LeakMon :- Part 2 Under the hood

This post explains how LeakMon application tracks various kind of resource allocation and report them.

Download Source :- LeakMon_source.zip

Basic working principle

Consider the case of tracking memory allocation. In this case, Leakmon will hook all the possible memory allocation and de-allocation functions. So when ever a function allocates some memory it will keep the pointer to the newly allocated memory as a key in a map and the call stack as value. If this memory is de-allocated, this entry in the map is removed. So at any point all the entries in the map are those memory pointers which haven't de-allocted. When you ask the Leakmon to Dump the leak, all it does is dumping the entries in the map.

This application has the following distinguishing features from the other resource leak tracking applications in codeproject and around.

1. You dont have to modify any single line of code to start tracking

2. It will track the allocation from all the binaries in the process. Means the tracking is not restricted to only the EXE binary of the process. It will track allocation from all the dependent DLL's as well

OK, Let's start with the working of LeakMon from the first binary, Injector.exe

Injector application



The Injector.exe allows you to select the process of which you want to track leak. It will list all the process in the system with the help of CreateToolhelp32Snapshot, Process32First and Process32Next functions.

So, when if you select a process and press the "Inject" button, what it does is, It will inject the "HookDll.dll" to the traget process' address space. This is done with the help of CreateRemoteThread API. Injecting a DLL using CreateRemoteThread API is explained detailed in the article Three Ways to Inject Your Code into Another Process. Anyway in Injector.exe the following code part does the injection.

void CInjectorDlg::OnInject()
{
......
CString csPid = m_List.GetItemText( nSelected, 0 );
DWORD dwPID = _ttoi( csPid );
HANDLE hProcess = OpenProcess( PROCESS_CREATE_THREAD|PROCESS_QUERY_INFORMATION|
PROCESS_VM_OPERATION|PROCESS_VM_WRITE|PROCESS_VM_READ,
FALSE, dwPID );
if( !hProcess)
{
      AfxMessageBox( _T("Failed to open the process" ));
      return;
}
HINSTANCE hLib = LoadLibrary( "Kernel32.dll" );
PROC pLoadLib = (PROC)GetProcAddress( hLib, "LoadLibraryA" );
void* pLibRemote = ::VirtualAllocEx( hProcess, NULL, csPath.GetLength(),
MEM_COMMIT, PAGE_READWRITE );
::WriteProcessMemory( hProcess, pLibRemote, (void*)csPath.operator LPCTSTR(),
csPath.GetLength(), NULL );
if( !CreateRemoteThread( hProcess, 0, 0, (LPTHREAD_START_ROUTINE)pLoadLib, pLibRemote, 0, 0 ))
{
          AfxMessageBox( "Create Remote thread Failed" );
          :VirtualFreeEx( hProcess, pLibRemote,csPath.GetLength(), MEM_RELEASE );
}
}

The HookDll

HookDll.dll is the core part of the LeakMon. It performs almost all of the resource tracking stuffs. HookDll starts its working once it got injected into the target process. The BOOL CHookDllApp::InitInstance function gets called when this dll is loaded in the target process. This function however doesn't do much other than just creating a worker thread, DumpController.

BOOL CHookDllApp::InitInstance()
{
       HANDLE hThread = ::CreateThread( 0,0,DumpController, 0,0, 0 );
      CloseHandle( hThread );
      return CWinApp::InitInstance();
}

Now when the DumpController starts, it will first show the configuration dialog, where you can,
1. Select what kind of resource allocation you want to track
2. Select the path of the PDB's of the application
3. Stack depth

DebugHelp Functions

HookDll creates the call the stack, with the help of DebugHelp Functions. For the DebugHelp function to return the call stack correctly, it is necessary that you specify the correct PDB path of the application. Also it always good to use the latest version of the dbghelp.dll that comes with latest version of Debugging tool for windows. Another good feature that LeakMon support is integration with symbol server. However, adding the Symbol server functionality is very easy. All you have to do is to ensure that, the symsrv.dll is present in the same directory from where dbghelp.dll is loaded.

So now once you click the OK button, in the config dialog, the HookDll will start initializing symbol handler. To initialize symbol handler we have to call SymInitialize. When you call SymInitialize with the value of fInvadeProcess as TRUE, it will load symbol table for all the dlls in the process. But wait, we do better, we can show the progress of loading the symbols of each dll. Showing the progress of symbol loading is important especially when you are downloading a symbol from symbol server, which may take significant time.You might have seen this feature in Visual studio. when you start debugging an application in VS, it will show the symbol loading progress of each dll in the status bar.

