Question

我正在使用ASM 4来动态生成一些类。一切都很顺利，直到我生成代码来进行异常处理。生成的字节码位于底部。这是我得到的错误：

java.lang.VerifyError: Instruction type does not match stack map in method some.eval.ToEvaluate$0.apply()Ljava/lang/Object; at offset 44
at java.lang.Class.getDeclaredConstructors0(Native Method)
at java.lang.Class.privateGetDeclaredConstructors(Class.java:2404)
at java.lang.Class.getConstructor0(Class.java:2714)
at java.lang.Class.newInstance0(Class.java:343)
at java.lang.Class.newInstance(Class.java:325)
    ...

这是字节码：

// Compiled from com/pkg/some/Source.java (version 1.7 : 51.0, super bit)
public class some.eval.ToEvaluate$0 extends com.pkg.lang.Lambda0 {

  // Method descriptor #7 ()V
  // Stack: 1, Locals: 1
  public ToEvaluate$0();
    0  aload_0 [this]
    1  invokespecial com.pkg.lang.Lambda0() [9]
    4  return
      Line numbers:
        [pc: 0, line: 1]
        [pc: 0, line: 2]
        [pc: 4, line: 3]
      Local variable table:
        [pc: 0, pc: 5] local: this index: 0 type: new some.eval.ToEvaluate(){}

  // Method descriptor #13 ()Ljava/lang/Object;
  // Stack: 5, Locals: 3
  public java.lang.Object apply();
     0  getstatic com.pkg.some.Primitives.equal : com.pkg.lang.Lambda [19]
     3  checkcast com.pkg.lang.Lambda2 [21]
     6  getstatic com.pkg.some.Primitives.divide : com.pkg.lang.Lambda [26]
     9  checkcast com.pkg.lang.Lambda2 [21]
    12  ldc2_w <Long 1> [27]
    15  invokestatic java.lang.Long.valueOf(long) : java.lang.Long [34]
    18  ldc2_w <Long 0> [35]
    21  invokestatic java.lang.Long.valueOf(long) : java.lang.Long [34]
    24  invokevirtual com.pkg.lang.Lambda2.apply(java.lang.Object, java.lang.Object) : java.lang.Object [39]
    27  astore_1 [v1]
    28  goto 44
    31  astore_2 [e]
    32  new some.lambda.ToRun$1 [41]
    35  dup
    36  invokespecial some.lambda.ToRun$1() [42]
    39  aload_2 [e]
    40  invokevirtual com.pkg.lang.Lambda1.apply(java.lang.Object) : java.lang.Object [47]
    43  astore_1
    44  ldc2_w <Long -1> [48]
    47  invokestatic java.lang.Long.valueOf(long) : java.lang.Long [34]
    50  invokevirtual com.pkg.lang.Lambda2.apply(java.lang.Object, java.lang.Object) : java.lang.Object [39]
    53  areturn
      Exception Table:
        [pc: 6, pc: 28] -> 31 when : java.lang.Throwable
      Line numbers:
        [pc: 6, line: 50]
        [pc: 12, line: 21]
        [pc: 18, line: 21]
        [pc: 31, line: 51]
        [pc: 32, line: 52]
        [pc: 44, line: 54]
        [pc: 44, line: 21]
      Local variable table:
        [pc: 0, pc: 54] local: this index: 0 type: new some.eval.ToEvaluate(){}
        [pc: 28, pc: 31] local: v1 index: 1 type: java.lang.Object
        [pc: 32, pc: 44] local: e index: 2 type: java.lang.Throwable
        [pc: 44, pc: 44] local: v2 index: 1 type: java.lang.Object
      Stack map table: number of frames 2
        [pc: 31, same_locals_1_stack_item, stack: {java.lang.Throwable}]
        [pc: 44, full, stack: {com.pkg.lang.Lambda2}, locals: {some.eval.ToEvaluate$0, java.lang.Object}]
}

我使用ASMifier开始：

public static Object trycatch(Object test, Lambda1 handler) {
    Object v;
    try {
        v = test;
    } catch (Throwable e) {
        v = handler.apply(e);
    }
    return v;
}

