Making and Using a DLL with Assembly program

[John]

What is command line you use to assemble the ASM portion?

Make sure you are using the /Cx and /Cp options.

Also, why not use the invoke syntax, is that another restriction?
I've never seen it done the way you are doing it, but I'm pretty new to all of this anyway  :red

[tenkey]

Code Select Expand


void _stdcall ShowMessageBox()
{
  MessageBox (0,"HELLO FROM DLL","MYDLL.DLL",MB_OK);
  return;
}


... snip ...

Now, when I assemble and link the above .asm I always get that 'unresolved external 'ShowMessageBox@0' message.

If the DLL was created using MS VC++ as a '.c' program(instead of a .cpp) and the #include stdafx.h statement removed then the output MyDLL2.dll and MyDLL2.lib files will work as is in the above Assembly program but not if the DLL is compiled as a C++ program. But the problem remains that the programmers in the System Programming are always going to make DLLs using .cpp files and not .c files. So, tha't my situation.

In VC++, you need to add extern "C".

Code Select Expand


extern "C" void _stdcall ShowMessageBox()
{
  MessageBox (0,"HELLO FROM DLL","MYDLL.DLL",MB_OK);
  return;
}


If you have examples of the DLL's or its functions' declarations and uses in VB 6, it will be more revealing. You only need to supply one function that has arguments.

[Robert Collins]

In VC++, you need to add extern "C".

Code Select Expand


extern "C" void _stdcall ShowMessageBox()
{
  MessageBox (0,"HELLO FROM DLL","MYDLL.DLL",MB_OK);
  return;
}

.

Damn! You know I tried that the other day but instead of putting the extern "C" as part of the function I put it at the top of the file thinking that's where it should be so that it would be global for all functions, but it didn't work so I just abandoned that thought. It didn't occur to me to put it in the function. Thanks, tenkey, that solves my problem.

[Relvinian]

The other thing you can do to make sure you have "extern 'c'" prototype for all your .asm functions which are called from VC++ is create a header file with something like the following:

// make all functions standard "C" names and not C++ mangled.
#ifdef __cplusplus
extern "C"
{
#endif


// prototype goes here
void MyFunc();
void MyFuncWithArg(int argc);
/* etc, etc, etc */


// end specific C names
#ifdef __cplusplus
}
#endif


Then anytime you need to use one of your ASM functions, just include the appropriate header file (where you have the function declared).

Relvinian

[Robert Collins]

OK, guys, thanks to each and everyone of you I can now sleep. I convinced the Systems Programming Dept, those who make the DLLs in VC++, to include a .h file as indicated above by Relvinian. This will solve the problem for all DLLs this day forward but not so for all them that have already been written. I suppose that if the company wants to develop certain applications in Assembly then someone is just going to have to go back and re-compile the older DLLs. Probably on a need to do basis.

Anyway, that's their problem.

Thanks to all for your help. 

[Vortex]

Hi Robert,

Did you check my second example?  ( the new attachment )

[kidteam]

help me
i'm created 2 files :
  - file DLL
  - file LIB
i create by MASM32
how to use it in the C++
i'm using dev-c++ thank
file cong.asm
==============================
cong proc a:DWORD
  mov eax,a
  inc eax
  ret
cong endp
==============================
file cong.def
==============================
LIBRARY cong
EXPORTS cong
==============================
file CPP
===========================
DLLIMPORT int cong(int);
int main(void)
  {
    int a=10,b;
    b=cong(a);
  }
===========================
link error

[UtillMasm]

lib file?
how you created?

this way?
    rc.exe UtillMasm.rc
    ml.exe /c /coff UtillMasm.asm
    lib.exe /subsystem:windows UtillMasm.obj

###
or that way?

[Vortex]

i'm using dev-c++ thank

Are you referring to Bloodshed Dev-C++ ?

[UtillMasm]

oh my fo!
c++ guy!
:toothy

[kidteam]

help me
i need use masm32 to create file KIDTEAMDLL.DLL
after using in Dev-C++
code
file KIDTEAMDLL.ASM
; ¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤
    include \masm32\include\masm32rt.inc
; ¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤

    ; -------------------------------------------
    ; Build this DLL with the provided MAKEIT.BAT
    ; -------------------------------------------

      .data?
        hInstance dd ?

      .code

; «««««««««««««««««««««««««««««««««««««««««««««««««««««««««««««««««««««

LibMain proc instance:DWORD,reason:DWORD,unused:DWORD

    .if reason == DLL_PROCESS_ATTACH
      mrm hInstance, instance       ; copy local to global
      mov eax, TRUE                 ; return TRUE so DLL will start

    .elseif reason == DLL_PROCESS_DETACH

    .elseif reason == DLL_THREAD_ATTACH

    .elseif reason == DLL_THREAD_DETACH

    .endif

    ret

LibMain endp


kidteam proto
kidteam proc
  jmp qua
    nd BYTE "Ngo Hung Cuong",0
    td BYTE "Kidteam",0
  qua:
  invoke MessageBox,0,addr nd,addr td,MB_OK
  ret
kidteam endp

end LibMain
============================================
file makeit.bat
@echo off
if exist kidteamdll.obj del kidteamdll.obj
if exist kidteamdll.dll del kidteamdll.dll
\masm32\bin\ml /c /coff kidteamdll.asm
\masm32\bin\Link /SUBSYSTEM:WINDOWS /DLL /DEF:kidteamdll.def kidteamdll.obj
del kidteamdll.obj
del kidteamdll.exp
dir kidteamdll.*
pause
====================================================
file KIDTEAMDLL.DEF
LIBRARY kidteamdll
; EXPORTS [your_exported_proc_name]
EXPORTS kidteam
=====================================================
file testDLL.CPP
#include <windows.h>
#define DllImport extern "C" __declspec (dllimport)
DllImport void kidteam(void);
int WINAPI WinMain (HINSTANCE hThisInstance,
                    HINSTANCE hPrevInstance,
                    LPSTR lpszArgument,
                    int nFunsterStil)

  {
    kidteam();
    return 0;
  }
but compiler error
  [Linker error] undefined reference to `_imp__kidteam'

[hutch--]

For MASM to recognise an external procedure you need to prototype it in MASM format taking notice of the calling convention you use.

[MichaelW]

kidteam,

It looks like you are trying to create a DLL with MASM and use it from a CPP app. Your makeit.bat should be creating the import library kidteamdll.lib. You need to link this import library with your test app.

[drizz]

default calling convention for masm32 is stdcall (as per "masm32rt.inc" ".module flat,stdcall")
default calling convention for any cpp compiler is cdecl

cdecl != stdcall

solution 1
kidteam proc c

solution 2
extern "C" __declspec (dllimport)  void __stdcall kidteam(void);

use either "solution 1" or "solution 2", not both.

[kidteam]

thanhk you very much