如何在 IL 中调用同一类中的方法

Question

如果我正在编写代码，这将非常简单。我的代码看起来像：

public class SomeClass
{
    public void SomeMethod(ISomeService someService)
    {
    }

    private void AnotherMethod(ISomeService someService)
    {
    }
}

我可以使用 Type 引用获取这两种方法的 Method 定义，但我想要获取的是从 SomeMethod 到在 IL 中添加的 AnotherMethod 的调用，因此您将拥有类似的等效代码：

public void SomeMethod(ISomeService someService)
{
    AnotherMethod(someService);
}

此刻我完全迷失了，试图理解如何正确构建必要的指令。

我现在的样子是这样的：

private void ProcessType(TypeDefinition typeDef)
{
    var anotherMethodDef = typeDef.Methods.FirstOrDefault(x => HasMethod(x, "AnotherMethod"));
    if(someMethodDef != null)
    {
        var someMethodDef = typeDef.Methods.First(x => HasMethod(x, "SomeMethod"));
        var processor = someMethodDef.Body.GetILProcessor();

        // Now I need to generate:
        // AnotherMethod(someService); as a new instruction
    }
}

private static bool HasMethod(MethodDefinition method, string expected) =>
    method.Name == expected && method.Parameters.Count() == 1 &&
        method.Parameters.First().TypeDefinition.FullName == "Contoso.ISomeService";

Answer 1

不确定这是否有帮助，但SomeMethod 的 IL：

    .maxstack 8

    IL_0000: nop
    IL_0001: ret

SomeMethod 和AnotherMethod(someService); 的 IL

    .maxstack 8

    IL_0000: nop
    IL_0001: ldarg.0
    IL_0002: ldarg.1
    IL_0003: call instance void SomeClass::AnotherMethod(class [YourAssembly]YourNamespace.ISomeService)
    IL_0008: nop
    IL_0009: ret

所以你想在中间添加这个：

    // Add breakpoint space (https://stackoverflow.com/questions/4590382/why-does-generated-il-code-start-with-a-nop)
    IL_0000: nop
    // Load `this` (https://stackoverflow.com/questions/1785372/why-do-i-have-to-do-ldarg-0-before-calling-a-field-in-msil)
    IL_0001: ldarg.0
    // Load your first argument... which is `someService`
    IL_0002: ldarg.1
    // Call method with this signature and previously loaded arguments
    IL_0003: call instance void SomeClass::AnotherMethod(class [YourAssembly]YourNamespace.ISomeService)

最后这应该可以解决问题：

var myAssembly = Assembly.GetAssembly(typeof(SomeClass));
var module = myAssembly.MainModule;
var anotherMethodRef = module.Import(typeof(SomeClass).GetMethod("AnotherMethod", new[] { typeof(ISomeService) }));

var nop = processor.Create(OpCodes.Nop);
var loadThis = processor.Create(OpCodes.Ldarg_0);
var loadSomeService = processor.Create(OpCodes.Ldarg_1);
var callMethod = processor.Create(OpCodes.Call, anotherMethodRef);

// First instruction was IL_0000: nop
var firstInstruction = someMethodDef.Body.Instructions[0];

processor.InsertBefore(firstInstruction, nop);
processor.InsertBefore(firstInstruction, loadThis);
processor.InsertBefore(firstInstruction, loadSomeService);
processor.InsertBefore(firstInstruction, callMethod);