To show the progress, we can register one call back with the function SymRegisterCallback64. Our callback function will get called before loading each symbol.

void ConfigDlg::OnOk()
{
..................
       SymInitialize(GetCurrentProcess(), (LPTSTR)csWholePath.operator LPCTSTR() , FALSE );
       SymRegisterCallback64( GetCurrentProcess(),SymRegisterCallbackProc64,(ULONG64 )this );
..................
       if( pSymRefreshModuleList )
       {
              pSymRefreshModuleList( GetCurrentProcess());
       }
       ..................
}


BOOL CALLBACK ConfigDlg::SymRegisterCallbackProc64(HANDLE hProcess,
                                                                                                ULONG ActionCode,
                                                                                                ULONG64 CallbackData,
                                                                                                ULONG64 UserContext)
{
       if( CBA_DEFERRED_SYMBOL_LOAD_START == ActionCode )
       {
              PIMAGEHLP_DEFERRED_SYMBOL_LOAD64 pSybolLoadInfo =(PIMAGEHLP_DEFERRED_SYMBOL_LOAD64)CallbackData;
              ConfigDlg* pDlg = (ConfigDlg*)UserContext;
              CString csLoadtext = _T("Loading symbol for file: ");
              csLoadtext += pSybolLoadInfo->FileName;
              pDlg->m_ProgressDlg.SetDlgItemText( IDC_LOAD_INFO, csLoadtext );
       }
       // return false to indicate that we are not doing any symbol loading by ourself
       return FALSE;
}

API Hooking

To intercept the allocation and de-allocation calls(functions) made by dll's, LeakMon relies on User mode API hooking though IAT patching. I am not going to explain the IAT patching because there are already several articles in codeproject and other sites having a detailed explanation. Here is one good article to start with API hooking revealed.

How ever one thing that is different in LeakMon with usual custom is that, it doesn't walk through the dependency chain of dll. I mean, if A.exe has statically linked to B.dll and again if B.dll is linked to C.dll, what usually does for API hooking is, it will hook the API imported by A.exe, then find out the dependency of A.exe, which is B.dll, so hook its imported functions. Then it find out the depended dll of B.dll which is C.dll, hook it functions and so on. The problem with this approach is that only statically linked dlls will be hooked. If you are making some calls to a COM dll or if I you are creating an Active-X control in your application, those dll will never get hooked. So instead of walking through the dependency chain, Leakmon, enumerates all the dll's in that process and hooks it. In fact this approach is a little more easier too. It make use of the Module32First and Module32Next set of functions for this purpose.

As you can see, this application can track three kind of resource allocation and de-allocation namely Memory, GDI objects and HANDLES. Windows have a wider set of function for allocation and de-allocation for each of of resources. The following table shows the list of API's LeakMon hooks for tracking allocations/de-allocation of resources.

Memory allocation and de-allocation functions
HeapAlloc	HeapFree	HeapReAlloc	VirtualAllocEx
VirtualFreeEx	GlobalAlloc	GlobalReAlloc	GlobalFree
LocalAlloc	LocalReAlloc	LocalFree

