FULL PRODUCT VERSION :


A DESCRIPTION OF THE PROBLEM :
Test the next program (a monitored object is not initizlied) on HotSpot and IBM's J9. J9 throw out a verifier error, while HotSpot does not. It seems that HotSpot's verifier forgets to check whether a monitored object is initialized.

Besides, I tested the program on HotSpot for Java 9. The problem is also there.





THE PROBLEM WAS REPRODUCIBLE WITH -Xint FLAG: Did not try

THE PROBLEM WAS REPRODUCIBLE WITH -server FLAG: Did not try

EXPECTED VERSUS ACTUAL BEHAVIOR :
Throws a verify error, similar to J9's report.

Exception in thread "main" java.lang.VerifyError: JVMVRFY012 stack shape inconsistent; class=Search, method=main([Ljava/lang/String;)V, pc=6
Exception Details:
  Location:
    Search.main([Ljava/lang/String;)V @6: JBmonitorenter
  Reason:
    Type 'uninitialized' (current frame, stack[1]) is not assignable to 'java/lang/Object'
  Current Frame:
    bci: @6
    flags: { }
    locals: { 'Search', '[Ljava/lang/String;' }
    stack: { 'uninitialized', 'uninitialized' }
at T.main(T.java:4)



REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
public class Search
  minor version: 0
  major version: 52
  flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
   #1 = Utf8 Search
   #2 = Class #1 // Search
   #3 = Utf8 java/lang/Object
   #4 = Class #3 // java/lang/Object
   #5 = Utf8 <clinit>
   #6 = Utf8 ()V
   #7 = Utf8 <init>
   #8 = NameAndType #7:#6 // "<init>":()V
   #9 = Methodref #4.#8 // java/lang/Object."<init>":()V
  #10 = Utf8 main
  #11 = Utf8 ([Ljava/lang/String;)V
  #12 = Utf8 java/lang/Exception
  #13 = Class #12 // java/lang/Exception
  #14 = Utf8 Code
  #15 = Utf8 Exceptions
{
  public static {};
    descriptor: ()V
    flags: ACC_PUBLIC, ACC_STATIC
    Code:
      stack=0, locals=0, args_size=0
         0: return

  public Search();
    descriptor: ()V
    flags: ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
         0: aload_0
         1: invokespecial #9 // Method java/lang/Object."<init>":()V
         4: return

  public void main(java.lang.String[]) throws java.lang.Exception;
    descriptor: ([Ljava/lang/String;)V
    flags: ACC_PUBLIC
    Code:
      stack=3, locals=2, args_size=2
         0: new #2 // class Search
         3: dup
         4: aload_0
         5: monitorenter
         6: monitorenter
         7: monitorexit
         8: aload_0
         9: monitorexit
        10: return
    Exceptions:
      throws java.lang.Exception
}
---------- END SOURCE ----------