IV07698: JAVA JIT PPC - RARE INCORRECT CALCULATION

APAR status

• Closed as program error.

Error description

• Error Message: An unexpected ArrayIndexOutOfBoundsException was
  thrown for the customer who reported this problem, but the
  problem is a incorrect calculation which can result in other
  symptoms depending on how the incorrect value is used.
  .
  Stack Trace: N/A
  .
  The problem only effects PowerPC (AIX32/64 and LinuxPPC32/64) on
  Java5, Java6 and Java6.0.1.
  

Local fix

• The problem can be avoided by excluding the compilation of the
  method that performs the incorrect calculation. If that method
  is known then the following java command line option can be used
  to avoid the problem:
  -Xjit:exclude={Package/Class.method*}
  Note: Excluding a method can degrade performance depending on
  how the excluded method is used by the application. In a typical
  application, excluding one methods has almost no effect on
  performance.
  

Problem summary

• When a 'left shift' (or power of 2 multiply) is performed along
  with an 'and' operation we can use the PowerPC 'rlwimn'
  instruction. This works for most cases, but if the 'and' bit
  mask as no bits set to 1, the instruction does not work as you
  might expect resulting an the 'and' operation not being
  performed as expected.
  

Problem conclusion

• This defect will be fixed in:
  6.0.1 SR2
  6.0.0 SR10
  5.0.0 SR13
  7.0.0 SR1
  .
  The JIT was modified to use a different instruction when doing a
  'shift' and an 'and' with a mask of 0.
  .
  To obtain the fix:
  Install build 20110921 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:

  IV07699

Fix information

• Fixed component name

  JIT

• Fixed component ID

  620700124

Applicable component levels

• R260 PSY

     UP

• R600 PSY

     UP