GDI object creation and deletion functions
Bitmaps
LoadBitmapA	LoadBitmapW	LoadImageA
LoadImageW	CreateBitmap	CreateBitmapIndirect
CreateCompatibleBitmap	CreateDIBitmap	CreateDIBSection
CreateDiscardableBitmap	CopyImage	GetIconInfo
GetIconInfoExA	GetIconInfoExW
Icons
CopyIcon	CreateIcon	CreateIconFromResource
CreateIconFromResourceEx	CreateIconIndirect	DestroyIcon
DuplicateIcon	ExtractAssociatedIconA	ExtractAssociatedIconW
ExtractAssociatedIconExA	ExtractAssociatedIconExW	ExtractIconA
ExtractIconW	ExtractIconExA	ExtractIconExW
LoadIconA	LoadIconW	PrivateExtractIconsA
PrivateExtractIconsW
Cursor
CreateCursor	DestroyCursor	LoadCursorA
LoadCursorW	LoadCursorFromFileA	LoadCursorFromFileW
Brush
CreateBrushIndirect	CreateSolidBrush	CreatePatternBrush
CreateDIBPatternBrush	CreateDIBPatternBrushPt	CreateHatchBrush
Device context
CreateCompatibleDC	CreateDCA	CreateDCW
CreateICA	CreateICW	GetDC
GetDCEx	GetWindowDC	ReleaseDC
DeleteDC
Font
CreateFontA	CreateFontW	CreateFontIndirectA
CreateFontIndirectW
Metafile
CreateMetaFileA	CreateMetaFileW	CreateEnhMetaFileA
CreateEnhMetaFileW	GetEnhMetaFileA	GetEnhMetaFileW
GetMetaFileA	GetMetaFileW	DeleteMetaFile
DeleteEnhMetaFile	CopyEnhMetaFileA	CopyEnhMetaFileW
CloseEnhMetaFile	CloseMetaFile
Pen
CreatePen	CreatePenIndirect	ExtCreatePen
Region
PathToRegion	CreateEllipticRgn	CreateEllipticRgnIndirect
CreatePolygonRgn	CreatePolyPolygonRgn	CreateRectRgn
CreateRectRgnIndirect	CreateRoundRectRgn	ExtCreateRegion
Palette
CreateHalftonePalette	CreatePalette
Common Function
DeleteObject

Handle creation and deletion functions
Synchronization objects
CreateEventA	CreateEventW	CreateEventExA
CreateEventExW	OpenEventA	OpenEventW
CreateMutexA	CreateMutexW	CreateMutexExA
CreateMutexExW	OpenMutexA	OpenMutexW
CreateSemaphoreA	CreateSemaphoreW	CreateSemaphoreExA
CreateSemaphoreExW	OpenSemaphoreA	OpenSemaphoreW
CreateWaitableTimerA	CreateWaitableTimerW	CreateWaitableTimerExA
CreateWaitableTimerExW	OpenWaitableTimerA	OpenWaitableTimerW
File function
CreateFileA	CreateFileW	CreateFileTransactedA
CreateFileTransactedW	FindFirstFileA	FindFirstFileW
FindFirstFileExA	FindFirstFileExW	FindFirstFileNameTransactedW
FindFirstFileNameW	FindFirstFileTransactedA	FindFirstFileTransactedW
FindFirstStreamTransactedW	FindFirstStreamW	FindClose
OpenFileById	ReOpenFile	CreateIoCompletionPort
Authorization function
CreateRestrictedToken	DuplicateToken	DuplicateTokenEx
OpenProcessToken	OpenThreadToken
Directory management
FindFirstChangeNotificationA	FindFirstChangeNotificationW	FindCloseChangeNotification
File mapping
CreateMemoryResourceNotification	CreateFileMappingA	CreateFileMappingW
CreateFileMappingNumaA	CreateFileMappingNumaW	OpenFileMappingA
OpenFileMappingW
Memory
HeapCreate	HeapDestroy	GlobalAlloc
GlobalReAlloc	GlobalFree	LocalAlloc
LocalReAlloc	LocalFree
Process and thread
CreateProcessA	CreateProcessW	CreateProcessAsUserA
CreateProcessAsUserW	CreateProcessWithLogonW	CreateProcessWithTokenW
OpenProcess	CreateThread	CreateRemoteThread
OpenThread	CreateJobObjectA	CreateJobObjectW
Mail slot
CreateMailslotA	CreateMailslotW
pipe
CreatePipe	CreateNamedPipeA	CreateNamedPipeW
Registry
RegCreateKeyExA	RegCreateKeyExW	RegCreateKeyTransactedA
RegCreateKeyTransactedW	RegOpenCurrentUser	RegOpenKeyA
RegOpenKeyW	RegOpenKeyExA	RegOpenKeyExW
RegOpenKeyTransactedA	RegOpenKeyTransactedW	RegOpenUserClassesRoot
RegCreateKeyA	RegCreateKeyW	RegCloseKey
Common functions
DuplicateHandle	CloseHandle

Note:- I have tried my best to include all the functions I know which allocates or de-allocate resources. Still, if know some function that i have missed, please let me know.

