将字节数组封送到C＃结构

Question

我正在研究用于读取FAT32引导扇区和BPB的C＃项目，问题是我正在使用编组机制将字节数组转换为自定义FAT32数据结构。 我收到一条消息错误说：无法从程序集“FAT32Management，Version = 1.0.0.0，Culture = neutral，PublicKeyToken = null”加载类型“FAT32Management.Fat32BootSector”，因为它包含偏移量为3的对象字段未正确对齐或重叠由非对象字段。

我无法解决问题

这是代码

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;

namespace FAT32Management
{
    [StructLayout(LayoutKind.Explicit)]//, CharSet = CharSet.Ansi, Size = 96, Pack = 1)]
    public struct Fat32BootSector
    {
        #region Common Region With all FAT systems
        /// <summary>
        /// First 3 Bytes of the Jump insctructions.
        /// Offset 0x00  
        /// </summary>
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 3)]
        [FieldOffset(0x00)]
        public byte[] JumpBootInstructions;

        /// <summary>
        /// 8 Bytes of the OemName
        /// Offset 0x03
        /// </summary>
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 8)]
        [FieldOffset(0x03)]
        public string OemName;

        #region BIOS Parameter Block (BPB)
        /// <summary>
        /// 2 Bytes of the BytesPerSector parameter. The BIOS Paramter Block Starts here
        /// Offset 0x0b  
        /// </summary>
        [MarshalAs(UnmanagedType.U2)]
        [FieldOffset(0x0b)]
        public ushort BpbBytesPerSector;

        /// <summary>
        /// 1 Byte containing the number of sectors per cluster. This must be a power of 2 from 1 to 128
        /// Offset 0x0d
        /// </summary>
        [MarshalAs(UnmanagedType.U1)]
        [FieldOffset(0x0d)]
        public byte BpbSectorsPerCluster;

        /// <summary>
        /// 2 Bytes for the Bpb reserved sectors count, Usually 32 for FAT32.
        /// Offset 0x0e  
        /// </summary>
        [MarshalAs(UnmanagedType.U2)]
        [FieldOffset(0x0e)]
        public ushort BpbReservedSectorsCount;

        /// <summary>
        /// 1 Byte Number of file allocation tables. Almost always 2.
        /// Offset 0x10
        /// </summary>
        [MarshalAs(UnmanagedType.U1)]
        [FieldOffset(0x10)]
        public byte BpbFatCount;

        /// <summary>
        /// 2 Bytes, Maximum number of root directory entries. Only used on FAT12 and FAT16
        /// Offset 0x11
        /// </summary>
        [MarshalAs(UnmanagedType.U2)]
        [FieldOffset(0x11)]
        public ushort BpbMaxRootDirectoriesCount;

        /// <summary>
        /// 2 Bytes, Total sectors (if zero, use 4 byte value at offset 0x20) used only for FAT12 AND FAT16 Systems
        /// Offset 0x13  
        /// </summary>
        [MarshalAs(UnmanagedType.U2)]
        [FieldOffset(0x13)]
        public ushort BpbTotalSectors16;

        /// <summary>
        /// 1 Byte, the media descriptor 
        /// Offset 0x15
        /// </summary>
        [MarshalAs(UnmanagedType.U1)]
        [FieldOffset(0x15)]
        public MediaDescriptor BpbMediaDescriptor;

        /// <summary>
        /// 2 Bytes, Sectors per File Allocation Table for FAT12/FAT16
        /// Offset 0x16
        /// </summary>
        [MarshalAs(UnmanagedType.U2)]
        [FieldOffset(0x16)]
        public ushort BpbSectorsPerFat16;

        /// <summary>
        /// 2 Bytes, Sectors per track
        /// Offset 0x18
        /// </summary>
        [MarshalAs(UnmanagedType.U2)]
        [FieldOffset(0x18)]
        public ushort BpbSectorsPerTrack;

        /// <summary>
        /// 2 Bytes Number of heads.
        /// Offset 0x1a
        /// </summary>
        [MarshalAs(UnmanagedType.U2)]
        [FieldOffset(0x1a)]
        public ushort BpbNumberOfHeads;

