Good day, everyone!
I wrote some dll, which I use in my project. In constuctor of class I load library lib = LoadLibrary(L"library.dll");, in destructor I free it using
if (lib)
FreeLibrary(lib);
Some times applications blocks when FreeLibrary is called, what I am doing wrong?
I implement dllMain but this is not solve my problem =(
in .h file
BOOL WINAPI DllMain( HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpReserved );
extern "C" {
static projector::CProjCorrectionsClient* corrections;
void DLLPROJECTOR_EXPORT CorrectionsInit (const char* configFile);
void DLLPROJECTOR_EXPORT CorrectionsApply ();
}
in cpp file
BOOL WINAPI DllMain( HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpReserved )
{
switch( fdwReason )
{
case DLL_PROCESS_ATTACH:
qDebug() << "DLL_PROCESS_ATTACH";
corrections = new projector::CProjCorrectionsClient();
break;
case DLL_THREAD_ATTACH:
break;
case DLL_THREAD_DETACH:
break;
case DLL_PROCESS_DETACH:
qDebug() << "DLL_PROCESS_DEATTACH";
delete corrections;
qDebug() << "Corrections delete success";
break;
}
qDebug() << "Out side dllmain switch";
return TRUE;
}
On console I see this messages:
DLL_PROCESS_ATTACH
Out side dllmain switch
<...>
Try to release library
DLL_PROCESS_DEATTACH
Corrections delete success
Out side dllmain switch
There is no message after FreeLibrary call and applications freeze.
Make sure you are not waiting for some thread inside DLL_PROCESS_DETACH.
When DllMain is called, system aquires internal critical section, which can cause deadlock if your code inside DllMain waits for some thread T to finish, this thread when finishing will also want to do DLL_PROCESS_DETACH, but since system critical section is aquired it will wait infinitelly causing deadlock.
The question should maybe be - 'what is the dll doing wrong?'. If the library is going to be unloaded because its ref count has reached zero then FreeLibrary will give the dll a chance to clean up, and will call DllMain with DLL_PROCESS_DETACH. Perhaps try debugging the dll to see whats going on when this event occurs.
Also if there is any static data in the DLL that could run destructors then perhaps the issue lies there.
Related
I am trying to load a DLL from Console Application. The simple console application is shown below:
#include <iostream>
#include <windows.h>
int main(){
HMODULE handleDll = LoadLibraryA("C:\\Tools\\TestDLL.dll");
if (handleDll)
{
std::cout << "DLL Loaded at Address: " << handleDll << std::endl;
}
FreeLibrary(handleDll);
}
The DLL is supposed to a POP a MessageBox which it does but just flashes on the screen instead of waiting for user input. The DLL code is below:
// dllmain.cpp : Defines the entry point for the DLL application.
#include "pch.h"
#include <Windows.h>
DWORD WINAPI ThreadProc( __in LPVOID lpParameter )
{
MessageBox(NULL, L"Hi From The Thread!", L"Pop a Box!", MB_OK);
return 0;
}
extern "C" __declspec(dllexport)
VOID PopMessageBox()
{
DWORD ThreadID;
HANDLE handleThread;
handleThread = CreateThread(NULL, 0, ThreadProc, 0, 0, &ThreadID);
CloseHandle(handleThread);
}
BOOL APIENTRY DllMain( HMODULE hModule,
DWORD ul_reason_for_call,
LPVOID lpReserved
)
{
switch (ul_reason_for_call)
{
case DLL_PROCESS_ATTACH:
PopMessageBox();
break;
case DLL_THREAD_ATTACH:
case DLL_THREAD_DETACH:
case DLL_PROCESS_DETACH:
break;
}
return TRUE;
}
My question is..how do I make the code in the thread function fully execute without prematurely terminating or causing painful deadlocks? Apologies for my imperfect English and inexperience.
The reason is that you are doing something unsafe in your DllMain: you are calling CreateThread.
You are very limited in what you can do from within DllMain in response to a process attach, a fact that the documentation calls out:
There are significant limits on what you can safely do in a DLL entry point. See General Best Practices for specific Windows APIs that are unsafe to call in DllMain. If you need anything but the simplest initialization then do that in an initialization function for the DLL. You can require applications to call the initialization function after DllMain has run and before they call any other functions in the DLL.