Now lets see how the hooking works. For each of the function in the above table LeakMon have a dummy function ( Which is actually 199 dummy functions ). So after hooking, the application will be calling my dummy function instead of the original function. In the dummy function what it does is,

1) Call the original function

2) Create the call stack and store it

3) Return the return value of retured by original function

Let's check the example of HeapAlloc function ( Remember that all the memory allocation functions such as new, malloc etc will finally ends up in calling HeapAlloc function to allocate memory. Similarly free, delete functions calls HeapFree ).

LPVOID WINAPI MyHeapAlloc( HANDLE hHeap,
                                                         DWORD dwFlags,
                                                         SIZE_T dwBytes )
{
           LPVOID lMem = pOrgHeapAlloc( hHeap, dwFlags, dwBytes );
           CreateCallStack( lMem, dwBytes );
           return lMem;
}

The CreateCallStack function creates the current function call stack and save it in a map. The key of the map is the memory address returned by original HeapAlloc and value is a structure which holds the call stack and size of memory allocated.

Now when the application calls HeapFree, the dummy function just removes the entry from the map and then call the original HeapFree function.

BOOL WINAPI MyHeapFree( HANDLE hHeap, DWORD dwFlags, LPVOID lpMem )
{
       RemovCallStack( lpMem );
       return pOrgHeapFree( hHeap, dwFlags, lpMem );
}

Creating the Call Stack

This is the only part which actually has different processing for 64 bit and 32 bit. In 32 bit applications the call stack is created using the StackWalk64 function. You can either check the code ( StackDump function ) or read this nice article Walking the callstack, to learn more about the StackWalk64 function.

The stack walking in x64 machine was bit difficult for me. I actually had no idea how to do it. Thanks to Ken Johnson for posting an example of stack walking in x64 machine which practically made me to port this application to 64 bit also.

Dumping the leaks

After the hook dll have setup all the hooks, it will wait for couple of events. One among those event is Dump event. When user clicks on the Dump button in the Injector application, it will set the dump event to signalled state. When this event is signalled the thread in the HookDll will start dumping each entry in the map to a user specified file. The format of the dumpfile is mentioned in the previous post.

That's all the main thing about the Injector and HookDll. There is one more application DumpViewer, which actually has some nice features done using Visual Studio automation. I will explain those things in another post.

Open Source

I got couple of request to make this project open source, so I have opened a project in code.google.com and is available at http://code.google.com/p/leakmon/ . So if you have some idea or got some improvement points you are welcome to join me there. Suggestions are also welcome.

LeakMon - Track Handle leak, GDI leak and Memory leak in your applications

LeakMon is a light weight resource leak tracking utility which can track Memory leaks, GDI object leaks and handle leaks of a process. This tool is suitable mainly for tracking down the leaks that happens in between an operation.

Downloads
LeakMon

[Download from Codeproject]
LeakMon

Prerequisite

• You need to have installed VS2010 or Microsoft Visual C++ 2010 Redistributable Package.

Visual C++ 2010 Redistributable Package can be downloaded from the below path

For 32 bit applications (4.8 MB)

http://www.microsoft.com/downloads/en/details.aspx?familyid=A7B7A05E-6DE6-4D3A-A423-37BF0912DB84&displaylang=en

For 64 bit application (5.5 MB)
http://www.microsoft.com/downloads/en/details.aspx?familyid=BD512D9E-43C8-4655-81BF-9350143D5867&displaylang=en

How to use

This tool consists of three binaries, Injector, HookDll and a DumpViewer.
To start with, run the Injector.exe.



• Refresh :- Refresh the process list
• Inject :- Injects the hook DLL to the target process to start tracking of the leak
• Dump : - Dumps the leak found so far to a file.
• Reset: :- Ignore/Clear all the leaks found up to this point.
• PDB Info : - After Injecting the DLL to the target process, you can click this button to view and make sure that all the pdb’s of necessary DLL’s are loaded correctly.

Using the injector.exe, select the target process that you want to debug. In this case say "MultiThread.exe". Now to start tracking, click the “Inject” button. On doing this, a settings window as in the below figure will pop up. (Note: The settings window is actually shown in the target process' context).

The setting window allows you to choose the “type of leak” you want to track. The types include memory leak, GDI leak and Handle leak.

The next option in the Settings dialog is “Stack Depth”. The value in the stack depth controls the number of functions that will be retrieved while tracking the allocation call stack. The value you enter in here can considerably affect the speed of the application. Lesser the value, the faster the application will be.

