C / C++ / MFC

15-Apr-20 12:21

VS2008, Windows Embedded Compact 7, mfc dialog application that is 4 years old. It's been working fine. Today I've been making improvements, tracking down some long standing issues. Up until this afternoon, I could pretty much debug where I wanted but then suddenly my UI loop stalled in the OnInitDialog. Stepping through, I came to a couple of LoadBitmap calls that I use to load images from the embedded resources. The first call does not error out, it just never comes back from the LoadBitmap call.

This smells like some weird elephanting debris from VS2008. Some references suggest memory issues on the target device, etc, but it's been rebooted, this is a lightweight app... and doesn't use much memory.

Anyone seen LoadBitmap stall like this?

Charlie Gilley
<italic>Stuck in a dysfunctional matrix from which I must escape...

"Where liberty dwells, there is my country." B. Franklin, 1783
“They who can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.” BF, 1759

_Flaviu16-Apr-20 1:37

16-Apr-20 1:37

Did you tried to load another bitmap, something small in order to find out where is the problem ?

charlieg16-Apr-20 4:30

16-Apr-20 4:30

I actually did... there are only three bitmaps in the project. I added some code:

C++

CBitmap myBitmap;
myBitmap.LoadBitmap(IDB_STOP);

it never returns from the LoadBitmap... very odd. The bitmaps are not large (200x200?), and the really weird part, again, is that this code has been working for many years.

_Flaviu16-Apr-20 5:24

16-Apr-20 5:24

I would try a little workaround: use CImage instead of CBitmap ... at least you will know where is the problem, or, you will solve the issue .... However, CBitmap is reliable ... I don't think that code from above is causing the problem ... the cause must be in else where.

leon de boer16-Apr-20 6:29

16-Apr-20 6:29

Check you have not got a clash on IDB_STOP and you actually have the resource of that ID in the project. All you need is a corrupt resource file and it can't connect the dots.

In vino veritas

_Flaviu16-Apr-20 7:21

16-Apr-20 7:21

That's why I told him to try to load another bitmap resource Smile | :)

just for testing ...

charlieg16-Apr-20 9:47

16-Apr-20 9:47

good idea, "use the source luke"... looking now - yeah, this looks good. I would expect the loadbitmap operation would just fail and not hang. The resource is built into the exe. Trying the load image... I love you Microsoft.

charlieg16-Apr-20 10:27

16-Apr-20 10:27

So, tried the CImage -> LoadImage approach - no go. Hangs in that call as well. I'm going to sell my house and buy a sailboat....

elephanting code - okay, I figured out why the call hangs. This application is my application loader code in an embedded target. We have two types of upgrades - one with and one without an operating system. So, one thing I need to do is dismount and remount the device partitions (this is Windows Embedded Compact 7), so I can modify OS files. This typically is not a concern, since by the time we're running, everything is running out of ram. Once complete, the device reboots. No harm.

Now I don't know how LoadBitmap is implemented, but it appears that it reads the resource information from the exe file and not what is in RAM. Egg on my face since I missed the #define change. I still argue that LoadBitmap should return gracefully with an error code. Heh it's mfc, filed under "don't do that."

Appreciate all the suggestions.

leon de boer16-Apr-20 16:37

16-Apr-20 16:37

I agree LoadBitmap should not fail like that but it is specified the resources are never lifted into RAM. They are tagged in special sections in the file and are excluded from the normal executable load to avoid using memory when not required. Remember a file may contain many resources for different resolutions, languages and the like and much would then be redundant duplicates hogging memory.

In vino veritas

charlieg17-Apr-20 9:43

17-Apr-20 9:43

Windows CBT Hooks

Richard Andrew x6414-Apr-20 11:58

14-Apr-20 11:58

After I install a CBT global hook, does the application that called SetWindowsHookEx[^] need to stay alive for the hook to work for the lifetime of the user session?

Or may the application that installed the hook exit, thus leaving the hook DLL to operate by itself?

The difficult we do right away...
...the impossible takes slightly longer.

Richard MacCutchan14-Apr-20 21:21

14-Apr-20 21:21

The remarks section certainly implies quite strongly that the application that calls SetWindowsHookEx must keep running (and pumping messages).

