ASM从堆栈帧中获取精确值

我有一些方法,其中包含像ILOAD这样的内容,我希望以某种方式在此指令之后获取堆栈的值.不只是打字,而是确切的价值.我知道我需要模拟方法执行才能做到这一点,但我不知道如何正确地做到这一点.
我有这样的测试方法叫main:

sipush          15649
istore_0        /* c */
getstatic       java/lang/System.out:Ljava/io/PrintStream;
bipush          45
bipush          11
iload_0         /* c */
...

我希望得到价值,加载iload_0.我试图制作分析器,然后看到帧值,但它们只包含值的类型,而不是我想要的.

ClassReader cr = new ClassReader(new FileInputStream(new File("input.class")));
ClassNode cn = new ClassNode(Opcodes.ASM5);
cr.accept(cn, 0);

Iterator methods = cn.methods.iterator();
while (methods.hasNext()) {
    MethodNode mn = methods.next();
    if (!mn.name.equals("main")) continue;
    AbstractInsnNode[] nodes = mn.instructions.toArray();
    Analyzer analyzer = new Analyzer(new BasicInterpreter());
    analyzer.analyze(cn.name, mn);
    int i = -1;
    for (Frame frame : analyzer.getFrames()) {
        i++;
        if (frame == null) continue;
        if (nodes[i].getOpcode() != Opcodes.ILOAD) continue;
        System.out.print(frame.getStack(0) + "|" + frame.getStack(1));
        System.out.print(" - " + nodes[i].getOpcode() + "\n");
    }
}

它显示了我的结果:R|I - 21 如何获得15649的价值？我试着谷歌那几个小时,找不到任何有用的东西.提前致谢.

您的代码几乎完全忽略了Java 5的优点.当你更新它,你会得到

for(MethodNode mn: cn.methods) {
    if(!mn.name.equals("main")) continue;
    Analyzer analyzer = new Analyzer<>(new BasicInterpreter());
    analyzer.analyze(cn.name, mn);
    int i = -1;
    for (Frame frame: analyzer.getFrames()) {
        i++;
        if(frame == null) continue;
        int opcode = mn.instructions.get(i).getOpcode();
        if(opcode != Opcodes.ILOAD) continue;
        BasicValue stackValue = frame.getStack(0);
        System.out.print(stackValue + "|" + frame.getStack(1));
        System.out.print(" - " + opcode + "\n");
    }
}

你可以立即看到你得到的是一个BasicValue,它适用于验证代码或计算stackmap帧,但不能获得实际值.

这是解释器的一个属性,BasicInterpreter只保留BasicValues(因此得名).另一种方法是SourceInterpreter允许您跟踪值可能来自哪些指令,这可能是istore_0您的情况,但这仍然没有给出实际值.

因此,如果您想获得实际值(如果可预测),则需要您自己的解释器.一个相当简单的,只有跟踪值才能真正源于推动常量:

import static org.objectweb.asm.Opcodes.*;
import java.util.List;
import java.util.Objects;
import org.objectweb.asm.Type;
import org.objectweb.asm.tree.*;
import org.objectweb.asm.tree.analysis.*;

public class ConstantTracker extends Interpreter {
    static final ConstantValue NULL = new ConstantValue(BasicValue.REFERENCE_VALUE, null);
    public static final class ConstantValue implements Value {
        final Object value; // null if unknown or NULL
        final BasicValue type;
        ConstantValue(BasicValue type, Object value) {
            this.value = value;
            this.type = Objects.requireNonNull(type);
        }
        @Override public int getSize() { return type.getSize(); }
        @Override public String toString() {
            Type t = type.getType();
            if(t == null) return "uninitialized";
            String typeName = type==BasicValue.REFERENCE_VALUE? "a reference type": t.getClassName();
            return this == NULL? "null":
                value == null? "unknown value of "+typeName: value+" ("+typeName+")";
        }
        @Override
        public boolean equals(Object obj) {
            if(this == obj) return true;
            if(this == NULL || obj == NULL || !(obj instanceof ConstantValue))
                return false;
            ConstantValue that = (ConstantValue)obj;
            return Objects.equals(this.value, that.value)
                && Objects.equals(this.type, that.type);
        }
        @Override
        public int hashCode() {
            if(this == NULL) return ~0;
            return (value==null? 7: value.hashCode())+type.hashCode()*31;
        }
    }

