Monday, June 1, 2009

Calling CPUID from PowerShell for Intel VT

I was trying to work out whether the Intel VT (VMX) extensions had been enabled on a server and whether the server support the SSE4.1 and SSE4.2 processor instructions - without having to reboot the server to check the BIOS. I ended up 'writing' a PowerShell script that compiles some C# to call a DLL written in assembler which has run the CPUID instruction and returned the results. Note that I didn't really write any of this, the PowerShell script compiling and running the C# is from the reference below, as is the actual C$ and asm dll.

Does this seem like a lot of effort? Sure does, but unfortunately the simple method - using Win32_Processor.ProcessorID was useless in this example, as for some reason MS chose to only return the EAX and EDX registers, whereas the bits I was after were returned in ECX. There may also be other ways to achieve this through PowerShell/.Net framework, rather than compiling c# to call unmanaged code.

Below is the PowerShell script, which contains the inline C# that is compiled and executed, which in turn requires the dll, using the EFLAGS register to confirm support and the CPUID instruction with eax=1 (if further supported) to query feature information from the CPU.

The original c# and asm dll: (see below for the hex text stream)

The compile-csharp function: (adding the -unsafe parameter to allow pointer use)

# Description:
#  Call the CPUID function from an external DLL through C# inline code.
#  Report whether Intel VT (VMX) is supported, bit 5 of the ECX register returned from CPUID eax=1 call.
#  Note that WMI Win32_Processor:ProcessID contains the results of a call to CPUID - except that it only contains EAX and EDX, Intel VT (what I was after) is in ECX
# Author:
#  Wayne Martin, note that I didn't write any of this code, the inline C# was from the monad reference below, and the CPUID DLL and C# was from the first reference

# cpuid.dll and the namespace from:
# Intel cpuid:

function Compile-Csharp ([string] $code, $FrameworkVersion="v2.0.50727",
    $cp = new-object Microsoft.CSharp.CSharpCodeProvider
    $cpar = New-Object System.CodeDom.Compiler.CompilerParameters
    $cpar.CompilerOptions = "-unsafe"      # unsafe to compile the code which uses pointers in the DLL call
    $cpar.GenerateInMemory = $true
    $cpar.GenerateExecutable = $false
    $cpar.OutputAssembly = "custom"
    # $cpar.ReferencedAssemblies.AddRange($refs)
    $cr = $cp.CompileAssemblyFromSource($cpar, $code)

    if ( $cr.Errors.Count)
        $codeLines = $code.Split("`n");
        foreach ($ce in $cr.Errors)
            write-host "Error: $($codeLines[$($ce.Line - 1)])"
            write-host $ce
           # $ce out-default
        Throw "INVALID DATA: Errors encountered while compiling code"

$code = @'
namespace CPUID
 using System;
 using System.Runtime.InteropServices;
 using System.Text;

 public class cpuid
  private cpuid()

     public static extern bool CPUIDIsSupported();

     private unsafe static extern bool __cpuid
            (uint function, 
             int* eax, 
             int* ebx, 
             int* ecx, 
             int* edx);

  // Invoke __cpuid function
  public unsafe static bool Invoke
      (uint level, 
       out int eax, 
       out int ebx, 
       out int ecx, 
       out int edx)
   int __eax = 0;
   int __ebx = 0;
   int __ecx = 0;
   int __edx = 0;

   if (__cpuid(level, &__eax, &__ebx, &__ecx, &__edx))
    eax = __eax;
    ebx = __ebx;
    ecx = __ecx;
    edx = __edx;

    return true;
    eax = 0;
    ebx = 0;
    ecx = 0;
    edx = 0;

    return false;


compile-CSharp $code
$eax = ""
$ebx = ""
$ecx = ""
$edx = ""
[CPUID.CPUID]::Invoke(1, [ref]$eax, [ref]$ebx, [ref]$ecx, [ref]$edx) 

$INTEL_CPUID_VT_FLAG = 0x0020                                                           # bit 5 of ECX returned from CPUID EAX=1
$INTEL_CPUID_SSE41 = 0x80000                                                            # bit 19 of ECX returned from CPUID EAX=1
$INTEL_CPUID_SSE42 = 0x100000                                                           # bit 20 of ECX returned from CPUID EAX=1
$INTEL_CPUID_XD = 0x00100000

write-output ("Intel VT: " + ($ecx -band $INTEL_CPUID_VT_FLAG) )                        # Does this processor support Intel VT / VMX?
write-output ("SSE 4.1: " + ($ecx -band $INTEL_CPUID_SSE41) )                           # Does this processor support SSE 4.1?
write-output ("SSE 4.2: " + ($ecx -band $INTEL_CPUID_SSE42) )                           # Does this processor support SSE 4.2?
write-output ("eXecute Disable: " + ($edx -band $INTEL_CPUID_XD) )                      # Does this processor support XD?

Note that in a previous post, I have written two powershell scripts, one to convert binary to a hex string, and vice versa. The following stream is the cpuid.dll file, if you write it to cpuid.txt and run the following command it will create the dll:

Powershell . .\HexStringToBinary.ps1 cpuid.txt cpuid.dll


Wayne's World of IT (WWoIT), Copyright 2009 Wayne Martin. 

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About Me

I’ve worked in IT for over 13 years, and I know just about enough to realise that I don’t know very much.