How to Tell if a .NET Assembly Was Compiled as x86, x64 or Any CPU

Question

What's the easiest way to discover (without access to the source project) whether a .NET assembly DLL was compiled as 'x86', 'x64' or 'Any CPU'?

Update: A command-line utility was sufficient to meet my immediate needs, but just for the sake of completeness, if someone wants to tell me how to do it programmatically then that would be of interest too, I'm sure.

Answer 1

If you just want to find this out on a given dll, then you can use the CorFlags tool that is part of the Windows SDK:

CorFlags.exe assembly.dll

---

If you want to do it using code, take a look at the GetPEKind method of the Module class:

Assembly assembly = Assembly.LoadFrom("path to dll");
PortableExecutableKinds peKind;
ImageFileMachine imageFileMachine;
assembly.ManifestModule.GetPEKind(out peKind, out imageFileMachine)

You then need to examine the peKind to check its value. See the MSDN docs for PortableExecutableKinds for more info.

Answer 2

Thanks Adrian! I've rewritten the snippet in PowerShell so I could use it on the server.

#USAGE #1
# Get-Bitness (dir *.dll | select -first 1)
#USAGE #2
# Get-Bitness "C:\vs\projects\bestprojectever\bin\debug\mysweetproj.dll"
function Get-Bitness([System.IO.FileInfo]$assemblyFile)
{
    $peKinds = new-object Reflection.PortableExecutableKinds
    $imageFileMachine = new-object Reflection.ImageFileMachine
    $a = [Reflection.Assembly]::LoadFile($assemblyFile.Fullname)
    $a.ManifestModule.GetPEKind([ref]$peKinds, [ref]$imageFileMachine)

    return $peKinds
}

Answer 3

Thanks Adrian and Peter! Here's a modified version of Peter's Get-Bitness that 1) takes a list of files to examine from the pipeline, and 2) doesn't die it if looks at a non-.NET DLL (e.g. if it looks at certain C++ DLLs):

# example usage: dir *.exe,*.dll | Get-PEKind
function Get-PEKind {
    Param(
      [Parameter(Mandatory=$True,ValueFromPipeline=$True)]
      [System.IO.FileInfo]$assemblies
    )

    Process {
        foreach ($assembly in $assemblies) {
            $peKinds = new-object Reflection.PortableExecutableKinds
            $imageFileMachine = new-object Reflection.ImageFileMachine
            try
            {
                $a = [Reflection.Assembly]::LoadFile($assembly.Fullname)
                $a.ManifestModule.GetPEKind([ref]$peKinds, [ref]$imageFileMachine)
            }
            catch [System.BadImageFormatException]
            {
                $peKinds = [System.Reflection.PortableExecutableKinds]"NotAPortableExecutableImage"
            }

            $o = New-Object System.Object
            $o | Add-Member -type NoteProperty -name File -value $assembly
            $o | Add-Member -type NoteProperty -name PEKind -value $peKinds
            Write-Output $o
        }
    }
}

I'm new to PowerShell, so this may not be an example of best practices.

Alternatively, according to https://stackoverflow.com/a/4719567/64257 there may also be a handy Get-PEHeader cmdlet in the PowerShell Community Extensions.

Answer 4

C# snippet, based on the Powershell answers:

var modules = assembly.GetModules();
var kinds = new List<PortableExecutableKinds>();
var images = new List<ImageFileMachine>();
foreach (var module in modules)
{
    PortableExecutableKinds peKinds;
    ImageFileMachine imageFileMachine;
    module.GetPEKind(out peKinds, out imageFileMachine);

    kinds.Add(peKinds);
    images.Add(imageFileMachine);
}

var distinctKinds = kinds.Distinct().ToList();
var distinctImages = images.Distinct().ToList();