488C
  0000000070863D00:  framesWalked=2
  0000000070863D00:  arg0EA=0000000072EAAE30
  0000000070863D00:  walkSP=0000000072EA2E48
  0000000070863D00:  literals=0000000000000000
  0000000070863D00:  jitInfo=000001001E980B18
  0000000070863D00:  method=0000000072AE3EC8 (com/Class.method()V)
  (JIT)
  0000000070863D00:
  stack=0000000072E9DD98-0000000072EABD18
  Notes: The message will show that the "O-Slot" has a value that
  is out-side the limit of that stack defined on the "stack="
  line. The method must have the "(JIT)" text signifying that the
  method with the bad O-Slot is JIT compiled. If both these
  restrictions are not met then this APAR does not apply.
  .
  Stack Trace:
  {libj9prt26.so}{genSystemCoreUsingGencore}
  {libj9prt26.so}{j9dump_create}{libj9dmp26.so}{doSystemDump}
  {libj9dmp26.so}{protectedDumpFunction}
  {libj9prt26.so}{j9sig_protect}{libj9dmp26.so}{runDumpFunction}{l
  ibj9dmp26.so}{runDumpAgent}
  {libj9dmp26.so}{triggerDumpAgents}{libj9trc26.so}{twAssertion}
  {libj9ute26.so}{logTracePoint}{libj9ute26.so}{utsTraceV}{libj9tr
  c26.so}{j9Trace}
  {libj9gc26.so}{doStackSlot__31MM_ParallelScavengerRootScannerFPP
  8J9ObjectPvPCv}
  {libj9gc26.so}{stackSlotIterator__FP8J9JavaVMPP8J9ObjectPvP16J9S
  tackWalkStatePCv}
  {libj9gc26.so}{vmThreadStackDoOSlotIterator
  _FP10J9VMThreadP16J9StackWalkStatePP8J9ObjectPCv}
  {libj9jit26.so}{jitWalkRegisterMap}
  {libj9jit26.so}{jitWalkFrame}
  {libj9jit26.so}{jitWalkStackFrames}
  {libj9vm26.so}{walkStackFrames}
  {libj9gc26.so}{scanSlots__28GC_VMThreadStackSlotIteratorFP10J9VM
  ThreadT1PvPFP8J9JavaVMPP8J9ObjectPvP16J9StackWalkStatePCv_vbT5}
  {libj9gc26.so}{scanOneThread__14MM_RootScannerFP20MM_Environment
  ModronP10J9VMThreadPv}
  {libj9gc26.so}{scanThreads__14MM_RootScannerFP20MM_EnvironmentMo
  dron}
  {libj9gc26.so}{scanRoots__14MM_RootScannerFP20MM_EnvironmentModr
  on}
  {libj9gc26.so}{scavengeRoots__20MM_ParallelScavengerFP22MM_Envir
  onmentStandard}
  {libj9gc26.so}{workThreadGarbageCollect__20MM_ParallelScavengerF
  P22MM_EnvironmentStandard}
  {libj9gc26.so}{run__23MM_ParallelScavengeTaskFP20MM_EnvironmentM
  odron}
  .
  This problem does NOT exist in Java 6.0 or Java 5.0.Only Java 6
  (using the 26 J9 JVM) and Java 7.0 can encounter this problem.
  

Local fix

• The problem can be avoid by preventing the JIT from compiling
  the failing method:-Xjit:exclude={com/Class.method()V}The method
  name will be shown in the GC assert message as seen in this
  APAR. The method used in this work-around is just an example,
  you will need to use the method name that applies to your
  particular case (use the 'method=' line of the GC assert
  output).
  

Problem summary

• The JIT needs to describe to the GC what registers are saved
  and the offset into the stack frame where the saved registers
  are located. The GC uses this data along with a register object
  map to determine what objects are referenced by JIT compiled
  methods. The space given to hold the offset can overflow in
  extreme cases where the stack size is very large resulting in
  the GC obtaining an invalid object reference.
  

Problem conclusion

• The JIT was modified to abort any compiles where the register
  save offset overflows.
  .
  This APAR will be fixed in the following Java Releases:
     7    SR9 FP 10 (7.0.9.10)
     6 R1 SR8 FP7   (6.1.8.7)
  .
  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

• R260 PSY

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