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Using Unmanaged code and assembler in C#

, 22 Sep 2001
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This article describes how to call unmanaged code and assembler in C# using DLLs
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Introduction

The first question is why we call unmanaged code before we discuss how to call unmanaged code.

There are possibly two reasons to call unmanaged code

  1. You want to reuse your code which is already written in unmanaged environment e.g. VC 6.0
  2. You want to Perform some low level work i.e. (need in line assembly in your program)

How to call unmanaged code

The first time I saw this topic in Tom Archer's "Inside C#" which explain how to call unmanaged DLL from the C#

Program 1

// Sample program to call unmanaged code
using System;
using System.Runtime.InteropServices;

class PInvoke1App
{
    [DllImport("user32.dll")]
    static extern int MessageBoxA(int hWnd, string strMsg, string strCaption, int iType);

    public static void Main() 
    {
        MessageBoxA(0, "Hello, World!", "This is called from a C# app!", 0);
    }
}
Then I tried to make my own DLL and call that DLL from my Application

Program 2

// Dll1.cpp
// Written by Zeeshan Amjad

#include <windows.h>

BOOL __stdcall DllMain(HINSTANCE hInst, DWORD dwReason, LPVOID lpReserved) {
	return TRUE;
}

__declspec(dllexport) void __stdcall Message(char* p_szMessage) {
	MessageBox(NULL, p_szMessage, "Message from DLL", MB_OK);
}
And my C# Program is:

Program 3

// Native2.cs
// Written by Zeeshan Amjad

using System;
using System.Runtime.InteropServices;

class MainClass {
	[DllImport("Dll1.dll")]
	static extern void Message(string msg);
	
	public static void Main() {
		Message("Hello world");
	}
};
Now I ran program and my program crashed because it can not find DLL1.dll - either in current directory nor in the path. It threw a DllNotFoundException. To handle this I had to catch this exception. So I change my program little bit to:

Program 4

// Native3.cs
// Written by Zeeshan Amjad

using System;
using System.Runtime.InteropServices;

class MainClass {
	[DllImport("Dll1.dll")]
	static extern void Message(string msg);
	
	public static void Main() {
		try {
			Message("Hello world");
		}
		catch(DllNotFoundException e) {
			Console.WriteLine(e.ToString());
		}
	}
};
And also copied the DLL1.dll to the current folder to avoid this exception.

Now again my program crashed when I tried to run it. This time it threw a EntryPointNotFoundException. To handle this more elegantly I should also catch this and display an error message for this exception rather than crash the program. This is new version of the program:

Program 5

// Native4.cs
// Written by Zeeshan Amjad

using System;
using System.Runtime.InteropServices;

class MainClass {
	[DllImport("Dll1.dll")]
	static extern void Message(string msg);
	
	public static void Main() {
		try {
			Message("Hello world");
		}
		catch(DllNotFoundException e) {
			Console.WriteLine(e.ToString());
		}
		catch(EntryPointNotFoundException e) {
			Console.WriteLine(e.ToString());
		}
	}
};
This program now give this error message
System.EntryPointNotFoundException: Unable to find an entry point named Message in DLL Dll1.dll.
   at MainClass.Message(String msg)
   at MainClass.Main()
The problem is not in this C# program. In fact when you write a function in C++ the compiler decorates the function name to enable function overloading. The function which exports by DLL is not Message. To get the exact name type 

dumpbin -exports dll1.dll  

at command prompt. The part of output of this utility is

    ordinal hint RVA      name

          1    0 00001005 ?Message@@YGXPAD@Z
There isn't any standard way of decorating function names, so we should tell the compiler not to decorate function name.

This is revised version of DLL code.

Program 6

// Dll1.cpp
// Written by Zeeshan Amjad

#include <windows.h>

BOOL __stdcall DllMain(HINSTANCE hInst, DWORD dwReason, LPVOID lpReserved) {
	return TRUE;
}

extern "C" __declspec(dllexport) void __stdcall Message(char* p_szMessage) {
	MessageBox(NULL, p_szMessage, "Message from DLL", MB_OK);
}
extern "C" is used to tell the compiler not to decorate the function name.

Now if we see the function name from the dumpbin utility its output looks like this.

    ordinal hint RVA      name

          1    0 0000100A _Message@4
Here @ shows the function uses the standard calling convention and 4 shows the number of bytes pushed on the stack for parameters. In a 32 bit environment like windows 9x and NT/2000 the address is stored in 32 bits i.e. 4 bytes. It means there is only one parameter in the stack  - in other words this function takes only one parameter.

Now the above C# Program works fine without any change and displays a message box with Text "Hello world" with the caption "Message from DLL"

How to call assembly in C#

Let's do an experiment with inline assembly in a DLL. I can not call assembly language from C# but I know I can call unmanaged DLLs from C#. I'll make a DLL which calculates the speed of CPU, vendor name, Family, Model and Stepping of CPU using in line assembly language.