Collecting the call stack will never be perfect, without proper PDB files. So to get proper call stack information, specify the path PDB files of the binaries used in your application. Without the pdb’s of Microsoft dll’s such as MSVCRT.dll, MFCxx.dll etc, you will not be able to see the call stack of memory allocated using new and new[] sometimes. If you don’t have the symbols for Microsoft dlls, click on the “Add Symbol server”. Also it is a must that you have to specify the Folder in which the LeakMon binary resides. (“T:\LeakMon” in the below sample). Once you have set all the necessary pdb’s path click OK. The tracking starts from this moment

So now, once you have finished your processing and want to see all the allocations that haven’t de-allocated, press the “Dump” button in the injector. If there is some leak, it will prompt you with a save dialog, though which you can save the leak information file.

Analyzing the leak dump file


I will explain the format of the dump file with the following example. Consider the below code

i.e. The sequence of calling is in the order


CMulitThreadDlg::OnBnClickedButton1()->func1()->func2().

Now the information regarding the memory leak in the above code will look as follows.

-->Bytes allocated -- 76

_heap_alloc_base f:\dd\vctools\crt_bld\self_x86\crt\src\malloc.c(105)
_heap_alloc_dbg_impl f:\dd\vctools\crt_bld\self_x86\crt\src\dbgheap.c(427)
_nh_malloc_dbg_impl f:\dd\vctools\crt_bld\self_x86\crt\src\dbgheap.c(239)
_nh_malloc_dbg f:\dd\vctools\crt_bld\self_x86\crt\src\dbgheap.c(296)
_malloc_dbg f:\dd\vctools\crt_bld\self_x86\crt\src\dbgheap.c(160)
operator new f:\dd\vctools\vc7libs\ship\atlmfc\src\mfc\afxmem.cpp(407)
operator new[] f:\dd\vctools\vc7libs\ship\atlmfc\src\mfc\afxmem.cpp(442)
operator new[] f:\dd\vctools\vc7libs\ship\atlmfc\src\mfc\afxmem.cpp(67)
func2 t:\naveen\pgms\cpp\2008\mulitthread\mulitthreaddlg.cpp(178)
func1 t:\naveen\pgms\cpp\2008\mulitthread\mulitthreaddlg.cpp(184)
CMulitThreadDlg::OnBnClickedButton1 t:\naveen\pgms\cpp\2008\mulitthread\mulitthreaddlg.cpp(189)
_AfxDispatchCmdMsg f:\dd\vctools\vc7libs\ship\atlmfc\src\mfc\cmdtarg.cpp(82)
CCmdTarget::OnCmdMsg f:\dd\vctools\vc7libs\ship\atlmfc\src\mfc\cmdtarg.cpp(381)
CDialog::OnCmdMsg f:\dd\vctools\vc7libs\ship\atlmfc\src\mfc\dlgcore.cpp(85)
CWnd::OnCommand f:\dd\vctools\vc7libs\ship\atlmfc\src\mfc\wincore.cpp(2364)
CWnd::OnWndMsg f:\dd\vctools\vc7libs\ship\atlmfc\src\mfc\wincore.cpp(1769)
CWnd::WindowProc f:\dd\vctools\vc7libs\ship\atlmfc\src\mfc\wincore.cpp(1755)

Starting from the top function, traverse down, until you find a function from your file. In the above case, func2().  So it can be concluded that, some memory that has allocated from the func2() haven’t de-allocated.

Analyzing the leak with DumpViewer

Even though you can viewer the dump file in any text editor, DumpViewer provides you some extra features that are really handy. Most of the features are self explanatory. One of the main feature is that, when you double click on a particular function in the tree, it will open the source file in visual studio with the line in which leak occurred as selected.

Under the Hood

This application basically works by hooking all the possible functions that allocates and de allocates a resource. For example when tracking memory leak it hooks the memory allocation API's such as HeapAlloc, HeapFree, VirtualAlloc, VirtualFree etc. A more detailed step by step explanation of this tool will be posted in next posts.

I have tried my best to remove the bugs in this application. But still if you encounter any bugs, let me know. Suggestions or improvements are highly appreciated.

[Update] :- Part 2  Leakmon- Under the hood

Dependency Checker

This is a simple light weight utility to find which all dll/exe/ocx in a folder uses a particular dll.

