ASM中的Java方法参数值

本文介绍了ASM中的Java方法参数值的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我试图获取Java程序方法参数的值。 我正在使用ASM来检测字节码并获取这些值。 但是，我遇到了一些麻烦。

I am trying to get the values of a Java program's method's parameters. I am using ASM to instrument the bytecode and getting these values. However, I'm running into some troubles.

这是用于检测代码的visitCode（）方法。 它正在做的是：

Here is the visitCode() method used to instrument the code. What it is doing is :

创建一个空数组来存储收集的参数。

对于每个参数，将其值加载到数组中。

将此数组发送到我的代理的OnMethodEntry方法（将使用值）。

。

@Override public void visitCode() { int paramLength = paramTypes.length; // Create array with length equal to number of parameters mv.visitIntInsn(Opcodes.BIPUSH, paramLength); mv.visitTypeInsn(Opcodes.ANEWARRAY, "java/lang/Object"); mv.visitVarInsn(Opcodes.ASTORE, paramLength); // Fill the created array with method parameters int i = 0; for (Type tp : paramTypes) { mv.visitVarInsn(Opcodes.ALOAD, paramLength); mv.visitIntInsn(Opcodes.BIPUSH, i); if (tp.equals(Type.BOOLEAN_TYPE) || tp.equals(Type.BYTE_TYPE) || tp.equals(Type.CHAR_TYPE) || tp.equals(Type.SHORT_TYPE) || tp.equals(Type.INT_TYPE)) mv.visitVarInsn(Opcodes.ILOAD, i); else if (tp.equals(Type.LONG_TYPE)) { mv.visitVarInsn(Opcodes.LLOAD, i); i++; } else if (tp.equals(Type.FLOAT_TYPE)) mv.visitVarInsn(Opcodes.FLOAD, i); else if (tp.equals(Type.DOUBLE_TYPE)) { mv.visitVarInsn(Opcodes.DLOAD, i); i++; } else mv.visitVarInsn(Opcodes.ALOAD, i); mv.visitInsn(Opcodes.AASTORE); i++; } // Load id, class name and method name this.visitLdcInsn(new Integer(this.methodID)); this.visitLdcInsn(this.className); this.visitLdcInsn(this.methodName); // Load the array of parameters that we created this.visitVarInsn(Opcodes.ALOAD, paramLength); mv.visitMethodInsn(Opcodes.INVOKESTATIC, "jalen/MethodStats", "onMethodEntry", "(ILjava/lang/String;Ljava/lang/String;[Ljava/lang/Object;)V"); super.visitCode(); }

但是，当显然该方法有多个参数时，这不起作用。

However, this is not working when apparently the method have more than one parameter.

获得的类文件显示如下内容：

The class file obtained shows things like this :

static void moveDisk(char arg0, char arg1, PrintStream arg2) { Object[] arrayOfObject = new Object[3]; arrayOfObject[0] = ???; arrayOfObject[1] = ???; Object localObject; arrayOfObject[2] = localObject; MethodStats.onMethodEntry(5, "hanoi/TowersOfHanoi", "moveDisk", arrayOfObject);

创建2个本地对象而不是加载参数。

Where 2 local objects are created instead of loading the parameters.

字节码没有显示任何奇怪的东西：

The bytecode doesn't show anything weird :

static void moveDisk(char, char, java.io.PrintStream); Code: 0: bipush 3 2: anewarray #4 // class java/lang/Object 5: astore_3 6: aload_3 7: bipush 0 9: iload_0 10: aastore 11: aload_3 12: bipush 1 14: iload_1 15: aastore 16: aload_3 17: bipush 2 19: aload_2 20: aastore 21: ldc #118 // int 5 23: ldc #12 // String hanoi/TowersOfHanoi 25: ldc #119 // String moveDisk 27: aload_3 28: invokestatic #19 // Method jalen/MethodStats.onMethodEntry:(ILjava/lang/String;Ljava/lang/String;[Ljava/lang/Object;)V

最后，显示的错误是（当使用-noverify时：

And finally, the error showed is (when using -noverify):

param: [Ljava.lang.String;@420e54f3 Exception in thread "Jalen Agent" java.lang.NullPointerException at hanoi.TowersOfHanoi.solveHanoi(TowersOfHanoi.java) at hanoi.TowersOfHanoi.main(TowersOfHanoi.java:29)

否则，它是：

Exception in thread "Jalen Agent" java.lang.VerifyError: (class: hanoi/TowersOfHanoi, method: moveDisk signature: (CCLjava/io/PrintStream;)V) Expecting to find object/array on stack at java.lang.Class.getDeclaredMethods0(Native Method) at java.lang.Class.privateGetDeclaredMethods(Class.java:2442) at java.lang.Class.getMethod0(Class.java:2685) at java.lang.Class.getMethod(Class.java:1620) at sun.launcher.LauncherHelper.getMainMethod(LauncherHelper.java:492) at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:484)

通常，这应该工作，因为我只是从堆栈帧加载信息。 我还尝试检查静态&非静态方法（截至此处解释的堆栈： www.artima/insidejvm/ed2/jvm8 .html ），但仍然没有成功。

Normally, this should rather work as I am just loading information from the stack frame. I tried also to check static & non static methods (as of the stack explained here : www.artima/insidejvm/ed2/jvm8.html), but still with no success.