The warning links you to "General Best Pratices" which, among other things, says to "[c]all CreateThread. Creating a thread can work if you do not synchronize with other threads, but it is risky."
Even without the risks associated with synchronizing with other threads, this code is flakey in other ways: for example, your main simply calls FreeLibrary and exits. The thread you had spawned in the DLL, which may literally be mid-execution, will have the code it's supposed to run unmapped. You're literally pulling the rug out from under it!
I would like to attach my DLL to a game to add more features.
The DLL is 95% done, the problem is in finding the best and easy way to load this DLL from within the game.
My idea is to use this technique:
dinput_ori.dll (old dll)
dinput.dll (my dll that points to dinput_ori.dll)
I don't need to access any members of original DLL, but only load my new DLL.
I am searching for a generic DLL source code that can do the following:
bool WINAPI DllMain(HMODULE hModule, DWORD dwReason, LPVOID lpReserved)
{
std::string DLLFileOri = "dinput_ori.dll";
switch (dwReason)
{
case DLL_PROCESS_ATTACH:
// Load dll
LoadOriDll(DLLFileOri);
MsgBox("This DLL was loaded.");
break;
case DLL_PROCESS_DETACH:
// Close the DLL
UnloadOriDll(DLLFileOri);
break;
}
return true;
}
In this case the name of my DLL is "dinput.dll".
Is there a generic source code that can do this ?
Thanks!
This question already has answers here:
How does RunDll32 work?
(2 answers)
Closed 8 years ago.
I have created a dead-simple DLL in Visual Studio 2010, a win32 project of type DLL.
Then I changed the DllMain to this:
BOOL APIENTRY DllMain( HMODULE hModule,
DWORD ul_reason_for_call,
LPVOID lpReserved
)
{
switch (ul_reason_for_call)
{
case DLL_PROCESS_ATTACH:
MessageBox(0,L"Hey there!",0,0);
break;
case DLL_THREAD_ATTACH:
case DLL_THREAD_DETACH:
case DLL_PROCESS_DETACH:
break;
}
return TRUE;
}
and I used rundll32 vahid-win32.dll,dllmain to run it. Message box shows, but after that it gives
Error in vahid-win32.dll
Missing entry: dllmain
What is wrong with my DLL? or with me? :-)
Thanks in advance
Your messagebox doesn't come from you passing DllMain function name. Rather it is automatically called. But Rundll32 looking for a export function with name DllMain with dllexport declaration as given below.
BOOL APIENTRY DllMain( HMODULE hModule,
DWORD ul_reason_for_call,
LPVOID lpReserved
)
{
switch (ul_reason_for_call)
{
case DLL_PROCESS_ATTACH:
MessageBox(0,L"Hey there!",0,0);
break;
case DLL_THREAD_ATTACH:
case DLL_THREAD_DETACH:
case DLL_PROCESS_DETACH:
break;
}
return TRUE;
}
extern "C" __declspec(dllexport) void mydllmain()
{
MessageBox(0,L"Hey there again!",0,0);
}
when you call RunDll32 with parameter mydllmain, it does me give both the message box with out error.
There's no reason to call DllMain via RunDLL, it's called automatically when the DLL is loaded.
Rather try running a custom function.
Aside from that, the problem is probably the exported name. You need to write a .def file for the DLL.
DllMain it is caused automatically, always. it to cause through rundll32, it will be caused, for this purpose it and is "entry point", you repeatedly try to cause it.
I have created a global Keyboard hook.
Hook is created in a DLL.
