MSIL Hello World

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最近由于需要，开始阅读 MSIL 方面的东西。我读的是《.NET 探秘——MSIL 权威指南》（《Expert .NET 2.0 IL Assembler》中译版）。感觉没什么好说的，毕竟只要对 .NET 及其后面的东西了解一些，然后当做汇编来看，就好了。剩下的就是实践。

如书上所言，前面已经有人做出了这项研究了，如 Anders Liu、装配脑袋、Flier Lu。前辈们都是老手了，我也不好说什么，毕竟我刚刚入门。

这里就贴出昨晚写的一个 HelloWorld 程序吧。读了4天的收获。为了方便没学过 MSIL 的同志们，在上面都附上了实现同样功能的 C# 代码。

嗯，高级的东西还不敢说，要再仔细看，多练习才行啊。

.assembly extern mscorlib { auto }
.assembly MyIlApp { }
.module MyIlApp.exe

.namespace MyIlApp
{
    // public struct VC
    .class public value sealed auto VC
    {
        // public int val_int32;
        .field public int32 val_int32
        // public string val_string;
        .field public string val_string
    }

    // public sealed class MainClass
    .class public sealed auto ansi MainClass
    {

        // public static int _val;
        .field public static int32 _val

        // public static void check(int argument1)
        .method public static void check(int32) cil managed
        {
            // string temp;
            .locals init ([0]string temp)

            // if (MyIlApp.MainClass._val == argument1)
            // {
            //     System.Console.WriteLine("The value equals to the argument.");
            // }
            // else
            // {
            //     System.Console.WriteLine("The value does not equal to the argument.");
            // }
            ldsfld int32 MyIlApp.MainClass::_val
            ldarg.0
            beq TrueEqual
            ldstr "The value does not equal to the argument."
            call void [mscorlib]System.Console::WriteLine(string)
            br ThisIsEnd
            TrueEqual:
            ldstr "The value equals to the argument."
            call void [mscorlib]System.Console::WriteLine(string)

            // temp = argument1.ToString();    // 注意这里用 call 而不是 callvirt，因为 argument1 是 int32 类型，未装箱的时候没有V表
            ThisIsEnd:
            ldarga.s 0
            call instance string [mscorlib]System.Int32::ToString()
            stloc.0

            // System.Console.Write("The real value is:");
            ldstr "The real value is: "
            call void [mscorlib]System.Console::Write(string)

            // System.Console.WriteLine(temp);
            ldloc.0
            call void [mscorlib]System.Console::WriteLine(string)

            // return;
            ret
        }

        // public static void Main()
        .method public static void Main() cil managed
        {
            // .entrypoint 伪指令表示是程序入口点
            .entrypoint

            /* Test Case 1 */

            // string input;
            // int v;
            .locals init ([0] string input,
                          [1] int32 v)

            // System.Console.WriteLine("Hi. Please input a string:");
            ldstr "Hi. Please input a string:"
            call void [mscorlib]System.Console::WriteLine(string)

            // input = System.Console.ReadLine();
            call string [mscorlib]System.Console::ReadLine()
            stloc.0

            // System.Console.WriteLine(input);
            ldloc.0
            call void [mscorlib]System.Console::WriteLine(string)

            // v = System.Int32.Parse(input);
            ldloc.0
            call int32 [mscorlib]System.Int32::Parse(string)
            stloc.1

            // MyIlApp.MainClass._val = 9000;
            ldc.i4 9000
            stsfld int32 MyIlApp.MainClass::_val

            // System.Console.WriteLine(MyIlApp.MainClass._val.ToString());
            ldsflda int32 MyIlApp.MainClass::_val
            call instance string [mscorlib]System.Int32::ToString()
            call void [mscorlib]System.Console::WriteLine(string)

            // MyIlApp.MainClass.check(v);
            ldloc.1
            call void [MyIlApp]MyIlApp.MainClass::check(int32)

            /* Test Case 2 */


            // VC vc1;
            .locals init ([2] valuetype [MyIlApp]MyIlApp.VC vc1)

            // vc1.val_string = "Test string of VC";
            ldloca.s 2
            ldstr "Test string of VC"
            stfld string MyIlApp.VC::val_string

            // vc1.val_int32 = 8;
            ldloca.s 2
            ldc.i4.8
            stfld int32 MyIlApp.VC::val_int32

            // System.Console.WriteLine(vc1.val_string);
            ldloca.s 2
            ldfld string MyIlApp.VC::val_string
            call void [mscorlib]System.Console::WriteLine(string)

            // System.Console.WriteLine(vc1.val_int32.ToString());    // 《Expert .NET 2.0 IL Assembler》上说 ldflda “不能使用值类型的实例，也不能获取指向值类型实例的对象引用或指针”，有误。为了实现类似 a.X = 100（a 为 System.Drawing.Point 类型）这样的调用，需要用到 call 指令，也就需要用到 ldflda 而不是 ldfld；不过后者可以用在不访问实例函数/字段的情况下
            ldloca.s 2
            ldflda int32 MyIlApp.VC::val_int32
            call instance string [mscorlib]System.Int32::ToString()
            call void [mscorlib]System.Console::WriteLine(string)

            // return;
            ret
        }

    }
}