IV87105: JAVA JIT PPC: CRASH EXECUTING BIGDECIMAL DFP OPERATIONS

APAR status

• Closed as program error.

Error description

• Error Message: SIGSEGV while executing in the following stack
  trace:
  0x0900000000ec7f48 {libj9vm26.so}{JBgetfield}
  <OSB>0x1002b7e0b00<CSB>
  0x0a000100006c3e2c {java/math/BigDecimal.isDFPZero} INT
  <OSB>0xc42fd6a0-0xc42fd768<CSB>
  .
  Stack Trace: The original report of this issue showed a crash in
  the interpreter executing the BigDecimal.isDFPZero() method, but
  other symptoms could occur such as a crash in a compiled form of
  a BigDecimal method or a method that uses BigDecimal routines
  and even corruption of Java heap objects.
  0x900000000ec7f48 {libj9vm26.so}{JBgetfield}
  <OSB>0x1002b7e0b00<CSB>
  0xa000100006c3e2c {java/math/BigDecimal.isDFPZero} INT
  <OSB>0xc42fd6a0-0xc42fd768<CSB>
  .
  The problem can occur only on PowerPC processors (AIX and Linux
  PPC) and only when executing DFP operations within the
  BigDecimal class. The problem is rare because it requires that
  there is a high degree of register pressure resulting in the JIT
  using GPR0, which the JIT avoids due to the fact the GPR0 is
  more restricted in how it can be used.
  

Local fix

• The problem can be avoided by using the following Java command
  line argument:
  -Xnodfpbd
  This option may effect performance in some rare cases, but in
  the general case the option has no effect on performance.
  

Problem summary

• The JIT compiler replaces some BigDecimal routines with routines
  that use the DFP hardware on PPC. These replacement routines
  failed to mark the target address register used for memory store
  operations so that GPR0 would not be used. This caused the JIT
  to shuffle registers (to avoid using GPR0) within a control flow
  path allowing for the register shuffle to be skipped under some
  conditional paths leaving the potential for bad values to be
  used later in the effected method.
  

Problem conclusion

• The JIT was modified such that it would correctly exclude GPR0
  for DFP store operations so that any register shuffling would be
  done outside any control flow paths.
  .
  This APAR will be fixed in the following Java Releases:
     6 R1 SR8 FP35  (6.1.8.35)
     7    SR9 FP60  (7.0.9.60)
     6    SR16 FP35 (6.0.16.35)
     7 R1 SR3 FP60  (7.1.3.60)
     8    SR3 FP11  (8.0.3.11)
  .
  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

• R260 PSY

     UP

• R600 PSY

     UP

• R130 PSY

     UP