FastHook——巧妙利用动态代理实现非侵入式AOP

一、概述

FastHook框架要求调用者准备与原方法参数一致的Hook方法和Forward方法，这些限制将业务逻辑和Hook逻辑耦合在一起。若不了解FastHook原理，请移步FastHook——一种高效稳定、简洁易用的Android Hook框架
因此可能需要一种新实现方式，其可将业务逻辑和Hook逻辑解耦。一种简单的方案便是动态生成Hook方法和Forword方法。然而该方案对性能的影响比较大，动态生成dex文件并加载是耗时操作。
本文将介绍一种新的思路，统一Hook方法，利用动态代理创建Forward方法。该方案比上述方案更加高效、简洁。

二、Hook方法

Hook方法必须能实现以下两点需求
1. 能正确识别原方法
2. 能正确解析原方法参数

2.1 ART方法调用约定

以32位arm平台为例

    /*
     * Quick invocation stub internal.
     * On entry:
     *   r0 = method pointer
     *   r1 = argument array or null for no argument methods
     *   r2 = size of argument array in bytes
     *   r3 = (managed) thread pointer
     *   [sp] = JValue* result
     *   [sp + 4] = result_in_float
     *   [sp + 8] = core register argument array
     *   [sp + 12] = fp register argument array
     *  +-------------------------+
     *  | uint32_t* fp_reg_args   |
     *  | uint32_t* core_reg_args |
     *  |   result_in_float       | <- Caller frame
     *  |   Jvalue* result        |
     *  +-------------------------+
     *  |          lr             |
     *  |          r11            |
     *  |          r9             |
     *  |          r4             | <- r11
     *  +-------------------------+
     *  | uint32_t out[n-1]       |
     *  |    :      :             |        Outs
     *  | uint32_t out[0]         |
     *  | StackRef<ArtMethod>     | <- SP  value=null
     *  +-------------------------+
     */

1. r0寄存器存放被调用方法ArtMethod指针
2. r1~r3存放前3个参数
3. 从（sp+指针长度）地址起，按照参数顺序依次存放参数
显而易见，只需将被调用方法ArtMethod指针与sp指针传如Hook方法即可。32位指针长度为4字节，将以int类型传入，一种返回类型对应一个Hook方法。

private static Object hookHandleObject(int targetArtMethod, int sp) {
	FastHookParam param = hookHandle(targetArtMethod,sp);

	return param.result;
}

private static boolean hookHandleBoolean(int targetArtMethod, int sp) {
	FastHookParam param = hookHandle(targetArtMethod,sp);
	
	if(param.result != null && param.result instanceof Boolean) {
            return ((Boolean) param.result).booleanValue();
        }	

	return false;
}

private static byte hookHandleByte(int targetArtMethod, int sp) {
	FastHookParam param = hookHandle(targetArtMethod,sp);

	if(param.result != null && param.result instanceof Byte) {
            return ((Byte) param.result).byteValue();
        }
        
        return 0;
}

private static char hookHandleChar(int targetArtMethod, int sp) {
        FastHookParam param = hookHandle(targetArtMethod,sp);

	if(param.result != null && param.result instanceof Character) {
            return ((Character) param.result).charValue();
        }	

	return 0;
}

private static short hookHandleShort(int targetArtMethod, int sp) {
        FastHookParam param = hookHandle(targetArtMethod,sp);

	if(param.result != null && param.result instanceof Short) {
            return ((Short) param.result).shortValue();
        }	
        
	return 0;
}

private static int hookHandleInt(int targetArtMethod, int sp) {
        FastHookParam param = hookHandle(targetArtMethod,sp);
        
	if(param.result != null && param.result instanceof Integer) {
            return ((Integer) param.result).intValue();
        }

	return 0;
}

private static long hookHandleLong(int targetArtMethod, int sp) {
        FastHookParam param = hookHandle(targetArtMethod,sp);

	if(param.result != null && param.result instanceof Long) {
            return ((Long) param.result).longValue();
        }

	return 0;
}

private static float hookHandleFloat(int targe