How to find if a native DLL file is compiled as x64 or x86?

I want to determine if a native assembly is complied as x64 or x86 from a managed code application (C#).

I think it must be somewhere in the PE header since the OS loader needs to know this information, but I couldn't find it. Of course I prefer to do it in managed code, but if it necessary, I can use native C++.

You can use DUMPBIN too. Use the /headers or /all flag and its the first file header listed.

dumpbin /headers cv210.dll

64-bit

Microsoft (R) COFF/PE Dumper Version 10.00.30319.01
Copyright (C) Microsoft Corporation.  All rights reserved.


Dump of file cv210.dll

PE signature found

File Type: DLL

FILE HEADER VALUES
            8664 machine (x64)
               6 number of sections
        4BBAB813 time date stamp Tue Apr 06 12:26:59 2010
               0 file pointer to symbol table
               0 number of symbols
              F0 size of optional header
            2022 characteristics
                   Executable
                   Application can handle large (>2GB) addresses
                   DLL

32-bit

Microsoft (R) COFF/PE Dumper Version 10.00.30319.01
Copyright (C) Microsoft Corporation.  All rights reserved.


Dump of file acrdlg.dll

PE signature found

File Type: DLL

FILE HEADER VALUES
             14C machine (x86)
               5 number of sections
        467AFDD2 time date stamp Fri Jun 22 06:38:10 2007
               0 file pointer to symbol table
               0 number of symbols
              E0 size of optional header
            2306 characteristics
                   Executable
                   Line numbers stripped
                   32 bit word machine
                   Debug information stripped
                   DLL

'find' can make life slightly easier:

dumpbin /headers cv210.dll |find "machine"
        8664 machine (x64)

There is an easy way to do this with CorFlags. Open the Visual Studio Command Prompt and type "corflags [your assembly]". You'll get something like this:

c:\Program Files (x86)\Microsoft Visual Studio 9.0\VC>corflags "C:\Windows\Microsoft.NET\Framework\v2.0.50727\System.Data.dll"

Microsoft (R) .NET Framework CorFlags Conversion Tool. Version 3.5.21022.8 Copyright (c) Microsoft Corporation. All rights reserved.

Version : v2.0.50727 CLR Header: 2.5 PE : PE32 CorFlags : 24 ILONLY : 0 32BIT : 0 Signed : 1

You're looking at PE and 32BIT specifically.

• Any CPU:

  PE: PE32
  32BIT: 0

• x86:

  PE: PE32
  32BIT: 1

• x64:

  PE: PE32+
  32BIT: 0