C# PEファイルのMS-DOSヘッダとNTヘッダのシグネチャをメモリマップトファイルで読み込む

PEファイルのMS-DOSヘッダ（IMAGE_DOS_HEADER）とNTヘッダ（IMAGE_NT_HEADERS）のシグネチャをメモリマップトファイルで読み込むサンプルコードです。IMAGE_DOS_HEADERは固定長配列を含むため、マーシャリングとGCHandleを利用しています。IMAGE_NT_HEADERSは最初のフィールドがシグネチャなので直接読み込んでいます。

using System;
using System.IO;
using System.IO.MemoryMappedFiles;
using System.Runtime.InteropServices;
using System.Text;

class Program
{
    static void Main()
    {
        var path = Path.Combine(Environment.SystemDirectory, "notepad.exe");

        using var mmap = MemoryMappedFile.CreateFromFile(path, FileMode.Open, null, 0, MemoryMappedFileAccess.Read);
        using var accessor = mmap.CreateViewAccessor(0, 0, MemoryMappedFileAccess.Read);

        ReadMarshalStructure<IMAGE_DOS_HEADER>(accessor, 0, out var imgDosHdr);
        var mzSignature = imgDosHdr.e_magic; // 0x5a4d
        var peSignature = accessor.ReadUInt32(imgDosHdr.e_lfanew); // 0x00004550
        var mzSignatureStr = Encoding.ASCII.GetString(BitConverter.GetBytes(mzSignature)); // "MZ"
        var peSignatureStr = Encoding.ASCII.GetString(BitConverter.GetBytes(peSignature)); // "PE\0\0"
    }

    private static void ReadMarshalStructure<T>(MemoryMappedViewAccessor accessor, long position, out T obj)
        where T : struct
    {
        var buffer = new byte[Marshal.SizeOf<T>()];
        accessor.ReadArray<byte>(position, buffer, 0, buffer.Length);
        var handle = default(GCHandle);
        try
        {
            handle = GCHandle.Alloc(buffer, GCHandleType.Pinned);
            obj = Marshal.PtrToStructure<T>(handle.AddrOfPinnedObject());
        }
        finally
        {
            handle.Free();
        }
    }

    [StructLayout(LayoutKind.Sequential)]
    private struct IMAGE_DOS_HEADER
    {
        public ushort e_magic;
        public ushort e_cblp;
        public ushort e_cp;
        public ushort e_crlc;
        public ushort e_cparhdr;
        public ushort e_minalloc;
        public ushort e_maxalloc;
        public ushort e_ss;
        public ushort e_sp;
        public ushort e_csum;
        public ushort e_ip;
        public ushort e_cs;
        public ushort e_lfarlc;
        public ushort e_ovno;
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
        public ushort[] e_res;
        public ushort e_oemid;
        public ushort e_oeminfo;
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 10)]
        public ushort[] e_res2;
        public int e_lfanew;
    }
}