[jboss-jira] [JBoss JIRA] (JASSIST-195) Verifier error with try-finally clause in Java 1.7

[John Brush (JIRA)]

John Brush created JASSIST-195:
----------------------------------

             Summary: Verifier error  with try-finally clause in Java 1.7
                 Key: JASSIST-195
                 URL: https://issues.jboss.org/browse/JASSIST-195
             Project: Javassist
          Issue Type: Bug
    Affects Versions: 3.17.1-GA
         Environment: Oracle Java 1.7 on Mac OS X
            Reporter: John Brush
            Assignee: Shigeru Chiba


After upgrading from Java 1.6 to Java 1.7 our unit tests failed due to the new verifier in 1.7 which requires a stack map. I fixed this issue by adding a call to the rebuildStackMap() method after instrumentation, but this caused a new problem to pop up in one particular instance:

	public int testInstrumentedCallInFinallyBlock( int i )
	{
		try
		{}
		catch ( Throwable t )
		{}
		finally
		{
			i = incByOne( i );
		}

		return i;
	}

This unit test results in the following exception:

java.lang.VerifyError: Stack map does not match the one at exception handler 9 in method xxx.StatementsTestComponent.testInstrumentedCallInFinallyBlock(I)I at offset 9

After some investigation, I noticed that the problem occurred independent of my instrumentation, simply as a result of loading the byte code with Javassist, invoking rebuildStackMap() and then trying to load it. The byte code for the above snippet looks as follows before invoking rebuildStackMap():

    Code:
      stack=2, locals=3, args_size=2
         0: aload_0       
         1: iload_1       
         2: invokespecial #3                  // Method incByOne:(I)I
         5: istore_1      
         6: goto          18
         9: astore_2      
        10: aload_0       
        11: iload_1       
        12: invokespecial #3                  // Method incByOne:(I)I
        15: istore_1      
        16: aload_2       
        17: athrow        
        18: iload_1       
        19: ireturn       
      Exception table:
         from    to  target type
             9    10     9   any
      StackMapTable: number_of_entries = 2
           frame_type = 73 /* same_locals_1_stack_item */
          stack = [ class java/lang/Throwable ]
           frame_type = 8 /* same */

Afterwards, it looks like this:

    Code:
      stack=2, locals=3, args_size=2
         0: aload_0       
         1: iload_1       
         2: invokespecial #23                 // Method incByOne:(I)I
         5: istore_1      
         6: goto          18
         9: nop           
        10: nop           
        11: nop           
        12: nop           
        13: nop           
        14: nop           
        15: goto          9
        18: iload_1       
        19: ireturn       
      Exception table:
         from    to  target type
             9    10     9   any
      StackMapTable: number_of_entries = 2
           frame_type = 249 /* chop */
          offset_delta = 9
           frame_type = 253 /* append */
             offset_delta = 8
        locals = [ class ch/shaktipat/saraswati/instrument/busicomp/StatementsTestComponent, int ]

Notice the modifications from lines 9-15: this is a result of Javassist's MapMaker.fixDeadcode() method. I assume that the verify error is a result of the exception table entry that refers to code which is no longer there. A possible fix would be to make sure that any exception handlers referring to dead code are removed in such cases. Personally, I would prefer that Javassist simply not modify the code if at all possible, or at least for such modifications to be optional (configurable).



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