Download
Source File(DependsChecker_Src.zip)
Execuatble(DependsChecker_bin.zip)

My development environment usually includes large number of binaries. And I was working in some core library module which is used by many other dlls. So whenever I change something in the header file of this code library, I have to rebuild all the dependent libraries. Rebuilding the entire environment was not practical all times. So I had to create such an utility so that I can find out who all uses this code library and can rebuild those modules only.

How to Use

1. In the “Dll Name” edit box, enter the name of the dll for which we have to search for.
2. In the “Path” edit box, enter the folder in which we have to search for dlls/exe/ocx that uses dll entered in the “Dll Name” edit box.
3. Click “Start” button.

Upon clicking the Start button, the list control starts’ populating the Dll, OCX and EXE’s that uses the specified dll. Please note that this application will not list dynamic dependencies and so we cannot enter ocx or COM dll as “Dll Name”.

How it works

When the start button is clicked, the application loop through each Dll, OCX and EXE’s in the specified folder. It opens each binary, parse the PE (Portable Executable) file format.
For example consider that user32.dll is specified in the "Dll name" edit box and the path is "c:\windows\system32". When user clicks on the “start” button, the application took a loop to find EXEs, dll's and OCXs in the specified folder. Intitally it enumarets all the EXEs. Suppose we got "calc.exe" as file name. The next thing to do is to map the binary file to memory. This is performed with the help of CreateFileMapping() and MapViewOfFile() function.

CFile fl;
if( !fl.Open( csExeName, CFile::modeReadCFile::shareDenyNone, 0 ))
{
CString csMsg;
csMsg.Format( _T(" Failed to open file %s"), csExeName );
AfxMessageBox( csMsg );
continue;
}
HANDLE hSM = CreateFileMapping( (HANDLE)fl.m_hFile, 0,PAGE_READONLY,0,0, _T("some_sM"));
LPVOID pBinary = MapViewOfFile( hSM,FILE_MAP_READ,0,0, fl.GetLength());
if( CheckForDependecy( csDllName, pBinary ))
{
m_List.InsertItem( 0, fl.GetFileName() );
}
UnmapViewOfFile( pBinary );
CloseHandle( hSM );
fl.Close();

As you can see in the above code, after the binary is loaded to the memory, the memory address is passed to the CheckForDependecy() function. The function cast the memory address to a IMAGE_DOS_HEADER pointer.

PIMAGE_DOS_HEADER pDOSHeader = (PIMAGE_DOS_HEADER) lpStartAddress;

After this, it will try to get the IMAGE_NT_HEADERS from pDOSHeader. Usually the 16 bit binaries will not be having this header. So we will ignore such binaries at this point.

// Get the PE header.
PIMAGE_NT_HEADERS pNTHeader = MakePtr(PIMAGE_NT_HEADERS, pDOSHeader, pDOSHeader->e_lfanew);
if( IsBadReadPtr( pNTHeader, sizeof( IMAGE_NT_HEADERS)))
{
return false;
};

May be because of the property of data in the file, it may occur that the pNTHeader points to a valid memory. So we will add one more checking to confirm that we are dealing with PE file (The famous DRWATSON.EXE fails at this checking!!!ya it is not a PE file).

char* pSig = (char*)&pNTHeader->Signature;
if( pSig[0] != 'P' pSig[1] != 'E')
{
return false;
}

The next task is to find the IMAGE_IMPORT_DESCRIPTOR. The IMAGE_NT_HEADERS.OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_IMPORT]. VirtualAddress holds the relative address of IMAGE_IMPORT_DESCRIPTOR from the starting of the memory. We can use the ImageRvaToVa() API to convert the relative adress to virtual address. There's one IMAGE_IMPORT_DESCRIPTOR for each imported executable. So we will loop through each item and check whether it is for importing the specified dll (“user32.dll” in our case )

PIMAGE_IMPORT_DESCRIPTOR pImportDesc = (PIMAGE_IMPORT_DESCRIPTOR) ImageRvaToVa( pNTHeader, lpStartAddress, pNTHeader->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_IMPORT].
VirtualAddress, 0 );
while( pImportDesc && pImportDesc->Name )
{
// pImportDesc->Name holds the name of the import library
PVOID pName = ImageRvaToVa( pNTHeader, lpStartAddress, pImportDesc->Name , 0 );
PSTR szCurrMod = (PSTR)pName;
if( IsBadReadPtr( szCurrMod, 1 ))
{
continue;
}
CString cs = szCurrMod;
if( 0 == cs.CollateNoCase( csDllName ))
{
// everything pass. We have found one dependency
return true;
}
// Move to the next import library
pImportDesc++;
}

And for the records, let me say that, there are 1111 files in my system32 folder that has dependency with the user32.dll( Vista SP1 ).

