Thread: HOW TO Find right names for GetProcAddress

Hi guys, i made a .dll file ,and tried to use LoadLibrary() and GetProcAddress() to get the functions in .dll, but due to the calling conventions ,i failed to do this with all the functions,pls help

[tag]some snippets in mydll.cpp for mydll.dll[/tag]

Code:

.
...
....
......
extern "C" _declspec(dllexport) void echo1(){};
extern "C" _declspec(dllexport) void _stdcall echo2(){};

 _declspec(dllexport) void echo3(){};
 _declspec(dllexport) void _stdcall echo4(){};
......
....
..
.

i built it and got a mydll.dll file, then tried to use it in anoter .cpp file, but some wrong happened in calling GetProcAddress(),listing below:

[tag].cpp using functions in mydll.dll [/tag]

Code:

#include <windows.h>
#include "stdio.h"
int main(int argc, char** argv)
{
    HMODULE hDll;
    hDll = (HMODULE)LoadLibrary("my.dll");

    typedef void(FAR *MyEcho1)();
    MyEcho1 myecho1;
    myecho1 = (MyEcho1)GetProcAddress(hDll,"echo1");
        if(!myecho1)
        {printf("Can't find func!");}
        else
        myecho1();       //   function called successful

    typedef void(FAR *MyEcho2)();
    MyEcho2 myecho2;
    myecho2= (MyEcho2)GetProcAddress(hDll,"echo2");
        if(!myecho2)
        {printf("Can't find func!");}
        else
        myecho2();             //  function called successful


    typedef void  (FAR _cdecl *MyEcho3)();  // here is the problem, i think
    MyEcho3 myecho3;
    myecho3= (MyEcho3)GetProcAddress(hDll,"echo3");// Problem happened here        
        if(!myecho3)
        {printf("Can't find func!\n");}  //so printed error!
        else
        myecho3();

    typedef void  (FAR _stdcall *MyEcho4)();  //this block has same problem with upper one    
    MyEcho4 myecho4;
    myecho4= (MyEcho4)GetProcAddress(hDll,"echo4");
        if(!myecho4)
        {printf("Can't find func!\n")};
     else
        myecho4();


    FreeLibrary(hDll);
    return 0;
    }

[tag]wrong code,how can i do it in a right way?[/tag]

Code:

typedef void  (FAR _cdecl *MyEcho3)();  
typedef void  (FAR _stdcall *MyEcho4)();

i know that without extern "C", c++ complier(using code::blocks, but compliser is MS VC++2005/2008) changed the name of echo3 and echo4. i don't want a .DEF file, how can i make it and call it with LoadLibrary() and GetProcAddress(), thanks!

thanks vart, i konw dumpbin, but can i add "_cdecl" or "_stdcall" to the declaration(such as tpyedef void(_stdcall *MyFunc)() ) so that the machine will gengerate the right name according?

Originally Posted by Elysia

It's __cdecl and __stdcall (note the two underscores).

which is WINAPI u can either use __cdecl or WINAPI

oh yes your right its been time that i checked calling conventions.

Originally Posted by Elysia
It's __cdecl and __stdcall (note the two underscores).

is there any differences between one(_stdcall) an two(__stdcall) underscores? i tried and neither of them works...

i doubt that we cann't instruct them to find out the right name properly by telling the complier that it's a __stdcall or __cdecl convention, unless we define and output the name by a .DEF file.

and another question, when i use a DEF file, all the funcs work well and i notice that it doesn't nessary to indicate the calling convention, even the funcs have arguments with them... is it true?

it is said that calling a function by wrong convention may destroy the stack,

Code:

.dll
　__declspec(dllexport) int func(int a,int b);// use __cdecl convention
　　 
.cpp
　　typedef int (*__stdcallDLLFUNC)func(int a,int b);  //changed the calling convetion to __stdcall
　　hLib = LoadLibrary(...);

　　DLLFUNC func = (DLLFUNC)GetProcAddress(...)//changeing convention
　　result = func(1,2);//Error occurs here

so why my applicaton works well and ends normaly?(ps: i've tried both functions with argument and without arguments)

Originally Posted by albert3721

is there any differences between one(_stdcall) an two(__stdcall) underscores? i tried and neither of them works...

i doubt that we cann't instruct them to find out the right name properly by telling the complier that it's a __stdcall or __cdecl convention, unless we define and output the name by a .DEF file.

and another question, when i use a DEF file, all the funcs work well and i notice that it doesn't nessary to indicate the calling convention, even the funcs have arguments with them... is it true?

it is said that calling a function by wrong convention may destroy the stack,

Code:

.dll
　__declspec(dllexport) int func(int a,int b);// use __cdecl convention
　　 
.cpp
　　typedef int (*__stdcallDLLFUNC)func(int a,int b);  //changed the calling convetion to __stdcall
　　hLib = LoadLibrary(...);

　　DLLFUNC func = (DLLFUNC)GetProcAddress(...)//changeing convention
　　result = func(1,2);//Error occurs here

so why my applicaton works well and ends normaly?(ps: i've tried both functions with argument and without arguments)

well, it finally crashes, a wrong calling convention does destroy the stack!
and sth. flashed through my brain,

Code:

typedef void (__stdcall *MyFucn())

"__stdcall" in the snippet only indicates the calling convention. and GetProcAddress("xxx") only tries to find "xxx" in a .dll , it never converts "xxx" to" _xxx@nubmer" according to the convention indicator"__stdcall" and it never checks if xxx is built by C or C++(or it will,in c++ case, change xxx to xxx@@YG...Z)


so it's impossiable to "GetProcAddress()" a function in a .dll if one only knows the orginal name, because the original name(i.e. void echo() ) in .dll has been changed(?echo@@YAXXZ) under different circumstances (extern "C" or __stdcall,__fastcall,etc..)after being exported . is it correct?

Originally Posted by albert3721

so it's impossiable to "GetProcAddress()" a function in a .dll if one only knows the orginal name, because the original name(i.e. void echo() ) in .dll has been changed(?echo@@YAXXZ) under different circumstances (extern "C" or __stdcall,__fastcall,etc..)after being exported . is it correct?

Not impossible, just a bit more complicated.
You can examine the dll's export table and scan for the function name there. Or if you know the ordinal value of the exported function you can pass that to GetProcAddress.

Originally Posted by Codeplug

In MSVC 64 bit, when ever you dllexport a function with C linkage, using any calling convention, the name is not decorated.

I take it this is because x64 (I have no idea how IA64 works) only has 1 calling convention so there's no need for name decoration?

Originally Posted by Elysia

Where did you get IA64 from? x64 is a synonym for x86-64, AMD's 64-bit architecture.

I know, but codeplug just said "64 bit" without mentioning an architecture. And I know that x64 has just 1 calling convention. But since I don't know how IA64 does it I thought I should mention that in case someone wants to enlighten me