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);
            }
        }
    }
}

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();

public void SayHello(bool print)
{
    if (print)
        Console.WriteLine("\tHello Cecil !");
}

TestType2 tt2 = new TestType2();
tt2.SayHello(true);
tt2.SayHello(false);
Console.ReadKey();

//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;

Mono.Cecil - 0.6

原文：http://www.cnblogs.com/lonelyxmas/p/5568866.html