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

[Shigeru Chiba (JIRA)]

    [ https://issues.jboss.org/browse/JASSIST-195?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12775196#comment-12775196 ] 

Shigeru Chiba commented on JASSIST-195:
---------------------------------------

This would be a bug of MapMaker.fixDeadcode().
                
> 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:
> {code}
> 	public int testInstrumentedCallInFinallyBlock( int i )
> 	{
> 		try
> 		{}
> 		catch ( Throwable t )
> 		{}
> 		finally
> 		{
> 			i = incByOne( i );
> 		}
> 		return i;
> 	}
> {code} 
> 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}
>     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 */
> {code}
> Afterwards, it looks like this:
> {code}
>     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 ]
> {code}
> 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).
> BTW: my only workaround for the time being is to force the 1.7 JVM to use the old verifier with -XX:-UseSplitVerifier.

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