Program 7

// SysInfo.cpp
// written by Zeeshan Amjad

#include "SysInfo.h"

BOOL __stdcall DllMain(HINSTANCE hInst, DWORD dwReason, LPVOID lpReserved) {
	return  TRUE;
}

extern "C" __declspec(dllexport) int __stdcall getCPUSpeed() {
	LARGE_INTEGER ulFreq, ulTicks, ulValue, ulStartCounter, ulEAX_EDX, ulResult;

	// it is number of ticks per seconds
	QueryPerformanceFrequency(&ulFreq);

	// current valueofthe performance counter
	QueryPerformanceCounter(&ulTicks);

	// calculate one second interval
	ulValue.QuadPart = ulTicks.QuadPart + ulFreq.QuadPart;

	// read time stamp counter
	// this asm instruction load the highorder 32 bit of the register into EDX
	// and the lower order 32 bits into EAX
	_asm {
		rdtsc
		mov ulEAX_EDX.LowPart, EAX
		mov ulEAX_EDX.HighPart, EDX
	}

	// start no of ticks
	ulStartCounter.QuadPart = ulEAX_EDX.QuadPart;

	// loop for 1 second
	do {
		QueryPerformanceCounter(&ulTicks);
	} while (ulTicks.QuadPart <= ulValue.QuadPart);

	// get the actual no of ticks
	_asm {
		rdtsc
		mov ulEAX_EDX.LowPart, EAX
		mov ulEAX_EDX.HighPart, EDX
	}

	// calculate result
	ulResult.QuadPart = ulEAX_EDX.QuadPart - ulStartCounter.QuadPart;

	return (int)ulResult.QuadPart / 1000000;
}

extern "C" __declspec(dllexport) char* __stdcall getCPUType() {
	static char pszCPUType[13];
	memset(pszCPUType, 0, 13);

	_asm {
		mov eax, 0
		cpuid

		// getting information from EBX
		mov pszCPUType[0], bl
		mov pszCPUType[1], bh

		ror  ebx, 16
		mov pszCPUType[2], bl
		mov pszCPUType[3], bh

		// getting information from EDX
		mov pszCPUType[4], dl
		mov pszCPUType[5], dh

		ror  edx, 16
		mov pszCPUType[6], dl
		mov pszCPUType[7], dh

		// getting information from ECX
		mov pszCPUType[8], cl
		mov pszCPUType[9], ch

		ror  ecx, 16
		mov pszCPUType[10], cl
		mov pszCPUType[11], ch
	}

	pszCPUType[12] = '\0';

	return pszCPUType;
}

extern "C" __declspec(dllexport) int __stdcall getCPUFamily() {
	int retVal;

	_asm {
		mov eax, 1
		cpuid
		mov retVal, eax
	}

	return (retVal >> 8);
}

extern "C" __declspec(dllexport) int __stdcall getCPUModel() {
	int retVal;

	_asm {
		mov eax, 1
		cpuid
		mov retVal, eax
	}

	return ((retVal >> 4 ) & 0x0000000f);
}

extern "C" __declspec(dllexport) int __stdcall getCPUStepping() {
	int retVal;

	_asm {
		mov eax, 1
		cpuid
		mov retVal, eax
	}

	return (retVal & 0x0000000f);
}
Here is a simple client of this DLL which is written in VC++ to check the functionality of this.

Program 8

// Client1.cpp
// Written by Zeeshan Amjad

#include <iostream.h>
#include "SysInfo.h"

#pragma comment(lib, "SysInfo.lib")

int main() {
	cout << "CPU Speed = " << getCPUSpeed() << endl;
	cout << "CPU Type = " << getCPUType() << endl;
	cout << "CPU Family = " << getCPUFamily() << endl;
	cout << "CPU Model = " << getCPUModel() << endl;
	cout << "CPU Stepping = " << getCPUStepping() << endl;
	return 0;
}
Now I m going to write the same client in C#.

