C# 动态替换方法

public static void Run()
{
    //return 1
    var t1 = TestClass.Test1();
    //return 2
    var t2 = TestClass.Test2();
    var state = ReplaceMethod(typeof(TestClass).GetMethod("Test1"), typeof(TestClass).GetMethod("Test2"));
    //return 2 method is replaced!
    var t1Replace = TestClass.Test1();
    //return 2
    var t2Replace = TestClass.Test2();
}

public static unsafe MethodReplaceState ReplaceMethod(MethodInfo methodToReplace, MethodInfo methodToInject)
{
    RuntimeHelpers.PrepareMethod(methodToReplace.MethodHandle);
    RuntimeHelpers.PrepareMethod(methodToInject.MethodHandle);

    var tar = Calculation(methodToReplace);
    var inj = Calculation(methodToInject);

    tar = *(IntPtr*)tar + 1;
    inj = *(IntPtr*)inj + 1;
    MethodReplaceState state = new MethodReplaceState();
    state.Location = tar;
    state.OriginalLocation = new IntPtr(*(int*)tar);

    *(int*)tar = *(int*)inj + (int)(long)inj - (int)(long)tar;
    return state;
}

private static unsafe IntPtr Calculation(MethodInfo methodToReplace)
{
    IntPtr tar = methodToReplace.MethodHandle.Value;
    if (!methodToReplace.IsVirtual)
    {
        tar += 8;
    }
    else
    {
        var index = (int)(((*(long*)tar) >> 32) & 0xFF);
        var classStart = *(IntPtr*)(methodToReplace.DeclaringType.TypeHandle.Value + (IntPtr.Size == 4 ? 40 : 64));
        tar = classStart + IntPtr.Size + index;
    }
    return tar;
}

示例代码

ReplaceMethodTestDemo