Thread: Empty WH_CALLWNDPROC hook crashes program right after WM_WINDOWPOSCHANGING message

Hi,

I'm trying to hook into firefox.exe to capture a few messages. Which seems to work fine (messages are received), however when I give the window focus (by clicking on it in the task bar) Firefox crashes. It always happens right after the hook receives the WM_WINDOWPOSCHANGING message.

My DLL code is:

Code:

FIREFOXDLL_API LRESULT GetMsgProc(
  int code,
  WPARAM wParam,
  LPARAM lParam
)
{
  return CallNextHookEx(0, code, wParam, lParam);
}

I've previously had some file writing code here, to output the message data, which is how I know it always crashes after the WM_WINDOWPOSCHANGING message.

The main program has the following function:

Code:

// Called using EnumWindows(enumMainWindows, processID);
// hkprcSysMsg and hinstDLL are correctly initialized
BOOL CALLBACK enumMainWindows(HWND hwnd, LPARAM lParam)
{
  DWORD pid;
  GetWindowThreadProcessId(hwnd, &pid);
  if (pid == lParam)
  {
    DWORD tid = GetWindowThreadProcessId(hwnd, NULL);
    SetWindowsHookEx( 
                          WH_CALLWNDPROC,
                          hkprcSysMsg,
                          hinstDLL,
                          tid); 
    return false;
  }
  return true;
}

If anyone could share any insight they might have regarding what can be causing this, it would be much appreciated.