Program 9

// Native5.cs
// Written by Zeeshan Amjad

using System;
using System.Runtime.InteropServices;

class MainClass {
	[DllImport("SysInfo.dll")]
	static extern int getCPUSpeed();
	
	[DllImport("SysInfo.dll")]
	static extern string getCPUType();
	
	[DllImport("SysInfo.dll")]
	static extern int getCPUFamily();
	
	[DllImport("SysInfo.dll")]
	static extern int getCPUModel();

	[DllImport("SysInfo.dll")]
	static extern int getCPUStepping();
	
	// main program
	public static void Main() {
		
		// get CPU Speed
		try {
			int iCPUSpeed = getCPUSpeed();
			Console.WriteLine("CPU Speed = {0}", iCPUSpeed.ToString());
		}
		catch (DllNotFoundException e) {
			Console.WriteLine(e.ToString());
		}
		catch (EntryPointNotFoundException e) {
			Console.WriteLine(e.ToString());
		}
		
		// get CPU Type
		try {
			string strType = getCPUType();
			Console.WriteLine("CPU Type = {0}", strType);
		}
		catch (DllNotFoundException e) {
			Console.WriteLine(e.ToString());
		}
		catch (EntryPointNotFoundException e) {
			Console.WriteLine(e.ToString());
		}
		
		// get CPU Family
		try {
			int iFamily = getCPUFamily();
			Console.WriteLine("CPU Family = {0}", iFamily.ToString());
		}
		catch (DllNotFoundException e) {
			Console.WriteLine(e.ToString());
		}
		catch (EntryPointNotFoundException e) {
			Console.WriteLine(e.ToString());
		}
		
		// get CPU Model
		try {
			int iModel = getCPUModel();
			Console.WriteLine("CPU Model = {0}", iModel.ToString());
		}
		catch (DllNotFoundException e) {
			Console.WriteLine(e.ToString());
		}
		catch (EntryPointNotFoundException e) {
			Console.WriteLine(e.ToString());
		}

		// get CPU Stepping
		try {
			int iStepping = getCPUStepping();
			Console.WriteLine("CPU Stepping = {0}", iStepping.ToString());
		}
		catch (DllNotFoundException e) {
			Console.WriteLine(e.ToString());
		}
		catch (EntryPointNotFoundException e) {
			Console.WriteLine(e.ToString());
		}
	}
};
I write GUI for this program. The image below shows the output.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Zeeshan Amjad
Software Developer (Senior) Bloomberg LP
United States United States
Working as a Sr C++ Developer at Bloomberg LP

Comments and Discussions

 
Questionhow do you import a method from unmanaged Dll class Pinmemberteshman24-Apr-14 19:02 
Generalgarbled character strings (chinese characters) [modified] PinmemberKrischu13-Aug-10 0:39 
GeneralVS2008 get BadImageFormatException when loading Dll1.dll [modified] PinmemberKrischu12-Aug-10 22:49 
Generalassembly in c# Pingroupmetyouba30-Jun-10 13:34 
Generaldll file Pingroupmetyouba24-Jun-10 6:29 
plz i want to ask how to make dll file on c++? is it from MFC smart device dll or from MFC dll or from console application on c++
plz in program 2 where is the body of the dll?
GeneralRe: dll file PinmemberZeeshan Amjad24-Jun-10 8:50 
Generalunmanaged code with classes and interfaces PinmemberBatulKaleem15-Jun-10 5:00 
QuestionIs there any way to access exported variables? PinmemberBug Me Not13-Oct-09 20:59 
AnswerRe: Is there any way to access exported variables? Pinmemberpk_fox7-Mar-10 22:19 
QuestionMethod With Cstring Pinmemberrajeev.abes17-Sep-09 20:49 
GeneralNice Article Pinmembersanthosh55516-Sep-09 7:45 
GeneralMarshalling: Using native DLLs in .NET Pinmembermeukjeboer10-Sep-08 5:16 
GeneralI have the same error, DllNotFoundException but is not cured after i tried try and catch. Pinmembersharp_k20-May-08 15:08 
GeneralRe: I have the same error, DllNotFoundException but is not cured after i tried try and catch. Pinmembereduardna13-Jun-08 4:31 
GeneralRe: I have the same error, DllNotFoundException but is not cured after i tried try and catch. Pinmembersharp_k13-Jun-08 7:39 
GeneralRe: I have the same error, DllNotFoundException but is not cured after i tried try and catch. Pinmembereduardna18-Jun-08 4:06 
GeneralRe: I have the same error, DllNotFoundException but is not cured after i tried try and catch. Pinmembersharp_k18-Jun-08 4:49 
GeneralGet CPU temperature with assembly and/or C++ PinmemberJavalang31-Jul-07 5:48 
GeneralC lib on C# PinmemberBandoleiro11-Dec-06 4:37 
GeneralRe: C lib on C# Pinmembermarkus.md5-Jan-09 7:23 
GeneralExcellent Piece of Example Pinmemberbilalabbas29-May-06 21:11 
GeneralCreating Managed wrappers in C++ for unmanged C++ dll Pinmembersrinin00810-Feb-06 1:31 
GeneralStopping dll Pinmembertoticow29-Dec-04 18:13 
GeneralRe: Stopping dll PinmemberPeregrine Falcon20-Jul-05 4:26 
GeneralRe: Stopping dll Pinmembereduardna13-Jun-08 4:34 

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