Centralizing modeless child dialog

Normally when we call the DoModal() function of a dialog, the dialog will created and displayed at the center of the parent dialog.



But when a modless dialog is displayed, the child dialog will be displayed at the top left portion of the parent dialog.



I noticed this when a codeproject user asked how to centralize a modeless child dialog. Initially I thought that MFC might be doing some thing in the DoModal() function. So I stepped into the DoModal() function. But I couldn't find any difference in the dialog creation in CDialog::DoModal and CDialog::Create().
Another difference that I know between a modal and modeless dialog is that, in the case of the modal dialog, the parent window will be disabled. MFC does this inside the DoModal() function. To try my luck I disabled the parent window before calling the Create function of dialog. Surprisingly it worked! The modeless child dialog came at the center of parent dialog.

So if you want to centralize a modeless dialog, just disable the parent dialog before create and re-enable it after the creation.

void CDialogBased2Dlg::OnBnClickedButton1()
{
    EnableWindow( FALSE );
    m_ChildDlg.Create( ChildDialog::IDD, this );
    EnableWindow( TRUE );
    m_ChildDlg.ShowWindow( SW_SHOW );
}

Function to get the local system Administrator Name

A codeproject poster asked this question. He was already aware of the NetLocalGroupGetMembers function with which, was can the list of users in any groups in the system. How were he wasn't quite sure how to use it and there wasn't any sample code in the internet. So I wrote a sample and posted in codeproject and here is the copy of it.

LPLOCALGROUP_MEMBERS_INFO_1  pstMembersInfo = 0;
DWORD entriesread = 0;
DWORD totalentries = 0;
if( 0 != NetLocalGroupGetMembers( NULL, _T("Administrators"), 1, (LPBYTE*)
                                  &pstMembersInfo,MAX_PREFERRED_LENGTH,
                                  &entriesread, &totalentries, 0 ))
{
      AfxMessageBox( _T("NetLocalGroupGetMembers failed !"));
      return ;
}
for( DWORD dwIdx =0; dwIdx  < entriesread; dwIdx ++ )
{
     AfxMessageBox( pstMembersInfo[dwIdx].lgrmi1_name );
}
NetApiBufferFree( pstMembersInfo );

How to find whether the parent process is GUI or Console

This is not 100% fool proof. How ever in normal cases, this works great. This technique can be used to find out, whether the child application was launched from a GUI application or from a Console application.

if( AttachConsole( ATTACH_PARENT_PROCESS ))
{
     AfxMessageBox( _T("Parent process is a console application"));
}
else
{
     AfxMessageBox( _T("Parent process is not a console application"));
}

new with empty bracket

Have you ever wrote a statement like..

int *pnValue = new int[];

One of my friend asked me what will happen if the above statement is executed. Executed ??? I though the code won't even compile. Surprisingly it compile and even returned a pointer. Wow that was some thing unbelievable.

OK now the question is, what will be size of memory that pnValue points?

The two API's in windows that allocates and de allocates the memeory are HeapAlloc and HeepFree. The CRT functions malloc and free are actually wrappers the above API. The new, new[], delete, delete[] are again another wrapper around the malloc and free. So when ever you allocates some memory using new or new[], it will finally reach the HeapAlloc function. This function is defined as

LPVOID WINAPI HeapAlloc(
__in HANDLE hHeap,
__in DWORD dwFlags,
__in SIZE_T dwBytes
);

From the above definition, you can see that the third parameter to this function is the number of BYTES to be allocated . So to find out what "new int[]" returns, we can put a break point in the entry point of HeapAlloc and check the value of dwBytes( in dis assembly ).

when I tried, the dwBytes turned out be 1 !!! This one byte cannot even hold one int variable. That means any further operation using such a pointer will possibly crash.

Another interesting thing is "int *pnValue = new int[0];" also returns a pointer pointing a memory of 1 byte long.