IJ34933: JAVA/LANG/STRING.INDEXOF(STRING) MIGHT RETURN INCORRECT RESULT WHEN RUNNING ON A Z15 PROCESSOR

APAR status

• Closed as program error.

Error description

• Error Message: The java/lang/String.indexOf(String) API returns
  an index when it should return -1.
  .
  Stack Trace: N/A
  .
  The problem only occurs in the following circumstances:
  1. The application is running on a z15 processor with IBM Java
  8.0.6.0 or newer (SR6 or newer).
  2. The search string length is smaller than the underlying
  character array backing the string.
  3. The tail end of the pattern string contains characters which
  are found in the underlying character array past the end of the
  search string. For example if the search string is ?123456? of
  length 6, and is backed by an underlying character array
  <OSB>?1?, ?2?, ?3?, ?4?, ?5?, ?6?, ?7?, ?8?, ?9?<CSB> of length
  9, and the pattern we are looking for is ?5678". The pattern
  string should not be found in the search string, however the
  pattern string is found in the underlying character array.
  4. The pattern string must be greater than 8 characters.
  

Local fix

• This issue can be worked around using the -Xjit:disableZ15
  option. Note however that specifying this option will disable
  all JIT z15 exploitation which may affect performance.
  

Problem summary

• A logic error in the z15 exploitation of the SIMD Vector String
  Search instruction used to accelerate the
  java/lang/String.indexOf(String) API has been identified. The
  problem can only occur under a specific set of circumstances
  outlined previously.
  

Problem conclusion

• The JIT compiler has been updated to generate a correct assembly
  sequence to handle the problematic situation.
  .
  This APAR will be fixed in the following Java Releases:
     8    SR7       (8.0.7.0)
  .
  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