IJ50878: JAVA JIT: SEGV IN ARRAY COPY FOR STRINGBUFFER OR STRINGBUILDER ON POWER OR AARCH64

APAR status

• Closed as program error.

Error description

• Error Message: A SIG_SEGV is received when executing an
  array-copy in StringBuffer.append().
  .
  Stack Trace: {libj9jit29.so}{__codeForShortArrayCopy}
  {libj9jit29.so}{__arrayCopy}
  {libj9jit29.so}{__arrayCopy_dp}
  {java/lang/StringBuffer.append} JIT
  {org/apache/log4j/helpers/PatternParser$LiteralPatternConverter.
  format} JIT
  {org/apache/log4j/WriterAppender.subAppend} JIT
  {org/apache/log4j/Category.forcedLog} JIT
  The StringBuffer.append() is likely going to be on the stack and
  arrayCopy() JIT helper routines will be at the top of the stack.
  .
  This problem can only occur on systems where the architecture
  employs weak memory coherency. This mean POWER or AArch64. The
  issue can not occur on x86 or IBM-Z for example. The problem is
  extremely intermittent since the timing window is very small and
  it can only occur when new objects are exposed to more then one
  thread without some barrier like synchronization or the use of
  volatile fields.
  

Local fix

• The problem can be avoided by preventing the JIT from compiling
  the StringBuffer/StringBuilder methods. This will have some
  affect on performance but the extent of that effect depends on
  how important the performance of StringBuffer/StringBuilder
  methods are to the overall performance of the application.
  -Xjit:exclude={*/StringBuffer.*<PIPE>*/StringBuilder.*},dontInli
  ne={*/StringBuffer.*<PIPE>*/StringBuilder.*}
  

Problem summary

• The JIT compiler is removing NULL-CHECKS from
  StringBuffer/StringBuilder methods which can in rare cases
  result in a crash if the java application is exposing new object
  instances to other threads without using something to enforce
  store ordering on systems with weak memory coherency.
  

Problem conclusion

• The JIT was modified so that a store-store barrier is added
  after running the constructor of StringBuffer/StringBuilder
  objects on systems with weak memory coherency.
  .
  This APAR will be fixed in the following Releases:
  .
  IBM Semeru Runtimes
     11              11.0.24.0
     17              17.0.12.0
  IBM SDK, Java Technology Edition
     8    SR -      (8.0.-.0)
  .
  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