        /// <summary>
        /// 4 Bytes Hidden sectors.
        /// Offset 0x1c
        /// </summary>
        [MarshalAs(UnmanagedType.U4)]
        [FieldOffset(0x1c)]
        public uint BpbHiddenSectors;

        /// <summary>
        /// 4 Bytes, Total sectors (if greater than 65535; otherwise, see offset 0x13)
        /// Offset 0x20
        /// </summary>
        [MarshalAs(UnmanagedType.U4)]
        [FieldOffset(0x20)]
        public uint BpbTotalSectors32;

        #endregion

        #endregion

        #region Extended BIOS Parameter Block: FAT32 Specific 

        /// <summary>
        /// 4 Bytes for the number of sectors occupied by ONE FAT. 
        /// Offset 0x24
        /// </summary>
        [MarshalAs(UnmanagedType.U4)]
        [FieldOffset(0x24)]
        public uint FatSize32;

        /// <summary>
        /// 2 Bytes
        /// This field is only defined for FAT32 media and does not exist on FAT12 and FAT16 media.
        /// Bits 0-3 -- Zero-based number of active FAT. Only valid if mirroring is disabled.
        /// Bits 4-6 -- Reserved.
        /// Bit  7     -- 0 means the FAT is mirrored at runtime into all FATs.
        ///             -- 1 means only one FAT is active; it is the one referenced in bits 0-3.
        /// Bits 8-15  -- Reserved.
        /// Offset 0x28
        /// </summary>
        [MarshalAs(UnmanagedType.U2)]
        [FieldOffset(0x28)]
        public ushort ExtendedFlags;

        /// <summary>
        /// 2 Bytes for the file system version. The high byte is major revision number. Low byte is minor revision number. 
        /// Offset 0x2a
        /// </summary>
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 2)]
        [FieldOffset(0x24)]
        public byte[] FileSystemVersion;

        /// <summary>
        /// 4 Bytes for the first cluster number of the root directory
        /// Offset 0x2c
        /// </summary>
        [MarshalAs(UnmanagedType.U4)]
        [FieldOffset(0x2c)]
        public uint RootDirFirstClusterNumber;

        /// <summary>
        /// 2 Bytes for the Sector number of FS Information Sector.
        /// Offset 0x30
        /// </summary>
        [MarshalAs(UnmanagedType.U2)]
        [FieldOffset(0x30)]
        public ushort FSInfoSectorNumber;

        /// <summary>
        /// 2 Bytes. If non-zero, indicates the sector number in the reserved area of the volume of a copy of the boot record. Usually 6.
        /// Offset 0x32
        /// </summary>
        [MarshalAs(UnmanagedType.U2)]
        [FieldOffset(0x32)]
        public ushort BackupBootSectorNumber;

        /// <summary>
        /// 12 Reserved Bytes.
        /// Offset 0x34
        /// </summary>
        [MarshalAs(UnmanagedType.ByValArray,SizeConst = 12)]
        [FieldOffset(0x34)]
        public byte[] Reserved;

        /// <summary>
        /// 1 Byte for the physical drive number.
        /// Offset 0x40
        /// </summary>
        [MarshalAs(UnmanagedType.U1)]
        [FieldOffset(0x40)]
        public byte PhysicalDriveNumber;

        /// <summary>
        /// 1 Reserved byte.
        /// Offset 0x41
        /// </summary>
        [MarshalAs(UnmanagedType.U1)]
        [FieldOffset(0x41)]
        public byte Reserved1;

        /// <summary>
        /// 1 Byte. The boot signature
        /// Offset 0x42
        /// </summary>
        [MarshalAs(UnmanagedType.U1)]
        [FieldOffset(0x42)]
        public byte ExtendedBootSignature;

        /// <summary>
        /// 4 Bytes for the volume serial number.
        /// Offset 0x43
        /// </summary>
        [MarshalAs(UnmanagedType.U4)]
        [FieldOffset(0x43)]
        public uint VolumeID;

