Check if unmanaged DLL is 32-bit or 64-bit?

Question

How can I programmatically tell in C# if an unmanaged DLL file is x86 or x64?

Answer 1

Refer to the specifications. Here's a basic implementation:

public static MachineType GetDllMachineType(string dllPath)
{
    // See http://www.microsoft.com/whdc/system/platform/firmware/PECOFF.mspx
    // Offset to PE header is always at 0x3C.
    // The PE header starts with "PE\0\0" =  0x50 0x45 0x00 0x00,
    // followed by a 2-byte machine type field (see the document above for the enum).
    //
    FileStream fs = new FileStream(dllPath, FileMode.Open, FileAccess.Read);
    BinaryReader br = new BinaryReader(fs);
    fs.Seek(0x3c, SeekOrigin.Begin);
    Int32 peOffset = br.ReadInt32();
    fs.Seek(peOffset, SeekOrigin.Begin);
    UInt32 peHead = br.ReadUInt32();

    if (peHead!=0x00004550) // "PE\0\0", little-endian
        throw new Exception("Can't find PE header");

    MachineType machineType = (MachineType) br.ReadUInt16();
    br.Close();
    fs.Close();
    return machineType;
}

The MachineType enum is defined as:

public enum MachineType : ushort
{
    IMAGE_FILE_MACHINE_UNKNOWN = 0x0,
    IMAGE_FILE_MACHINE_AM33 = 0x1d3,
    IMAGE_FILE_MACHINE_AMD64 = 0x8664,
    IMAGE_FILE_MACHINE_ARM = 0x1c0,
    IMAGE_FILE_MACHINE_EBC = 0xebc,
    IMAGE_FILE_MACHINE_I386 = 0x14c,
    IMAGE_FILE_MACHINE_IA64 = 0x200,
    IMAGE_FILE_MACHINE_M32R = 0x9041,
    IMAGE_FILE_MACHINE_MIPS16 = 0x266,
    IMAGE_FILE_MACHINE_MIPSFPU = 0x366,
    IMAGE_FILE_MACHINE_MIPSFPU16 = 0x466,
    IMAGE_FILE_MACHINE_POWERPC = 0x1f0,
    IMAGE_FILE_MACHINE_POWERPCFP = 0x1f1,
    IMAGE_FILE_MACHINE_R4000 = 0x166,
    IMAGE_FILE_MACHINE_SH3 = 0x1a2,
    IMAGE_FILE_MACHINE_SH3DSP = 0x1a3,
    IMAGE_FILE_MACHINE_SH4 = 0x1a6,
    IMAGE_FILE_MACHINE_SH5 = 0x1a8,
    IMAGE_FILE_MACHINE_THUMB = 0x1c2,
    IMAGE_FILE_MACHINE_WCEMIPSV2 = 0x169,
}

I only needed three of these, but I included them all for completeness. Final 64-bit check:

// Returns true if the dll is 64-bit, false if 32-bit, and null if unknown
public static bool? UnmanagedDllIs64Bit(string dllPath)
{
    switch (GetDllMachineType(dllPath))
    {
        case MachineType.IMAGE_FILE_MACHINE_AMD64:
        case MachineType.IMAGE_FILE_MACHINE_IA64:
            return true;
        case MachineType.IMAGE_FILE_MACHINE_I386:
            return false;
        default:
            return null;
    }
}