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hi all

i want to learn asm inlining using codeblocks+GCC(MinGW32) and i came across this problem.
this is my code:
#include <iostream>
#include <Windows.h>
#include <winuser.h>

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

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

"movl _msg,%eax\n\t"
"pushl %eax\n\t"
"calll _printf\n\t"
"popl %eax\n\t"
"movl $0, %eax\n\t"
"movl _wCaption, %ebx\n\t"
"movl _wMsg, %ecx\n\t"
"movl $0, %edx\n\t"
"pushl %eax\n\t"
"pushl %ebx\n\t"
"pushl %ecx\n\t"
"pushl %edx\n\t"
"calll MessageBoxA\n\t"
"popl %edx\n\t"
"popl %ecx\n\t"
"popl %ebx\n\t"
"popl %eax\n\t"

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

and when i want to compile, i get:
undefined reference to `MessageBoxA'

i think its config related; because when using MinGW64, this below code compiles just fine:
#include <iostream>

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

char * const wCaption222 = "Window title";

int var = 0;

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

    "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";

i used "msys2-x86_64" to install MinGW32 and 64 and then set the directories in code blocks (creating two compiler profiles); so i don't know if messed up anything or its MinGW32's fault.

What I have tried:

googling, including various headers
Updated 21-Jun-22 21:40pm
Richard MacCutchan 1-May-22 3:16am    
You need to link the correct Windows library into the program.
reverser69 8-May-22 4:49am    
can you please specify how? I'm using C::B + GCC(MinGW)
I'll also update my question in hope of better explaining myself.
Richard MacCutchan 8-May-22 7:03am    
I have never used Code::Blocks so have no suggestions. However, if you look at the documentation for messageBoxA at MessageBoxA function (winuser.h) - Win32 apps | Microsoft Docs[^], you will see that is is defined in User32.lib. So you need to tell Code::Blocks or gcc to include that library in its link phase. A far simpler solution would be to install the latest Microsoft Visual Studio Community Edition, which is completely free.

1 solution

after searching for a month or two, I finally found out the solution:
in x86 code, APIs must be prefixed with underscore and called by their decorated name. i must call like:
calll _MessageBoxA@16

16 being the number of bytes of the function's parameter.
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