有关为什么会发生这种情况的想法，或者可能是解决方案的想法？

Any idea on why this is happening, or possibly an idea of a solution ?

谢谢：）

编辑：

现在正在装箱原始类型（感谢下面的int3的建议:)）。以下是visitCode（）方法的工作代码：

It is now working when boxing up primitive types (thanks to suggestions by int3 below :) ). Here is the working code of visitCode() method :

@Override public void visitCode() { int paramLength = paramTypes.length; // Create array with length equal to number of parameters mv.visitIntInsn(Opcodes.BIPUSH, paramLength); mv.visitTypeInsn(Opcodes.ANEWARRAY, "java/lang/Object"); mv.visitVarInsn(Opcodes.ASTORE, paramLength); // Fill the created array with method parameters int i = 0; for (Type tp : paramTypes) { mv.visitVarInsn(Opcodes.ALOAD, paramLength); mv.visitIntInsn(Opcodes.BIPUSH, i); if (tp.equals(Type.BOOLEAN_TYPE)) { mv.visitVarInsn(Opcodes.ILOAD, i); mv.visitMethodInsn(Opcodes.INVOKESTATIC, "java/lang/Boolean", "valueOf", "(Z)Ljava/lang/Boolean;"); } else if (tp.equals(Type.BYTE_TYPE)) { mv.visitVarInsn(Opcodes.ILOAD, i); mv.visitMethodInsn(Opcodes.INVOKESTATIC, "java/lang/Byte", "valueOf", "(B)Ljava/lang/Byte;"); } else if (tp.equals(Type.CHAR_TYPE)) { mv.visitVarInsn(Opcodes.ILOAD, i); mv.visitMethodInsn(Opcodes.INVOKESTATIC, "java/lang/Character", "valueOf", "(C)Ljava/lang/Character;"); } else if (tp.equals(Type.SHORT_TYPE)) { mv.visitVarInsn(Opcodes.ILOAD, i); mv.visitMethodInsn(Opcodes.INVOKESTATIC, "java/lang/Short", "valueOf", "(S)Ljava/lang/Short;"); } else if (tp.equals(Type.INT_TYPE)) { mv.visitVarInsn(Opcodes.ILOAD, i); mv.visitMethodInsn(Opcodes.INVOKESTATIC, "java/lang/Integer", "valueOf", "(I)Ljava/lang/Integer;"); } else if (tp.equals(Type.LONG_TYPE)) { mv.visitVarInsn(Opcodes.LLOAD, i); mv.visitMethodInsn(Opcodes.INVOKESTATIC, "java/lang/Long", "valueOf", "(J)Ljava/lang/Long;"); i++; } else if (tp.equals(Type.FLOAT_TYPE)) { mv.visitVarInsn(Opcodes.FLOAD, i); mv.visitMethodInsn(Opcodes.INVOKESTATIC, "java/lang/Float", "valueOf", "(F)Ljava/lang/Float;"); } else if (tp.equals(Type.DOUBLE_TYPE)) { mv.visitVarInsn(Opcodes.DLOAD, i); mv.visitMethodInsn(Opcodes.INVOKESTATIC, "java/lang/Double", "valueOf", "(D)Ljava/lang/Double;"); i++; } else mv.visitVarInsn(Opcodes.ALOAD, i); mv.visitInsn(Opcodes.AASTORE); i++; } // Load id, class name and method name this.visitLdcInsn(new Integer(this.methodID)); this.visitLdcInsn(this.className); this.visitLdcInsn(this.methodName); // Load the array of parameters that we created this.visitVarInsn(Opcodes.ALOAD, paramLength); mv.visitMethodInsn(Opcodes.INVOKESTATIC, "jalen/MethodStats", "onMethodEntry", "(ILjava/lang/String;Ljava/lang/String;[Ljava/lang/Object;)V"); super.visitCode(); }

推荐答案

您正在使用 aastore 将 char 存储到对象数组中，这是一个类型错误。 aastore 应仅用于存储对象和数组，这可能就是错误说堆栈上预期的对象/数组的原因。应使用 castore 将字符存储在char数组中。但是，由于您希望这适用于任意签名，您可能希望将基元类型打包成对象，然后您可以使用 aastore - 例如 char 应该装在 java.lang.Character 对象中。

You are using aastore to store a char into an object array, which is a type error. aastore should only be used to store objects and arrays, which is probably why the error says 'expected object/array on stack'. Characters should be stored in a char array using castore. However, since you want this to work for arbitrary signatures, you'll probably want to box up the primitive types into objects which you can then use aastore upon -- e.g. char should be boxed up in a java.lang.Character object.