        /// <summary>
        /// 11 Byte for the volume label.
        /// Offset 0x47
        /// </summary>
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 11)]
        [FieldOffset(0x47)]
        public string VolumeLabel;

        /// <summary>
        /// 8 Bytes for the file system type string. 
        /// Offset 0x52
        /// </summary>
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 8)]
        [FieldOffset(0x52)]
        public string FileSystemType;

        #endregion

        /// <summary>
        /// Gets the boot sector for the specified drive.
        /// <remarks>The drive letter must have this pattern X: </remarks>
        /// </summary>
        /// <param name="driveLetter">The </param>
        /// <returns>The boot sector for the specified drive.</returns>
        public static Fat32BootSector GetBootSectorForDrive(string driveLetter)
        {
            byte[] bootSector = new byte[Marshal.SizeOf(typeof(Fat32BootSector))];
            string drive = @"\\.\" + driveLetter;
            IntPtr hardDiskPointer = SystemIOCalls.OpenFile(drive);
            // Seeks to the start of the partition
            SystemIOCalls.SeekAbsolute(hardDiskPointer, 0, 0);
            // Read the first reserved sector of the drive data (Boot Sector)
            // The data should be read with a chunk of 512 X byte.
            SystemIOCalls.ReadBytes(hardDiskPointer, bootSector, 512);
            SystemIOCalls.CloseHandle(hardDiskPointer);

            // Marshaling the bytes array to a valid struct
            GCHandle pinnedInfos = GCHandle.Alloc(bootSector, GCHandleType.Pinned);
            var infos = (Fat32BootSector)Marshal.PtrToStructure(pinnedInfos.AddrOfPinnedObject(), typeof(Fat32BootSector));
            pinnedInfos.Free();
            return infos;
        }
    }
}

请帮忙！

Answer 1

显式结构布局和FieldOffsetAttribute适用于编组，还适用于CLR使用的运行时布局。 如果在不安全的代码中使用struct类型定义，或者根据重叠数据做出其他假设（即有效地创建C风格的union类型），这一点尤为重要。

作为混淆显式字段布局的这两种用法的副作用，将禁止违反CLR类型系统的布局：重叠对象引用可以允许在运行过程中构造对任意数据的对象引用，而未对齐的对象引用会影响该类型GC实现可以使用的优化。

我相信你需要回归使用固定字节数组作为字符串数据，并使用Encoding类自行解码。 例如：

[FieldOffset(0x03)]
public fixed byte OemName[8]

fixed字段需要不安全的上下文，并且需要一次复制一个元素，或者在不安全的代码中作为例如byte*处理。

另一种方法是使用手动内存分配（ Marhsal.AllocHGlobal或byte[] ）并将数据视为blob，可能使用BinaryReader读取。

Answer 2

谢谢barry，我刚刚修改了它正在运行的代码

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;

namespace FAT32Management
{
    [StructLayout(LayoutKind.Explicit, CharSet = CharSet.Ansi, Size = 96, Pack = 1)]
    public unsafe struct Fat32BootSector
    {
        #region Common Region With all FAT systems
        /// <summary>
        /// First 3 Bytes of the Jump insctructions.
        /// Offset 0x00     
        /// </summary>
        //[MarshalAs(UnmanagedType.ByValArray, SizeConst = 3)]
        [FieldOffset(0x00)]
        public fixed byte JumpBootInstructions[3];

        /// <summary>
        /// 8 Bytes of the OemName
        /// Offset 0x03
        /// </summary>
        [FieldOffset(0x03)]
        public fixed char OemName[8];

        #region BIOS Parameter Block (BPB)
        /// <summary>
        /// 2 Bytes of the BytesPerSector parameter. The BIOS Paramter Block Starts here
        /// Offset 0x0b     
        /// </summary>
        [MarshalAs(UnmanagedType.U2)]
        [FieldOffset(0x0b)]
        public ushort BpbBytesPerSector;

