Richie

Sometimes at night when I look up at the stars, and see the whole sky just laid out there, don't you think I ain't remembering it all. I still got dreams like anybody else, and ever so often, I am thinking about how things might of been. And then, all of a sudden, I'm forty, fifty, sixty years old, you know?

Mono.Cecil - 0.6

项目地址:Mono.Cecil
项目描述:In simple English, with Cecil, you can load existing managed assemblies, browse all the contained types, modify them on the fly and save back to the disk the modified assembly.
类似项目:Microsoft CCI
Common Compiler Infrastructure: Metadata API
Common Compiler Infrastructure: Code Model and AST API
Common Compiler Infrastructure: Sample applications
Common Compiler Infrastructure - Contrib
对比评价:来自StackOverflow
Mono.Cecil has better, more understandable and easy in use object model. However, I had an ugly bug when used it in my program (reference to the wrong method was saved in the assembly; I think there was some bug with metadata tokens handling)
Microsoft.CCI has an ugly, utterly over-designed object model in the same time lacking many simple features; however, it's more mature than Mono.Cecil. Finally, I abandoned Mono.Cecil and used Microsoft.CCI for my program.

基本示例
Cecil是对已编译生成IL的程序集进行操作,所以先写一个简单的Console exe程序,这里项目名称使用Cecil.Program:
using System;
using System.Reflection;
namespace Cecil.Program
{
    class Program
    {
        static void Main(string[] args)
        {
            TestType tt = new TestType();
            tt.SayHello();
            tt.AboutMe();
            Console.ReadKey();
        }
    }
    public class TestType
    {
        [Obsolete]
        public void SayHello()
        {
            Console.WriteLine("\tHello Cecil !");
        }
        public void AboutMe()
        {
            Type type = typeof(TestType);
            MethodInfo method = type.GetMethod("SayHello");
            if (method.IsVirtual)
                Console.WriteLine("\tI'm a virtual method");
            else
                Console.WriteLine("\tI'm a non-virtual method");
            object[] attributes = method.GetCustomAttributes(false);
            if (attributes != null && attributes.Length > 0)
            {
                Console.WriteLine("\tI have the following attributes:");
                foreach (object attr in attributes)
                    Console.WriteLine("\t\t" + attr.GetType().Name);
            }
        }
    }
}
这个程序集的运行结果如下:
    

方法SayHello的IL代码如下:
    

接下来使用另外一个Console exe程序来修改Cecil.Program.exe,项目名称使用Cecil:
using Mono.Cecil;
using Mono.Cecil.Cil;
AssemblyDefinition assembly = AssemblyFactory.GetAssembly("Cecil.Program.exe");
TypeDefinition type = assembly.MainModule.Types["Cecil.Program.TestType"];
MethodDefinition sayHello = null;
foreach (MethodDefinition md in type.Methods)
    if (md.Name == "SayHello") sayHello = md;
//Console.WriteLine(string value)方法
MethodInfo writeLine = typeof(Console).GetMethod("WriteLine"
    , new Type[] { typeof(string) });
//Console.WriteLine方法导入MainModule,并返回在AssemblyDefinition中的引用方式
MethodReference writeLineRef = assembly.MainModule.Import(writeLine);
//在SayHello方法开始位置插入一条trace语句
//  Console.WriteLine(">>Intercepting ");
//如果插入的语句需要使用函数入参,则必须插入在OpCodes.Ldarg等指令之后
CilWorker worker = sayHello.Body.CilWorker;
Instruction ldstr = worker.Create(OpCodes.Ldstr, ">>Intercepting " + sayHello.Name);
Instruction call = worker.Create(OpCodes.Call, writeLineRef);
Instruction first = sayHello.Body.Instructions[0];
worker.InsertBefore(first, call);
worker.InsertBefore(call, ldstr);
//在SayHello方法结束位置插入一条trace语句
//  Console.WriteLine(">>Intercepted ");
//语句必须插入在OpCodes.Ret指令的前面
int offset = sayHello.Body.Instructions.Count - 1;
Instruction last = sayHello.Body.Instructions[offset--];
while (last.OpCode == OpCodes.Nop || last.OpCode == OpCodes.Ret)
    last = sayHello.Body.Instructions[offset--];
ldstr = worker.Create(OpCodes.Ldstr, ">>Intercepted " + sayHello.Name);
worker.InsertAfter(last, ldstr);
worker.InsertAfter(ldstr, call);
//把SayHello方法改为虚方法
sayHello.IsVirtual = true;
//给SayHello方法添加一个SerializableAttribute
CustomAttribute attribute = new CustomAttribute(
    assembly.MainModule.Import(
        typeof(SerializableAttribute).GetConstructor(Type.EmptyTypes)
));
sayHello.CustomAttributes.Add(attribute);
AssemblyFactory.SaveAssembly(assembly, "Cecil.Program.modified.exe");
Console.WriteLine("Assembly modified successfully!");
Console.ReadKey();
编译生成Cecil.exe,然后把Cecil.Program.exe拷贝到这个目录下,运行Cecil.exe,便会在当前目录生成Cecil.Program.modified.exe,运行Cecil.Program.modified.exe结果如下:
    
修改后的方法SayHello的IL代码如下:
    

从上面的基本使用方法可以看出,Cecil的确是易于使用,对象模型结构非常实用,这里是官方网站的一个主要对象结构图:
    

IL指令的复杂性
在assembly、type、method级别上对程序集做修改是非常简单的,但是如果要修改方法体的IL代码,则可能会遇到一些较麻烦的事情,需要细致的处理
例如上面的SayHello方法如果是这样:
public void SayHello(bool print)
{
    if (print)
        Console.WriteLine("\tHello Cecil !");
}
测试代码这样来调用:
TestType2 tt2 = new TestType2();
tt2.SayHello(true);
tt2.SayHello(false);
Console.ReadKey();
其运行结果只会输出一条Hello Cecil !消息,仍然使用Cecil.exe来修改这个程序集,其运行结果如下图:
    
调用tt2.SayHello(false);时,应该也会有一个>>Intercepted SayHello消息,但是没有输出,对比一下IL代码就清楚了:
    
修改后的IL代码如下:
    
IL_000b那一句,为false时就直接跳转到IL_0021这个返回指令上了,不会输出Intercepted的消息

使用Mono.Cecil也可以修改这个跳转地址,例如:
//得到指令brfalse.s
Instruction jmp = sayHello.Body.Instructions[1];
....
//把跳转的目标地址改成IL_0017 ldstr指令位置
jmp.Operand = ldstr;

posted on 2010-03-21 00:02 riccc 阅读(...) 评论(...) 编辑 收藏

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