IJ12293: JAVA JIT PPC: CRASH IN JITED CODE ON POWER9 CPUS

APAR status

• Closed as program error.

Error description

• Error Message: SIGSEGV in libj9vm29.so
  .
  Stack Trace: N/A
  .
  The problem could appear in many different ways but the most
  likely symptoms include a crash in libj9vm29.so, libj9jit29.so
  or a crash inside JIT compiled code. A crash in the GC and
  incorrect behaviour is also possible.
  The issue is only possible on PPC platforms (power Linux or AIX)
  and only when running on POWER9 CPUs. When running on POWER8 or
  older CPUs this problem is not possible!
  Only Java 8 (8.0.5.0 through 8.0.5.26) can encounter this
  problem as 8.0.5.0 is the first version of Java to make use of
  POWER9 instructions.
  

Local fix

• The problem can be avoided by preventing the JIT got using the
  "move register peep holes" optimization. This can be done by
  setting the following environment variable before starting the
  JVM.
  export TR_DisableMRPeepholes=1
  You can confirm that this option is set correctly and has taken
  effect by looking for the following message in the stderr output
  of the JVM:
  "JIT: env var TR_DisableMRPeepholes is set to 1"
  The performance effect of using this options will be minor.
  

Problem summary

• The JIT attempts to remove "move register (mr)" instructions by
  rewriting instructions that make use of the mr target to use the
  mr source instead. The new 3-source type instructions in POWER9
  were not being correctly handled by this optimization allowing
  for these instruction to continue using the mr target register
  when they should have been rewritten to use the mr source
  register instead.
  

Problem conclusion

• The JIT was modified such that the move register peephole
  optimization now correctly handles POWER9 type 3-source
  instructions.
  .
  This APAR will be fixed in the following Java Releases:
     8    SR5 FP30  (8.0.5.30)
  .
  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