        /// <summary>
        /// 1 Byte containing the number of sectors per cluster. This must be a power of 2 from 1 to 128
        /// Offset 0x0d
        /// </summary>
        [MarshalAs(UnmanagedType.U1)]
        [FieldOffset(0x0d)]
        public byte BpbSectorsPerCluster;

        /// <summary>
        /// 2 Bytes for the Bpb reserved sectors count, Usually 32 for FAT32.
        /// Offset 0x0e     
        /// </summary>
        [MarshalAs(UnmanagedType.U2)]
        [FieldOffset(0x0e)]
        public ushort BpbReservedSectorsCount;

        /// <summary>
        /// 1 Byte Number of file allocation tables. Almost always 2.
        /// Offset 0x10
        /// </summary>
        [MarshalAs(UnmanagedType.U1)]
        [FieldOffset(0x10)]
        public byte BpbFatCount;

        /// <summary>
        /// 2 Bytes, Maximum number of root directory entries. Only used on FAT12 and FAT16
        /// Offset 0x11
        /// </summary>
        [MarshalAs(UnmanagedType.U2)]
        [FieldOffset(0x11)]
        public ushort BpbMaxRootDirectoriesCount;

        /// <summary>
        /// 2 Bytes, Total sectors (if zero, use 4 byte value at offset 0x20) used only for FAT12 AND FAT16 Systems
        /// Offset 0x13     
        /// </summary>
        [MarshalAs(UnmanagedType.U2)]
        [FieldOffset(0x13)]
        public ushort BpbTotalSectors16;

        /// <summary>
        /// 1 Byte, the media descriptor 
        /// Offset 0x15
        /// </summary>
        [MarshalAs(UnmanagedType.U1)]
        [FieldOffset(0x15)]
        public MediaDescriptor BpbMediaDescriptor;

        /// <summary>
        /// 2 Bytes, Sectors per File Allocation Table for FAT12/FAT16
        /// Offset 0x16
        /// </summary>
        [MarshalAs(UnmanagedType.U2)]
        [FieldOffset(0x16)]
        public ushort BpbSectorsPerFat16;

        /// <summary>
        /// 2 Bytes, Sectors per track
        /// Offset 0x18
        /// </summary>
        [MarshalAs(UnmanagedType.U2)]
        [FieldOffset(0x18)]
        public ushort BpbSectorsPerTrack;

        /// <summary>
        /// 2 Bytes Number of heads.
        /// Offset 0x1a
        /// </summary>
        [MarshalAs(UnmanagedType.U2)]
        [FieldOffset(0x1a)]
        public ushort BpbNumberOfHeads;

        /// <summary>
        /// 4 Bytes Hidden sectors.
        /// Offset 0x1c
        /// </summary>
        [MarshalAs(UnmanagedType.U4)]
        [FieldOffset(0x1c)]
        public uint BpbHiddenSectors;

        /// <summary>
        /// 4 Bytes, Total sectors (if greater than 65535; otherwise, see offset 0x13)
        /// Offset 0x20
        /// </summary>
        [MarshalAs(UnmanagedType.U4)]
        [FieldOffset(0x20)]
        public uint BpbTotalSectors32;

        #endregion

        #endregion

        #region Extended BIOS Parameter Block: FAT32 Specific

        /// <summary>
        /// 4 Bytes for the number of sectors occupied by ONE FAT. 
        /// Offset 0x24
        /// </summary>
        [MarshalAs(UnmanagedType.U4)]
        [FieldOffset(0x24)]
        public uint FatSize32;

        /// <summary>
        /// 2 Bytes
        /// This field is only defined for FAT32 media and does not exist on FAT12 and FAT16 media.
        /// Bits 0-3    -- Zero-based number of active FAT. Only valid if mirroring is disabled.
        /// Bits 4-6    -- Reserved.
        /// Bit  7      -- 0 means the FAT is mirrored at runtime into all FATs.
        ///             -- 1 means only one FAT is active; it is the one referenced in bits 0-3.
        /// Bits 8-15   -- Reserved.
        /// Offset 0x28
        /// </summary>
        [MarshalAs(UnmanagedType.U2)]
        [FieldOffset(0x28)]
        public ushort ExtendedFlags;

