How to find path of loader DLL? - c++

Question

I want to read binary of loader DLL of my DLL. But there is an exe and 2 DLL that I use first one (X DLL) for loadind second one (Y DLL). When I load Y dll from X DLL via exe, GetModuleFileNameA(NULL, szEXEPath, 2048); function give me just exe path. I want to get X DLL path. I could use GetModuleFileNameA("X DLL Name", szEXEPath, 2048); but I dont know name of X DLL.
When I read MSDN help for GetModuleFileName I saw the description that in below about first parameter of function.
A handle to the loaded module whose path is being requested. If this
parameter is NULL, GetModuleFileName retrieves the path of the
executable file of the current process.
I dont want to get path of executable, I just want to determine which DLL load my current DLL. Is there a way to find loader path DLL?

Answer 1

To get the "parent" dll's name, you can create a function as part of the API that is required to be called, that passes in the HMODULE handle of the parent dll.
Creating the get_current_module_handle() function below as inline and wrapping it up into a macro of some sort would simplify the process for the client code.
//... control header
inline HMODULE get_current_module_handle() {/*...*/}
#define PARENT_MODULE get_current_module_handle()
void SetControlParent(HMODULE parent);
//... client code to initialise the "parent"
SetControlParent(PARENT_MODULE);
To get the dll name (in the child), you can use a combination of the GetModuleFileNameEx and GetModuleHandleEx functions. The trick is in the GetModuleHandleEx function that allows for the module handle to be obtain via a pointer to a function (i.e. a function in the dll); particularly the use of the flag GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS.
What follows is a snippet from some code that should do the trick;
HMODULE get_current_module_handle()
{
HMODULE moduleHandle = NULL;
if (!::GetModuleHandleEx(GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS | GET_MODULE_HANDLE_EX_FLAG_UNCHANGED_REFCOUNT,
(LPCTSTR)get_current_module_handle, &moduleHandle))
throw std::runtime_error("unable to get the module handle");
return moduleHandle;
}
std::basic_string<TCHAR> get_module_name(HMODULE moduleHandle)
{
std::vector<TCHAR> filename(2048, _T('?')); // allocate some space
DWORD filenameLength = ::GetModuleFileNameEx(::GetCurrentProcess(), moduleHandle, &filename.front(), filename.size());
if (filenameLength && filenameLength < filename.size()) {
return std::basic_string<TCHAR>(&filename.front(), filenameLength);
}
return std::basic_string<TCHAR>(_T("unknown"));
}
//...
std::basic_string<TCHAR> dllname = get_module_name(get_current_module_handle()); // current dll
std::basic_string<TCHAR> parentdllname = get_module_name(parentHModule); // for "parent" dll
Note, a simplified version is reproduced above (based on the 2048 length in the OP). A recursive implementation to account for long file name is also presented (check the edits).
The dllname will be the fully qualified path of the module, hence to get the base file name, functions such as _splitpath. Alternatively, you can use GetModuleBaseName directly in the code above.
std::basic_string<TCHAR> get_module_name(HMODULE moduleHandle)
{
std::vector<TCHAR> filename(MAX_PATH, _T('?')); // MAX_PATH is 260
DWORD filenameLength = ::GetModuleBaseName(::GetCurrentProcess(), moduleHandle, &filename.front(), filename.size());
if (filenameLength && filenameLength < filename.size()) {
return std::basic_string<TCHAR>(&filename.front(), filenameLength);
}
return std::basic_string<TCHAR>(_T("unknown"));
}

Answer 2

You can use the dllpath function to define its own path and pass it as a paramater to the linked one.