如何从C#调用CPU指令？

Question

我的处理器(Intel i7)支持POPCNT instruction,我想从我的C#应用​​程序中调用它.这可能吗？

我相信我在某个地方读到它不是,但如果它发现它可用,JIT会调用它但是我必须调用哪个函数可以用这样的指令代替？

Popcount在一个循环中被调用了数百万次,所以我希望能够在可能的情况下进行CPU优化.

Answer 1

你想玩火,在这里我们喜欢玩火...

class Program
{
    const uint PAGE_EXECUTE_READWRITE = 0x40;
    const uint MEM_COMMIT = 0x1000;

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

    private delegate int IntReturner();

    static void Main(string[] args)
    {
        List<byte> bodyBuilder = new List<byte>();
        bodyBuilder.Add(0xb8); // MOV EAX,
        bodyBuilder.AddRange(BitConverter.GetBytes(42)); // 42
        bodyBuilder.Add(0xc3);  // RET
        byte[] body = bodyBuilder.ToArray();
        IntPtr buf = VirtualAlloc(IntPtr.Zero, (IntPtr)body.Length, MEM_COMMIT, PAGE_EXECUTE_READWRITE);
        Marshal.Copy(body, 0, buf, body.Length);

        IntReturner ptr = (IntReturner)Marshal.GetDelegateForFunctionPointer(buf, typeof(IntReturner));
        Console.WriteLine(ptr());
    }
}

(这个小组装的例子只会返回42 ...我认为这是这个答案的完美数字:-))

最后的诀窍是:

A)您必须知道与要编写的asm相对应的操作码

B)您使用VirtualAlloc使内存页面可执行

C)在某种程度上,你可以在那里复制你的操作码

(代码来自http://www.cnblogs.com/netact/archive/2013/01/10/2855448.html)

好的...另一个是在网站上写的(减去uint- > 上的错误IntPtr dwSize),这个是它应该如何编写(或者至少它与原来的+1相比......我会封装一切在IDisposable课堂而不是使用try... finally)

class Program
{
    const uint PAGE_READWRITE = 0x04;
    const uint PAGE_EXECUTE = 0x10;
    const uint MEM_COMMIT = 0x1000;
    const uint MEM_RELEASE = 0x8000;

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

    [DllImport("kernel32.dll", SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    static extern bool VirtualProtect(IntPtr lpAddress, IntPtr dwSize, uint flAllocationType, out uint lpflOldProtect);

    [DllImport("kernel32.dll", SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    static extern bool VirtualFree(IntPtr lpAddress, IntPtr dwSize, uint dwFreeType);

    private delegate int IntReturner();

    static void Main(string[] args)
    {
        List<byte> bodyBuilder = new List<byte>();
        bodyBuilder.Add(0xb8); // MOV EAX,
        bodyBuilder.AddRange(BitConverter.GetBytes(42)); // 42
        bodyBuilder.Add(0xc3);  // RET

        byte[] body = bodyBuilder.ToArray();

        IntPtr buf = IntPtr.Zero;

        try
        {
            // We VirtualAlloc body.Length bytes, with R/W access
            // Note that from what I've read, MEM_RESERVE is useless
            // if the first parameter is IntPtr.Zero
            buf = VirtualAlloc(IntPtr.Zero, (IntPtr)body.Length, MEM_COMMIT, PAGE_READWRITE);

            if (buf == IntPtr.Zero)
            {
                throw new Win32Exception();
            }

            // Copy our instructions in the buf
            Marshal.Copy(body, 0, buf, body.Length);

            // Change the access of the allocated memory from R/W to Execute
            uint oldProtection;
            bool result = VirtualProtect(buf, (IntPtr)body.Length, PAGE_EXECUTE, out oldProtection);

            if (!result)
            {
                throw new Win32Exception();
            }

            // Create a delegate to the "function"
            // Sadly we can't use Funct<int>
            var fun = (IntReturner)Marshal.GetDelegateForFunctionPointer(buf, typeof(IntReturner));

            Console.WriteLine(fun());
        }
        finally
        {
            if (buf != IntPtr.Zero)
            {
                // Free the allocated memory
                bool result = VirtualFree(buf, IntPtr.Zero, MEM_RELEASE);

                if (!result)
                {
                    throw new Win32Exception();
                }
            }
        }
    }
}