    BasicInterpreter basic = new BasicInterpreter() {
        @Override public BasicValue newValue(Type type) {
            return type!=null && (type.getSort()==Type.OBJECT || type.getSort()==Type.ARRAY)?
                   new BasicValue(type): super.newValue(type);
        }
        @Override public BasicValue merge(BasicValue a, BasicValue b) {
            if(a.equals(b)) return a;
            if(a.isReference() && b.isReference())
                // this is the place to consider the actual type hierarchy if you want
                return BasicValue.REFERENCE_VALUE;
            return BasicValue.UNINITIALIZED_VALUE;
        }
    };

    public ConstantTracker() {
        super(ASM5);
    }

    @Override
    public ConstantValue newOperation(AbstractInsnNode insn) throws AnalyzerException {
        switch(insn.getOpcode()) {
            case ACONST_NULL: return NULL;
            case ICONST_M1: case ICONST_0: case ICONST_1: case ICONST_2:
            case ICONST_3: case ICONST_4: case ICONST_5:
                return new ConstantValue(BasicValue.INT_VALUE, insn.getOpcode()-ICONST_0);
            case LCONST_0: case LCONST_1:
                return new ConstantValue(BasicValue.LONG_VALUE, (long)(insn.getOpcode()-LCONST_0));
            case FCONST_0: case FCONST_1: case FCONST_2:
                return new ConstantValue(BasicValue.FLOAT_VALUE, (float)(insn.getOpcode()-FCONST_0));
            case DCONST_0: case DCONST_1:
                return new ConstantValue(BasicValue.DOUBLE_VALUE, (double)(insn.getOpcode()-DCONST_0));
            case BIPUSH: case SIPUSH:
                return new ConstantValue(BasicValue.INT_VALUE, ((IntInsnNode)insn).operand);
            case LDC:
                return new ConstantValue(basic.newOperation(insn), ((LdcInsnNode)insn).cst);
            default:
                BasicValue v = basic.newOperation(insn);
                return v == null? null: new ConstantValue(v, null);
        }
    }

    @Override
    public ConstantValue copyOperation(AbstractInsnNode insn, ConstantValue value) {
        return value;
    }

    @Override
    public ConstantValue newValue(Type type) {
        BasicValue v = basic.newValue(type);
        return v == null? null: new ConstantValue(v, null);
    }

    @Override
    public ConstantValue unaryOperation(AbstractInsnNode insn, ConstantValue value) throws AnalyzerException {
        BasicValue v = basic.unaryOperation(insn, value.type);
        return v == null? null: new ConstantValue(v, insn.getOpcode()==CHECKCAST? value.value: null);
    }

    @Override
    public ConstantValue binaryOperation(AbstractInsnNode insn, ConstantValue a, ConstantValue b) throws AnalyzerException {
        BasicValue v = basic.binaryOperation(insn, a.type, b.type);
        return v == null? null: new ConstantValue(v, null);
    }

    @Override
    public ConstantValue ternaryOperation(AbstractInsnNode insn, ConstantValue a, ConstantValue b, ConstantValue c) {
        return null;
    }

    @Override
    public ConstantValue naryOperation(AbstractInsnNode insn, List values) throws AnalyzerException {
        List unusedByBasicInterpreter = null;
        BasicValue v = basic.naryOperation(insn, unusedByBasicInterpreter);
        return v == null? null: new ConstantValue(v, null);
    }

    @Override
    public void returnOperation(AbstractInsnNode insn, ConstantValue value, ConstantValue expected) {}

    @Override
    public ConstantValue merge(ConstantValue a, ConstantValue b) {
        if(a == b) return a;
        BasicValue t = basic.merge(a.type, b.type);
        return t.equals(a.type) && (a.value==null&&a!=NULL || a.value.equals(b.value))? a:
               t.equals(b.type) &&  b.value==null&&b!=NULL? b: new ConstantValue(t, null);
    }
}

那么,你可以像使用它一样

private static void analyze() throws IOException, AnalyzerException {
    ClassReader cr = new ClassReader(new FileInputStream(new File("input.class")));
    ClassNode cn = new ClassNode(Opcodes.ASM5);
    cr.accept(cn, 0);

    for(MethodNode mn: cn.methods) {
        if(!mn.name.equals("main")) continue;
        Analyzer analyzer
                = new Analyzer<>(new ConstantTracker());
        analyzer.analyze(cn.name, mn);
        int i = -1;
        for(Frame frame: analyzer.getFrames()) {
            i++;
            if(frame == null) continue;
            AbstractInsnNode n = mn.instructions.get(i);
            if(n.getOpcode() != Opcodes.ILOAD) continue;
            VarInsnNode vn = (VarInsnNode)n;
            System.out.println("accessing variable # "+vn.var);
            ConstantTracker.ConstantValue var = frame.getLocal(vn.var);
            System.out.println("\tcontains "+var);
        }
    }
}

^{这适用于所有负载指令不仅ILOAD,即ALOAD,LLOAD,FLOAD,和DLOAD}

当然,解释器还有很大的改进空间,比如用于跟踪int常量转换short或者byte简单数学的简单转换,但我认为现在图片更清晰,这取决于你的实际用例,你想跟踪多少或解释.