#pragma comment(linker, "/SECTION:.SHARED,RWS")
#pragma data_seg(".SHARED")
static HHOOK hkb=NULL;
static CMyFile *pLF;
#pragma data_seg()
HINSTANCE hins = NULL;
extern "C"
LRESULT __declspec(dllexport) __stdcall CALLBACK KeyBoardHookProc(
int nCode,
WPARAM wParam,
LPARAM lParam)
{
if (nCode < 0) {
return CallNextHookEx(0, nCode, wParam, lParam);
}
return CallNextHookEx(hkb, nCode, wParam, lParam);
}
extern "C"
LRESULT __declspec(dllexport) __stdcall CALLBACK Install()
{
pLF = new CMyFile(L"c:\\1.txt");
hkb = SetWindowsHookEx(WH_KEYBOARD,(HOOKPROC)KeyBoardHookProc,hins,0);
return 0;
}
extern "C"
BOOL __declspec(dllexport) __stdcall CALLBACK UnInstall()
{
return UnhookWindowsHookEx(hkb);
}
BOOL APIENTRY DllMain( HMODULE hModule,
DWORD ul_reason_for_call,
LPVOID lpReserved
)
{
switch(ul_reason_for_call)
{
case DLL_PROCESS_ATTACH :
hins = (HINSTANCE) hModule;
break;
case DLL_THREAD_ATTACH :
break;
case DLL_THREAD_DETACH :
break;
case DLL_PROCESS_DETACH :
break;
}
return TRUE;
}
I have craeted one EXe that loads this dll and calls install function of the hook dll.
HMODULE hMod = LoadLibrary(L"hk.dll");
if(hMod!=NULL)
{
typedef LRESULT (__stdcall CALLBACK *_installhk)() ;
_installhk installProc;
installProc = (_installhk) GetProcAddress(hMod,"Install");
if(installProc!=NULL)
{
installProc();
}
}
While debugging breakpoint on KeyBoardHookProc is being hit only once when I launch the exe.
The exe keeps on running unless I close it but if I enter anything else from keyboard the hook procedure not getting called.
What could be the reason for this?
Is this not the right way to setup global keyboard hook?
How did you test that the hook procedure is not called ? If you tried to check it with a breakpoint, you have to take care that your hook dll is loaded in every process but your breakpoint is only put in your current process.
If you have any window in your application, focus on it before hitting keys or debug it using logs.
Another solution is to hook with WH_KEYBOARD_LL which does not require an extra DLL. You can hook directly from your process.
Have a look at the late Paul DiLascia's code which installs a global keyboard hook to trap the Ctrl+Alt+Del, Task Manager. MSDN September 2002 'Disabling keys in XP with TrapKeys'
Hope this helps,
Best regards,
Tom.
This may not be directly related to your main problem, but your use of the CMyFile object has several issues:
The CMyFile object is allocated dynamically using new CMyFile(...). This will create it only in the memory space of one process.
The pLF pointer is uninitialized. This means it will be placed in the BSS segment instead of the shared data segment. To fix this, declare it with CMyFile *pLF = NULL;.
CMyFile itself probably has members containing file handles and/or pointers which won't work properly in other processes.
Regarding your main question:
You seem to be creating the hook correctly as far as I can see.
There is no need to cast to HOOKPROC in the call to SetWindowsHookEx. If you get a warning without it, there is a problem with your function type.
There's no need for the if statement in the hook proc - the first parameter to CallNextHookEx is ignored anyway on modern Windows, so both branches effectively do the same thing.
I don't know if I'd trust debugger breakpoints on a hook procedure called from different processes - it's possible that the procedure is called but the debugger isn't catching it.
extern "C" is good it will get rid of the name mangling mentioned above but __stdcall will conflict with this.
You should use the RegisterHoyKey API call instead - it's much less hassle (as I found out myself recently when I replaced a similar keyboard hook DLL!).
Check your export section for DLL and see what name linker exported your "Install" function. C++ mangles with export function names. I bet you anything it is not "Install" but rather _Install#12 or something like that.
If I have a dll called "foo.dll" and the end user renames it to "bar.dll". After calling to a LoadLibrary, how can I get the name "bar.dll" from inside my dll?
Is it GetModuleFileName(hModule, buffer); ?
yes, you need to store hModule in DllMain
BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved)
{
switch (fdwReason)
{
case DLL_PROCESS_ATTACH:
hModule = hinstDLL;
break;
}
}
You need to provide DllMain function, store the module handle you get passed in a static variable, and then use that variable to call GetModuleFilename. You should avoid calling GetModuleFilename (or any other function) in DllMain itself, as Windows is very picky about what you can and can't do in there.