Link problem when compiling a x86 Inline asm code with Mingw

[reverser69]

hi all

i want to write an inline asm code and call a windows API in it.
i am using code::blocks with Mingw and i get this error while trying to compile a x86 version of my code:

undefined reference to `MessageBoxA'

my x86 code:

#include <iostream>
#include <windows.h>
#include <winuser.h>



char * msg = "Hello, World!\n";
char * wMsg = "Content of the window..";
char * const wCaption = "Window title";


char * const wCaption222 = "Window title";


int var = 999999999999999;




int main (){
  std::cout << "before call" << "\n";




   asm(
    "movl $0, %%ecx\n\t"
    "movl %2, %%edx\n\t"
    "movl %4, %%ebx\n\t"
    "movl $0, %%eax\n\t"
    "pushl %%eax\n\t"
    "pushl %%ebx\n\t"
    "pushl %%edx\n\t"
    "pushl %%ecx\n\t"
    "calll MessageBoxA\n\t"
    : "=r" (var)
    : "r" (msg), "r" (wMsg) , "r" (wCaption), "r" (wCaption222)
    : "cc");


    std::cout << var << "\n";
    std::cout << "after call" << "\n";
}

i tried Mingw64, Mingw32 and Mingw multi libs, none worked for me.
i tried packages from official site, modified ones and installing with Msys2 (i don't know if i correctly installed the x86 one with Msys2 or not)

it's either i don't know how to properly add the libs or its that i don't have the right package.

interesting part is that i don't have any problem while compiling my x64 asm code with Mingw64; it compiles and runs fine:

#include <iostream>


using namespace std;


char * msg = "Hello, World!\n";
char * wMsg = "Content of the window..";
char * const wCaption = "Window title";


char * const wCaption222 = "Window title";


int var = 999999999999999;




int main (){
  std::cout << "before call" << "\n";




   asm(
    "movq $0, %%rcx\n\t"
    "movq %2, %%rdx\n\t"
    "movq %4, %%r8\n\t"
    "movq $0, %%r9\n\t"
    "callq MessageBoxA\n\t"
    : "=r" (var)
    : "r" (msg), "r" (wMsg) , "r" (wCaption), "r" (wCaption222)
    : "cc");


    std::cout << var << "\n";
    std::cout << "after call" << "\n";
}

[Salem]

Compile with the -c flag, then use the nm tool to find out what the external names actually look like.

$ g++ -c foo.cpp
$ nm -u foo.o
                 U __cxa_atexit
                 U __dso_handle
                 U _GLOBAL_OFFSET_TABLE_
                 U MessageBoxA
                 U _ZNSolsEi
                 U _ZNSt8ios_base4InitC1Ev
                 U _ZNSt8ios_base4InitD1Ev
                 U _ZSt4cout
                 U _ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc

You might need an initial underscore
"calll _MessageBoxA\n\t"

[reverser69]

Compile with the -c flag, then use the nm tool to find out what the external names actually look like.

$ g++ -c foo.cpp
$ nm -u foo.o
                 U __cxa_atexit
                 ...
                 U _ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc

You might need an initial underscore
"calll _MessageBoxA\n\t"

i cant believe i was stubling with an issue being this easy to solve.
i already tried _MessageBoxA, no use.
already tried MessageBoxA@16 too; no use.

but now, i hopelessly mixed them; _MessageBoxA@16, and it worked.

thanks for your help.

now, i have another request, and thats how can i find the full list of APIs + number of bytes taken up by their parameters e.g number 16 in above example.

[reverser69]

i cant believe it was this simple:
i have already tried prefixing with under score and also calling like MessageBoxA@16. i did these seperately.
but now, in absolute hopelessness, i mixed them e.g calll _MessageBoxA@16; compiled successfully.

now i have another favor to ask, is there any list or index anywhere to have all win API + there respective parameter size?

[flp1969]

Probably call *__imp_MessageBoxA(%%rip).