How to determine if a .NET assembly was built for x86 or x64?

Question

I've got an arbitrary list of .NET assemblies.

I need to programmatically check if each DLL was built for x86. (As opposed to x64 or Any CPU.) Is this possible?

Answer 1

You can use corflags CLI tool to determine the status of an assembly, based on its output and opening an assembly as a binary asset you should be able to determine where you need to seek to to determine if the 32BIT flag is set to 1 (x86) or 0 (any CPU).

Here's some information about corflags.

Update: even better, you can use Module.GetPEKind to determine whether an assembly is PortableExecutableKinds value PE32Plus (64-bit), Required32Bit (32-bit and WOW), or ILOnly (any CPU) along with other attributes.

Answer 2

Look at System.Reflection.AssemblyName.GetAssemblyName(string assemblyFile)

You can examine assembly metadata from the returned AssemblyName instance:

[36] > [reflection.assemblyname]::GetAssemblyName(".\Microsoft.GLEE.dll") | fl

Name                  : Microsoft.GLEE
Version               : 1.0.0.0
CultureInfo           :
CodeBase              : file:///C:/projects/powershell/BuildAnalyzer/Microsoft.GLEE.dll
EscapedCodeBase       : file:///C:/projects/powershell/BuildAnalyzer/Microsoft.GLEE.dll
**ProcessorArchitecture : MSIL**
Flags                 : PublicKey
HashAlgorithm         : SHA1
VersionCompatibility  : SameMachine
KeyPair               :
FullName              : Microsoft.GLEE, Version=1.0.0.0, Culture=neutral, PublicKeyToken=7f84f738e1fc245c

I'm using PowerShell in this example to call the method.

Answer 3

Just for clarification, CorFlags.exe is part of the .NET Framework SDK. I have the development tools on my machine, and the simplest way for me determine whether a DLL is 32-bit only is to:

1. Open the Visual Studio Command Prompt (In Windows: menu Start/Programs/Microsoft Visual Studio/Visual Studio Tools/Visual Studio 2008 Command Prompt)

2. CD to the directory containing the DLL in question

3. Run corflags like this: corflags MyAssembly.dll

You will get output something like this:

    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  : 3
ILONLY    : 1
32BIT     : 1
Signed    : 0

The key is the "32BIT" flag as documented above: 1 = x86; 0 = Any CPU.