x86/x64 CPUID in C#

Question

Related to my other question, please help me debug \"An unhandled exception of type \'System.AccessViolationException\' occurred in Unknown Module. Additional information:

Answer 1

I decided to improve your answer. It does not need unsafe to compile anymore, and it only needs two assembly blocks in order to be able to read out any and all cpuid blocks, because it just writes eax/ebx/ecx/edx to a 16-byte byte array.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Reflection;
using System.Runtime.InteropServices;

namespace CpuID
{
    public class CpuID : IDisposable
    {
        [UnmanagedFunctionPointerAttribute(CallingConvention.Cdecl)]
        public delegate void CpuIDDelegate(int level, byte[] buffer);

        [DllImport("kernel32.dll", SetLastError = true)]
        private static extern IntPtr VirtualAlloc(
            IntPtr lpAddress,
            UIntPtr dwSize,
            AllocationType flAllocationType, 
            MemoryProtection flProtect
        );

        [DllImport("kernel32")]
        private static extern bool VirtualFree(
                IntPtr lpAddress,
                UInt32 dwSize,
                UInt32 dwFreeType
        );

        [Flags()]
        public enum AllocationType : uint
        {
            COMMIT = 0x1000,
            RESERVE = 0x2000,
            RESET = 0x80000,
            LARGE_PAGES = 0x20000000,
            PHYSICAL = 0x400000,
            TOP_DOWN = 0x100000,
            WRITE_WATCH = 0x200000
        }

        [Flags()]
        public enum MemoryProtection : uint
        {
            EXECUTE = 0x10,
            EXECUTE_READ = 0x20,
            EXECUTE_READWRITE = 0x40,
            EXECUTE_WRITECOPY = 0x80,
            NOACCESS = 0x01,
            READONLY = 0x02,
            READWRITE = 0x04,
            WRITECOPY = 0x08,
            GUARD_Modifierflag = 0x100,
            NOCACHE_Modifierflag = 0x200,
            WRITECOMBINE_Modifierflag = 0x400
        }

        private CpuIDDelegate cpuIdDelg;

        private IntPtr codePointer;

        // void x86CpuId(int level, byte* buffer) 
        // {
        //    eax = level
        //    cpuid
        //    buffer[0] = eax
        //    buffer[4] = ebx
        //    buffer[8] = ecx
        //    buffer[12] = edx
        // }
        private byte[] x86CodeBytes = 
        {
            0x55,                   // push        ebp  
            0x8B, 0xEC,             // mov         ebp,esp
            0x53,                   // push        ebx  
            0x57,                   // push        edi

            0x8B, 0x45, 0x08,       // mov         eax, dword ptr [ebp+8] (move level into eax)
            0x0F, 0xA2,              // cpuid

            0x8B, 0x7D, 0x0C,       // mov         edi, dword ptr [ebp+12] (move address of buffer into edi)
            0x89, 0x07,             // mov         dword ptr [edi+0], eax  (write eax, ... to buffer)
            0x89, 0x5F, 0x04,       // mov         dword ptr [edi+4], ebx 
            0x89, 0x4F, 0x08,       // mov         dword ptr [edi+8], ecx 
            0x89, 0x57, 0x0C,       // mov         dword ptr [edi+12],edx 

            0x5F,                   // pop         edi  
            0x5B,                   // pop         ebx  
            0x8B, 0xE5,             // mov         esp,ebp  
            0x5D,                   // pop         ebp 
            0xc3                    // ret
        };

        private byte[] x64CodeBytes = 
        {
            0x53,                       // push rbx    this gets clobbered by cpuid

            // rcx is level
            // rdx is buffer.
            // Need to save buffer elsewhere, cpuid overwrites rdx
            // Put buffer in r8, use r8 to reference buffer later.

            // Save rdx (buffer addy) to r8
            0x49, 0x89, 0xd0,           // mov r8,  rdx

            // Move ecx (level) to eax to call cpuid, call cpuid
            0x89, 0xc8,                 // mov eax, ecx
            0x0F, 0xA2,                 // cpuid

            // Write eax et al to buffer
            0x41, 0x89, 0x40, 0x00,     // mov    dword ptr [r8+0],  eax
            0x41, 0x89, 0x58, 0x04,     // mov    dword ptr [r8+4],  ebx
            0x41, 0x89, 0x48, 0x08,     // mov    dword ptr [r8+8],  ecx
            0x41, 0x89, 0x50, 0x0c,     // mov    dword ptr [r8+12], edx

            0x5b,                       // pop rbx
            0xc3                        // ret
        };

        public CpuID()
        {
            Compile();
        }

        ~CpuID()
        {
            Dispose(false);
        }

        private void Compile()
        {
            byte[] codeBytes;

            if (IntPtr.Size == 4)
            {
                codeBytes = x86CodeBytes;
            }
            else
            {
                codeBytes = x64CodeBytes;
            }

            this.codePointer = VirtualAlloc(
                IntPtr.Zero,
                new UIntPtr((uint)codeBytes.Length),
                AllocationType.COMMIT | AllocationType.RESERVE,
                MemoryProtection.EXECUTE_READWRITE
            );

            Marshal.Copy(codeBytes, 0, this.codePointer, codeBytes.Length);

            this.cpuIdDelg = (CpuIDDelegate)Marshal.GetDelegateForFunctionPointer(this.codePointer, typeof(CpuIDDelegate));
        }

        public void Invoke(int level, byte[] buffer)
        {
            GCHandle handle = default(GCHandle);
            if (buffer.Length < 16)
            {
                throw new ArgumentException("buffer must be at least 16 bytes long");
            }

            try
            {
                handle = GCHandle.Alloc(buffer, GCHandleType.Pinned);

                this.cpuIdDelg(level, buffer);
            }
            finally
            {
                if (handle != default(GCHandle))
                {
                    handle.Free();
                }
            }
        }

        public void Dispose()
        {
            Dispose(true);
        }

        public void Dispose(bool disposing)
        {
            if (this.codePointer != IntPtr.Zero)
            {
                VirtualFree(this.codePointer, 0, 0x8000);
                this.codePointer = IntPtr.Zero;
            }
        }

    }
}