IZ96498: JAVA5/6 JIT-INCORRECT REMOVAL OF ARRAY BOUNDS CHECK WHEN USING B YTE OR SHORT INDEX VARIABLE

APAR status

• Closed as program error.

Error description

• Error Message: SIGSEGV executing JIT compiled code.
  Other symptoms are possible because of Java heap corruption due
  to this error.
  .
  Stack Trace: N/A
  .
  The problem can only occur when using a byte or short variable
  as the array index and only if the upper limit of the loop is
  larger than can be represented by the variable (e.g. >127 for
  byte or >32767 for short).
  

Local fix

• The problem can be avoided by using the following Java command
  line option:
  -Xjit:disableLoopVersioner
  Using the above option will degrade performance between 5 and 10
  percent, depending on the application.
  

Problem summary

• The JIT was removing bound checks when there is a possibility
  that the array index will overflow to a negative value,
  resulting reading or writing to negative offsets.
  

Problem conclusion

• This defect will be fixed in:
  5.0.0 SR13
  6.0.0 SR10
  .
  The JIT was modified to prevent this problem from occuring.
  .
  To obtain the fix:
  Install build 20110323 or later
  

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:

  IZ96499 IZ98871

Fix information

• Fixed component name

  JAVA 5 JIT

• Fixed component ID

  620500124

Applicable component levels

• R500 PSN

     UP