Build and override a simple Winelib DLL

Question

I have a Windows executable that load a library and I want to create a Winelib DLL that will overide the Windows DLL. It's been 2 days that I search and try but it won't work ! Please help me !

Basically I create mydll.c and mydll.spec to build the Winelib DLL with the command:

winegcc -m32 -shared -o mydll.dll mydll.c mydll.spec

Now I have mydll.dll.so and I want to override mydll.dll (both are at the same place) What should I do ? I try to rename mydll.dll but I got a Page Fault when the function is called ! I also tried to configure the override with winecfg or set environment variables like WINEDLLPATH. I don't understand how to proceed.

---

How I load the library in my Windows executable

HINSTANCE DllHandle;
char str[255];
typedef int(__stdcall * tfp)(char * const);
DllHandle = LoadLibrary("mydll.dll");
tfp fp = (tfp)GetProcAddress(DllHandle, "myfunc");
fp(str);
FreeLibrary(DllHandle);

mydll.spec

@ stdcall myfunc(str)

mydll.c

#include <windef.h>

int WINAPI myfunc(char * str)
{
  strcpy(str, "myfunc from the Winelib DLL");
  return 0;
}

Answer 1

I was able to get this to work but had to make the following changes.

I was using wine5 on Ubuntu, where is seems the default install is 64bit. I had to rename wine's executable first as it was using the 32bit call by mistake and that meant it would not work with the 64bit dll.

install wine-tools (for winegcc)

apt-get install wine-tools

Fix wine64 (as the exe seems to load wine32 and then error)

cd /usr/lib/wine
mv wine wine32
ln -s wine64 wine

Makefile

all:    mydll.dll.so testmydll.exe

mydll.dll.so:   mydll.c mydll.spec
        winegcc -shared -o mydll.dll mydll.c mydll.spec

testmydll.exe:  testmydll.c
        winegcc -mno-cygwin -o testmydll testmydll.c

clean:
        rm -f *.so
        rm -f *.exe
        rm -f *~

Also, there is a mistake in your code, which I corrected. The lack of a __stdcall and the name of the DLL.

Answer 2

Use WINEDEBUG=+module to debug DLL loading problems.

I don't believe Wine searches for native .dll.so files outside of a single folder but the code is in dlls/ntdll/loader.c:load_builtin_dll if you want to check yourself.