🔀 PackedSwitchMethodItem

将 packed-switch-payload 指令渲染为 smali .packed-switch 块的专用类。

属性	值
完整类名	org.jf.baksmali.Adaptors.Format.PackedSwitchMethodItem
源码链接	Adaptors/Format/PackedSwitchMethodItem.java
继承	InstructionMethodItem<PackedSwitchPayload>

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🎯 职责

packed-switch 是 Dalvik 中针对连续整数 case（Java switch 语句的常见编译结果）的优化指令。PackedSwitchMethodItem 负责：

1. 通过 methodDef.getPackedSwitchBaseAddress(codeAddress) 反向查找宿主 packed-switch 指令的地址
2. 将每个 case 目标偏移转换为 LabelMethodItem（label 引用）或裸偏移（若基地址无效）
3. 输出完整的 .packed-switch firstKey ... .end packed-switch 多行块

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🧠 关键实现

构造函数：建立 case → label 映射

public PackedSwitchMethodItem(MethodDefinition methodDef, int codeAddress, PackedSwitchPayload instruction) {
    super(methodDef, codeAddress, instruction);

    int baseCodeAddress = methodDef.getPackedSwitchBaseAddress(codeAddress);

    targets = new ArrayList<PackedSwitchTarget>();
    boolean first = true;
    int firstKey = 0;
    if (baseCodeAddress >= 0) {
        for (SwitchElement switchElement: instruction.getSwitchElements()) {
            if (first) {
                firstKey = switchElement.getKey();
                first = false;
            }
            LabelMethodItem label = methodDef.getLabelCache().internLabel(
                    new LabelMethodItem(methodDef.classDef.options,
                            baseCodeAddress + switchElement.getOffset(), "pswitch_"));
            targets.add(new PackedSwitchLabelTarget(label));
        }
    } else {
        // 无法找到宿主指令时，退化为原始偏移输出
        for (SwitchElement switchElement: instruction.getSwitchElements()) {
            // ...
            targets.add(new PackedSwitchOffsetTarget(switchElement.getOffset()));
        }
    }
    this.firstKey = firstKey;
}

writeTo：多行输出

@Override
public boolean writeTo(IndentingWriter writer) throws IOException {
    writer.write(".packed-switch ");
    IntegerRenderer.writeTo(writer, firstKey);
    writer.indent(4);
    writer.write('\n');
    int key = firstKey;
    for (PackedSwitchTarget target: targets) {
        target.writeTargetTo(writer);
        writeResourceId(writer, key);  // 如果 key 是资源 ID，追加注释
        writer.write('\n');
        key++;
    }
    writer.deindent(4);
    writer.write(".end packed-switch");
    return true;
}

输出示例：

.packed-switch 0x1
    :pswitch_14
    :pswitch_1a
    :pswitch_22
.end packed-switch

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📌 小结

PackedSwitchMethodItem 展示了 payload 指令渲染的典型模式：构造时通过逆向映射（packedSwitchMap）找到宿主指令，从而将裸偏移转换为有意义的标签引用。内部使用策略模式（PackedSwitchLabelTarget vs PackedSwitchOffsetTarget）处理基地址有效/无效两种情况。

渲染流程与策略选择