然后我不得不修改它以使它变得通用。这是生成try / catch部分的代码：

    int varOffset = context.getVarOffset();

    Label l0 = new Label();
    Label l1 = new Label();
    Label l2 = new Label();
    Label l3 = new Label();
    Label l4 = new Label();
    Label l5 = new Label();

    // mv.visitLocalVariable("v", "Ljava/lang/Object;", null, l1, l2, 2); // 2 == varOffset + 0
    context.push(1, new VarInfo(varOffset, "v1", l1, l2, false, "java/lang/Object"));
    // mv.visitLocalVariable("v", "Ljava/lang/Object;", null, l3, l5, 2); // 2 == varOffset + 0
    context.push(1, new VarInfo(varOffset, "v2", l3, l5, false, "java/lang/Object"));
    // mv.visitLocalVariable("e", "Ljava/lang/Throwable;", null, l4, l3, 3); // 3 == varOffset+1
    context.push(1, new VarInfo(varOffset + 1, "e", l4, l3, false, "java/lang/Throwable"));

    mv.visitTryCatchBlock(l0, l1, l2, "java/lang/Throwable");
    mv.visitLabel(l0);
    mv.visitLineNumber(50, l0);

    args[0].visit(context, mv); // mv.visitVarInsn(ALOAD, 0); // execute block
    mv.visitVarInsn(ASTORE, varOffset); // store v, the result

    mv.visitLabel(l1);
    mv.visitJumpInsn(GOTO, l3);
    mv.visitLabel(l2);
    mv.visitLineNumber(51, l2);
    // mv.visitFrame(Opcodes.F_SAME1, 0, null, 1, new Object[] { "java/lang/Throwable" });
    mv.visitVarInsn(ASTORE, varOffset + 1); // e
    mv.visitLabel(l4);
    mv.visitLineNumber(52, l4);

    args[1].visit(context, mv); // mv.visitVarInsn(ALOAD, 1); // catch block
    mv.visitVarInsn(ALOAD, varOffset + 1); // e

    mv.visitMethodInsn(INVOKEVIRTUAL, "com/pkg/lang/Lambda1", "apply", "(Ljava/lang/Object;)Ljava/lang/Object;");
    mv.visitVarInsn(ASTORE, varOffset); // store v, the result

    mv.visitLabel(l3);
    mv.visitLineNumber(54, l3);
    // mv.visitFrame(F_APPEND, 1, new Object[] { "java/lang/Object" }, 0, null);
    mv.visitVarInsn(ALOAD, varOffset); // load v, the result
    // mv.visitInsn(ARETURN);
    mv.visitLabel(l5);
    // mv.visitLocalVariable("test", "Ljava/lang/Object;", null, l0, l5, 0);
    // mv.visitLocalVariable("handler", "Lcom/pkg/lang/Lambda1;", null, l0, l5, 1);

Answer 1

我正在回答这个问题时假设你说：

// mv.visitLocalVariable("v", "Ljava/lang/Object;", null, l1, l2, 2); // 2 == varOffset + 0
context.push(1, new VarInfo(varOffset, "v1", l1, l2, false, "java/lang/Object"));

您的意思是context.push创建了mv.visitLocalVariable。

我认为必须先访问标签l1和l2，然后才能访问本地变量。

请参阅method visitor

的ASM4 java doc

在访问之前，必须在访问参数时调用之前调用之前调用的标签，并且在访问参数后传递的标签之后，必须调用visitLocalVariable和visitLineNumber方法。

不遵循上述规定可能会导致堆栈图生成错误。因此，在context.push之后将mv.visitLabel(l5)移动到底部应该使用正确的堆栈映射生成代码。

Answer 2

我在ASM列表上询问过，有人提供了这个提示：

“尝试使用带有checkDataFlow选项的CheckClassAdapter来获取更多详细信息。”

这有一些故障排除修复了问题。我很确定这与未正确区分绑定变量的范围以及需要使用visitLocalVariable声明本地变量有关。至少这是我在它不工作和开始工作之间修复的事情之一。

方法中的局部变量类型错误

2 个答案: