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 took @antiduh's code and refactored it into a static method, so there is no object lifecycle to manage. This is slower because the ASM code isn't reused between calls to Invoke(), but the tradeoff of speed for simplicity makes sense for my use case. This new version can call CPUID 1000 times in 15 milliseconds on my machine.

Thanks for the wonderful code guys!

public static class CpuID {

    public static byte[] Invoke(int level) {
        IntPtr codePointer = IntPtr.Zero;
        try {
            // compile
            byte[] codeBytes;
            if (IntPtr.Size == 4) {
                codeBytes = x86CodeBytes;
            } else {
                codeBytes = x64CodeBytes;
            }

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

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

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

            // invoke
            GCHandle handle = default(GCHandle);
            var buffer = new byte[16];

            try {
                handle = GCHandle.Alloc(buffer, GCHandleType.Pinned);
                cpuIdDelg(level, buffer);
            } finally {
                if (handle != default(GCHandle)) {
                    handle.Free();
                }
            }

            return buffer;
        } finally {
            if (codePointer != IntPtr.Zero) {
                VirtualFree(codePointer, 0, 0x8000);
                codePointer = IntPtr.Zero;
            }
        }
    }

    [UnmanagedFunctionPointerAttribute(CallingConvention.Cdecl)]
    private 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()]
    private enum AllocationType : uint {
        COMMIT = 0x1000,
        RESERVE = 0x2000,
        RESET = 0x80000,
        LARGE_PAGES = 0x20000000,
        PHYSICAL = 0x400000,
        TOP_DOWN = 0x100000,
        WRITE_WATCH = 0x200000
    }

    [Flags()]
    private 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
    }

    // Basic ASM strategy --
    // void x86CpuId(int level, byte* buffer) 
    // {
    //    eax = level
    //    cpuid
    //    buffer[0] = eax
    //    buffer[4] = ebx
    //    buffer[8] = ecx
    //    buffer[12] = edx
    // }

    private readonly static 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 readonly static 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
    };
}