IV88842: JAVA 6.1/7.0 JIT: UNALIGNED ALLOCATIONS CAUSES BAD MEMORY READS FOR FIELDS CROSSING A CACHE LINE BOUNDARY.

APAR status

• Closed as program error.

Error description

• Error Message: A SIGSEGV inside the JIT compiler.
  .
  Stack Trace:
  {libj9jit26.so}{findFieldInfo__31TR_PersistentClassInfoForFields
  FP14TR_CompilationRP7TR_Nodeb}
  {libj9jit26.so}{constrainIaload__FP19TR_ValuePropagationP7TR_Nod
  e}
  {libj9jit26.so}{launchNode__19TR_ValuePropagationFP7TR_NodeT1i}
  {libj9jit26.so}{constrainChildren__FP19TR_ValuePropagationP7TR_N
  ode}
  {libj9jit26.so}{launchNode__19TR_ValuePropagationFP7TR_NodeT1i}
  {libj9jit26.so}{processTrees__19TR_ValuePropagationFP10TR_TreeTo
  pT1}
  {libj9jit26.so}{processBlock__25TR_GlobalValuePropagationFP24TR_
  StructureSubGraphNodebT2}
  {libj9jit26.so}{processStructure__25TR_GlobalValuePropagationFP2
  4TR_StructureSubGraphNodebT2}
  .
  This problem can not occur in Java versions prior to 6.1 (Java 6
  using J9 r26) due to the lack of multiple compiler threads and
  the problem was inadvertently fixed in Java 7.1 (Java 7 using J9
  27) and higher in order to avoid a incompatibility with newer
  GCC compilers. The problem can only occur on 64bit platforms.
  

Local fix

• The problem can only be avoided by disabling the JIT.
  -Xint
  

Problem summary

• The JIT compilers memory manager could respond to allocations
  requests with 4 byte aligned memory address on 64bit platforms.
  This could cause a problem in very rare cases when a pointer is
  stored in memory and that pointer is straddling a cache line
  boundary.
  

Problem conclusion

• The JIT memory allocation routine was modified so the it will
  always return 8byte aligned memory addresses.
  .
  This APAR will be fixed in the following Java Releases:
     6 R1 SR8 FP35  (6.1.8.35)
     7    SR9 FP60  (7.0.9.60)
  .
  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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