Getting java.lang.VerifyError when adding try/catch to a method using CtMethod.insertAfter, if the method returns when the JVM stack is not empty - Inconsistent stack height 0 != 1, or Inconsistent stackmap frames at branch target -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Key: JASSIST-204 URL: https://issues.jboss.org/browse/JASSIST-204 Project: Javassist Issue Type: Bug Affects Versions: 3.17.0-GA, 3.18.0-GA Environment: Occurred on Windows with standard HotSpot JVM (1.6.0_24, 1.7.0_21, ..), also with IBM J9 JVM on AIX etc. Reporter: Dordoriko Beanie Assignee: Shigeru Chiba Labels: VerifyError, height, insertBefore, stack Attachments: popnopbug.zip After instrumenting certain classes with insertAfter(), I am consistently getting java.lang.VerifyError when trying to load the instrumented class(either "Inconsistent stack height 0 != 1" or "Inconsistent stackmap frames at branch target", depending on whether I'm on a newer 1.7 environment or an older one). The class was perfectly loadable prior to instrumentation, even though it exhibits a slightly unusual property that its return-type instructions are not necessarily executed when the stack is empty (not counting the return parameter, if applicable). The problem originally occurred with some class file that was apparently weaved by AspectJ 1.5.2a, but it was then reproduced by combining the following circumstances: 1) That the instrumented method has the "odd" property that it has an areturn/ireturn/return instruction which is invoked when the stack is not empty (when there are one or more values that were pushed onto the current frame and weren't popped). Note that I was unable to produce this with a freshly compiled .java source, so instead I took a simple .class file and changed one of the popping instructions to a nop instruction using a hex editor. 2) That the code added by insertAfter() contains a try/catch structure or something similar (which forces the stack height to be reset in case of catch). It is possible that this wasn't really necessary and that similar symptoms could occur by just having multiple return statements with different stack heights. When this happens, javassist replaces the original return-type instruction with a goto (when the stack height is N), but also adds a goto to the same label from the end of the catch clause (when the stack height is 0). runtest_modified_nop_java17.bat Exception in thread "main" java.lang.VerifyError: Inconsistent stackmap frames at branch target 35 in method com.test.HelloWorld.g()Ljava/lang/String; at offset 20 at java.lang.Class.getDeclaredMethods0(Native Method) at java.lang.Class.privateGetDeclaredMethods(Unknown Source) at java.lang.Class.getMethod0(Unknown Source) at java.lang.Class.getMethod(Unknown Source) at sun.launcher.LauncherHelper.getMainMethod(Unknown Source) at sun.launcher.LauncherHelper.checkAndLoadMain(Unknown Source) runtest_modified_nop_java12.bat Exception in thread "main" java.lang.VerifyError: (class: com/test/HelloWorld, method: g signature: ()Ljava/lang/String;) Inconsistent stack height 0 != 1 at java.lang.Class.getDeclaredMethods0(Native Method) at java.lang.Class.privateGetDeclaredMethods(Unknown Source) at java.lang.Class.getMethod0(Unknown Source) at java.lang.Class.getMethod(Unknown Source) at sun.launcher.LauncherHelper.getMainMethod(Unknown Source) at sun.launcher.LauncherHelper.checkAndLoadMain(Unknown Source)