        /// <summary>
        /// 2 Bytes for the file system version. The high byte is major revision number. Low byte is minor revision number. 
        /// Offset 0x2a
        /// </summary>
        [FieldOffset(0x2a)]
        public fixed byte FileSystemVersion[2];

        /// <summary>
        /// 4 Bytes for the first cluster number of the root directory
        /// Offset 0x2c
        /// </summary>
        [MarshalAs(UnmanagedType.U4)]
        [FieldOffset(0x2c)]
        public uint RootDirFirstClusterNumber;

        /// <summary>
        /// 2 Bytes for the Sector number of FS Information Sector.
        /// Offset 0x30
        /// </summary>
        [MarshalAs(UnmanagedType.U2)]
        [FieldOffset(0x30)]
        public ushort FSInfoSectorNumber;

        /// <summary>
        /// 2 Bytes. If non-zero, indicates the sector number in the reserved area of the volume of a copy of the boot record. Usually 6.
        /// Offset 0x32
        /// </summary>
        [MarshalAs(UnmanagedType.U2)]
        [FieldOffset(0x32)]
        public ushort BackupBootSectorNumber;

        /// <summary>
        /// 12 Reserved Bytes.
        /// Offset 0x34
        /// </summary>
        [FieldOffset(0x34)]
        public fixed byte Reserved[12];

        /// <summary>
        /// 1 Byte for the physical drive number.
        /// Offset 0x40
        /// </summary>
        [MarshalAs(UnmanagedType.U1)]
        [FieldOffset(0x40)]
        public byte PhysicalDriveNumber;

        /// <summary>
        /// 1 Reserved byte.
        /// Offset 0x41
        /// </summary>
        [MarshalAs(UnmanagedType.U1)]
        [FieldOffset(0x41)]
        public byte Reserved1;

        /// <summary>
        /// 1 Byte. The boot signature
        /// Offset 0x42
        /// </summary>
        [MarshalAs(UnmanagedType.U1)]
        [FieldOffset(0x42)]
        public byte ExtendedBootSignature;

        /// <summary>
        /// 4 Bytes for the volume serial number.
        /// Offset 0x43
        /// </summary>
        [MarshalAs(UnmanagedType.U4)]
        [FieldOffset(0x43)]
        public uint VolumeID;

        /// <summary>
        /// 11 Byte for the volume label.
        /// Offset 0x47
        /// </summary>
        [FieldOffset(0x47)]
        public fixed char VolumeLabel[11];

        /// <summary>
        /// 8 Bytes for the file system type string. 
        /// Offset 0x52
        /// </summary>
        [FieldOffset(0x52)]
        public fixed char FileSystemType[8];

        #endregion

        /// <summary>
        /// Gets the boot sector for the specified drive.
        /// <remarks>The drive letter must have this pattern X: </remarks>
        /// </summary>
        /// <param name="driveLetter">The </param>
        /// <returns>The boot sector for the specified drive.</returns>
        public static Fat32BootSector GetBootSectorForDrive(string driveLetter)
        {
            byte[] bootSector = new byte[Marshal.SizeOf(typeof(Fat32BootSector))];
            string drive = @"\\.\" + driveLetter;
            IntPtr hardDiskPointer = SystemIOCalls.OpenFile(drive);
            // Seeks to the start of the partition
            SystemIOCalls.SeekAbsolute(hardDiskPointer, 0, 0);
            // Read the first reserved sector of the drive data (Boot Sector)
            // The data should be read with a chunk of 512 X byte.
            SystemIOCalls.ReadBytes(hardDiskPointer, bootSector, 512);
            SystemIOCalls.CloseHandle(hardDiskPointer);

            // Marshaling the bytes array to a valid struct
            GCHandle pinnedInfos = GCHandle.Alloc(bootSector, GCHandleType.Pinned);
            var infos = (Fat32BootSector)Marshal.PtrToStructure(pinnedInfos.AddrOfPinnedObject(), typeof(Fat32BootSector));
            pinnedInfos.Free();
            return infos;
        }
    }
}