IJ56768: JAVA JIT: A RARE FAILURE TO GENERATE A SIGN EXTEND ON Z

APAR status

• Closed as program error.

Error description

• Error Message: A SIGSEGV/OC4 is received when running JIT
  generated code
  .
  Stack Trace:
  {org/apache/.../BZip2CompressorInputStream.getAndMoveToFrontDeco
  de} JIT
  {org/apache/.../BZip2CompressorInputStream.initBlock} JIT
  ...
  The above stack trace is just an example as seen in the original
  report of the issue. The same issue could occur in the JIT
  compiled code for other methods.
  .
  The problem can happen on any 64bit J9 based JVM when running on
  IBM-Z hardware (zos or zLinux). The problem does not effect
  other platforms and it does not effect the 31bit Z J9 JVMs.
  

Local fix

• The issue can be avoided by setting the following environment
  variable before running java:
  TR_NSIGNEXTGRA=1
  This will prevent the JIT from attempting to reduce redundant
  sign extend instructions and therefore will have a small effect
  on performance of JIT generated code, maybe 1% overall for a
  typical application.
  

Problem summary

• In certain cases, the JIT compiler may generate an instruction
  to sign-extend a value into a register so that all subsequent
  uses of that value can skip additional sign-extension
  instructions. Once the value?s scope ends, the JIT may reuse the
  same register for a different value. In rare cases, the JIT
  incorrectly assumes the register is still sign-extended and
  fails to apply sign extension to the new value.
  

Problem conclusion

• The JIT was modified to correct the tracking of the sign
  extended state.
  https://github.com/eclipse-omr/omr/pull/8035
  .
  This APAR will be fixed in the following Releases:
  .
  IBM Semeru Runtimes
     25              25.0.2.0
     21              21.0.10.0
     17              17.0.18.0
     11              11.0.30.0
  IBM SDK, Java Technology Edition
     8    SR8 FP60  (8.0.8.60)
  .
  Downloads and supplementary documentation can be found at the
  following locations:
  - For non z/OS operating systems:
    - IBM Semeru Runtimes, Version 11 and later
      https://www.ibm.com/semeru-runtimes/downloads/
    - IBM SDK, Java Technology Edition, Version 8
      https://www.ibm.com/support/pages/java-sdk-downloads/
  - For the z/OS operating system:
    - Java SDK Products on z/OS
      https://www.ibm.com/support/pages/java-sdk-products-zos
  

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