问题描述
public class Test
{
internal const string a = "some value";
private DateTime b = new DateTime();
}
如何使用 Mono Cecil 更改它们的初始值,使其看起来像这样:
public class Test
{
internal const string a = "test";
private DateTime b = DateTime.MaxValue;
}
void Main()
{
var input = @"C:\my_projects\a.exe";
var asm = AssemblyDeFinition.ReadAssembly(input);
foreach (ModuleDeFinition module in asm.Modules)
{
foreach (TypeDeFinition type in module.GetTypes())
{
foreach (var field in type.Fields)
{
if (field.Name == "a")
{
}
else if (field.Name == "b")
{
}
}
}
}
asm.Write(@"c:\my_projects\b.exe");
}
解决方法
免责声明
前面的代码非常脆弱
对于常量,它是设置 fld.Constant
属性的问题。
对于实例/静态字段,C# 编译器将在构造函数中发出初始化代码,因此您需要找到加载将存储在该字段中的值并替换它的指令。
using System.IO;
using System.Linq;
using Mono.Cecil;
using Mono.Cecil.Cil;
namespace x
{
class Program
{
public const string ConstValue = "old";
public int instanceField = 1;
static void Main(string[] args)
{
var o = new Program();
if (o.instanceField == 1)
{
using var a = AssemblyDefinition.ReadAssembly(typeof(Program).Assembly.Location);
var t = a.MainModule.Types.Single(ct => ct.Name == "Program");
var constant = t.Fields.First(f => f.Name == "ConstValue");
constant.Constant = "new value";
var ctor = t.Methods.Single(m => m.IsConstructor);
System.Console.WriteLine(ctor);
var il = ctor.Body.GetILProcessor();
var inst = il.Body.Instructions.First();
while (inst != null)
{
System.Console.WriteLine($"Checking {inst}");
if (inst.OpCode == OpCodes.Stfld && ((FieldReference) inst.Operand).Name == "instanceField")
{
// notice that this is very fragile. For this specific
// case I'd say it is safe but depending on how you
// initialize the field the instruction that loads
// the value to be assigned to the field may be located
// several instructions prior to the actual assignment
// but you can keep track of the stack state and figure
// out which instruction is pushing the value that
// will end up being poped into the field.
il.Replace(inst.Previous,il.Create(OpCodes.Ldc_I4,42));
System.Console.WriteLine("Found");
break;
}
inst = inst.Next;
}
var p = typeof(Program).Assembly.Location;
var newBinaryPath = Path.Combine(Path.GetDirectoryName(p),Path.GetFileNameWithoutExtension(p) + "2" +Path.GetExtension(p));
a.Write(newBinaryPath);
System.Console.WriteLine($"New binary writen to {newBinaryPath}");
}
System.Console.WriteLine(o.instanceField);
// Notice that no matter what you do,this will always print the
// old value; that happens because the C# compiler will emit the
// constant at the call site (instead of referencing the field
// at runtime)
System.Console.WriteLine(ConstValue);
}
}
}