Here's the code:

  public long getSize() {
    return Oop.alignObjectSize(getHeaderSize() + Oop.alignObjectOffset(getVtableLen()) +
                               Oop.alignObjectOffset(getItableLen()) + Oop.alignObjectOffset(getNonstaticOopMapSize()));
  }

Issue #1: getSize() is suppose to return the number of bytes. getVtableLen(), getItableLen(), and getNonstaticOopMapSize() all return the number or words. Their values need to be scaled by the word size, but aren't.

Issue #2: If the InstanceKlass is an interface or an anonymous class, and extra word of memory needs to be added to the size.

Issue #3: There is no test for this code.

Here's how I showed it isn't working properly:

bash-4.1$ /java/re/jdk/9/promoted/latest/binaries/linux-x64/bin/java -XX:+UnlockDiagnosticVMOptions -version
java version "9-ea"
Java(TM) SE Runtime Environment (build 9-ea+96-2015-12-09-185335.javare.4030)
Java HotSpot(TM) 64-Bit Server VM (build 9-ea+96-2015-12-09-185335.javare.4030, mixed mode)

bash-4.1$ /java/re/jdk/9/promoted/latest/binaries/linux-x64/bin/java -XX:+UnlockDiagnosticVMOptions -cp /local/export/tests/ HelloWorld -wait &
[1] 28623
Hello world.

# Note for the list of classes in the jcmd output below, I pruned out all but the 3 I later use with CLHSDB
bash-4.1$ /local/ws/jdk9/hs-rt/build/linux-x86-normal-clientANDserverANDminimal1-slowdebug/jdk/bin/jcmd HelloWorld GC.class_stats VTab,ITab,OopMap,KlassBytes
28623:
Index Super KlassBytes VTab ITab OopMap ClassName
   37 -1 496 40 16 0 java.lang.Object
   55 383 1384 472 464 8 java.util.Vector
  517 384 936 248 232 16 sun.util.PreHashedMap
Index Super KlassBytes VTab ITab OopMap ClassName

bash-4.1$ /java/re/jdk/9/promoted/latest/binaries/linux-x64/bin/java sun.jvm.hotspot.CLHSDB 28745
Attaching to process 28745, please wait...
hsdb> jseval "sapkg.utilities.SystemDictionaryHelper.findInstanceKlass('java.lang.Object').getSize();"
456 <--- Should be 496
hsdb> jseval "sapkg.utilities.SystemDictionaryHelper.findInstanceKlass('java.util.Vector').getSize();"
576 <--- Should be 1384
hsdb> jseval "sapkg.utilities.SystemDictionaryHelper.findInstanceKlass('sun.util.PreHashedMap').getSize();"
512 <--- Should be 936