IV19701: USING SHARED CLASS WITH RE-TRANSFORMATION CAPABLE JVMTI AGENTS C AN RESULT IN SEGMENTATION FAULT OR JAVA.LANG.CLASSFORMATERROR

APAR status

• Closed as program error.

Error description

• Error Message: Segmentation Fault in libj9dyn26.so
  or
  java.lang.ClassFormatError exception
  .
  Stack Trace: j9bcutil_readClassFileBytes () from
  jre/lib/ppc/default/libj9dyn26.so
  lassFileParser::parseClassFile () from
  jre/lib/ppc/default/libj9dyn26.so
  ROMClassBuilder::buildROMClass () from
  jre/lib/ppc/default/libj9dyn26.so
  j9bcutil_buildRomClass () from jre/lib/ppc/default/libj9dyn26.so
  callDynamicLoader () from jre/lib/ppc/default/libj9dyn26.so
  internalLoadROMClass () from jre/lib/ppc/default/libj9dyn26.so
  reloadROMClasses () from jre/lib/ppc/default/libj9jvmti26.so
  redefineClassesCommon () from
  jre/lib/ppc/default/libj9jvmti26.so
  jvmtiRetransformClasses () from
  jre/lib/ppc/default/libj9jvmti26.so
  retransformClasses () from  jre/lib/ppc/libinstrument.so
  Java_sun_instrument_InstrumentationImpl_retransformClasses0 ()
  from jre/lib/ppc/libinstrument.so
  .
  

Local fix

• This problem can be prevented by disabling the shared class
  cache using -Xshareclasses:none. It can also be worked around by
  removing the re-transformation capable JVMTI agent.
  

Problem summary

• Problem is seen when the same shared class cache is used by
  multiple JVMs. In certain situations a JVM may store a
  re-transformed class in the shared cache such that one of the
  pointers in the class refers to the JVM's private memory. When
  another JVM tries to access this pointer, it may suffer a
  java.lang.ClassFormatError or a segmentation fault if that
  memory is not mapped in its address space.
  

Problem conclusion

• This defect will be fixed in:
  7.0.0 SR1
  6.0.1 SR2
  .
  The JVM has been updated to prevent the pointer in the shared
  cache class from referring to memory outside the cache.
  

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

  J9 COMMON CODE

• Fixed component ID

  620700127

Applicable component levels

• R260 PSY

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