Richard Andrew x6415-Apr-20 4:28

15-Apr-20 4:28

Thank you Richard. I reread the remarks and I see that you are correct.

Quote:
However, because a 32-bit application must run the hook code, the system executes the hook in the hooking app's context; specifically, on the thread that called SetWindowsHookEx. This means that the hooking application must continue to pump messages or it might block the normal functioning of the 64-bit processes.

When I install the hook, I must pass a pointer to the hook callback function. However, that's a pointer that's only valid inside the process space of the application installing the hook. How does it use that pointer to call the correct code inside the address space of the application that is a target of the hook? Confused | :confused:

The difficult we do right away...
...the impossible takes slightly longer.

Richard MacCutchan15-Apr-20 4:57

15-Apr-20 4:57

Richard Andrew x64 wrote:
a pointer to the hook callback function.

The system keeps that address (which is the target of the hook) and uses it to call back into your application at the appropriate time (i.e when the relevant hook event triggers). But if you close your application, its address space is destroyed and the hook is no longer valid, so the system will no longer call it.

Richard Andrew x6415-Apr-20 5:49

15-Apr-20 5:49

Thank you for your response.

OK, so if the system calls back into my application at the appropriate time, why must the system load the DLL containing the filter function into each process that is hooked?

IOW, if the hook function is run inside the installing application, why must the hook function DLL be injected into every targeted application?

The difficult we do right away...
...the impossible takes slightly longer.

Richard MacCutchan15-Apr-20 6:05

15-Apr-20 6:05

Sorry I don't know the answer to that one. There is an implication that injecting the hook into another process can be done of the call-back function is in a dll. If that is the case then the dll must be associated withe the address space of that process. I must admit it is a long time since I used this feature so my recollection of it is not 100%.

Richard Andrew x6415-Apr-20 8:01

15-Apr-20 8:01

OK Thank you for your contributions thus far.

The difficult we do right away...
...the impossible takes slightly longer.

leon de boer16-Apr-20 0:21

16-Apr-20 0:21

You need an instance handle to load the DLL ... guess what happens to the instance handle when the application terminates Smile | :)

In vino veritas

Richard Andrew x6416-Apr-20 2:53

16-Apr-20 2:53

Yes, thank you. I progressed to the point where I'm creating the hook and processing it successfully.

But now the problem is that when the hook installer application terminates, it crashes all of the hooked applications *even though* I call UnhookWindowsHookEx() to remove the hook before terminating.

Would you have any hints what I can do about that?

The difficult we do right away...
...the impossible takes slightly longer.

leon de boer16-Apr-20 4:02

16-Apr-20 4:02

The unhook is usually just done in WM_DESTROY of the main application.
From memory it must be before you post WM_QUIT which will kill the instance handle.

In vino veritas

Richard Andrew x6416-Apr-20 6:12

16-Apr-20 6:12

Do you mean that the system waits until the window receives the WM_DESTROY message before it actually unhooks the hook?

Or do you mean that I must call UnhookWindowsHookEx BEFORE the WM_QUIT message is posted?

The difficult we do right away...
...the impossible takes slightly longer.

leon de boer16-Apr-20 6:25

16-Apr-20 6:25

Unhook it before you post the WM_QUIT message

In vino veritas

Accessing HDD drive

_Flaviu14-Apr-20 9:32

14-Apr-20 9:32

How is the way to open a HDD drive with _open function in such a way to read even the boot section of this drive ? Here is the code:

int hd_h = _open(device, O_BINARY | O_RDWR | O_EXCL);

device is provided with

"\\\\?\\E:"

This is the code from ntfs library GitHub - vitalif/ntfs-3g: Fork of git://ntfs-3g.git.sourceforge.net/gitroot/ntfs-3g/ntfs-3g with FIEMAP support patch[^]

Why I am asking that ? Even if _open return 3, further more, the reading of boot section has failed.

Function

ntfs_boot_sector_is_ntfs

say that my boot device is not NTFS:

if (! ntfs_boot_sector_is_ntfs(bs))
{
    errno = EINVAL;
    goto error_exit;
}

BOOL ntfs_boot_sector_is_ntfs(NTFS_BOOT_SECTOR* b)
{
	u32 i;
	BOOL ret = FALSE;
	ntfs_log_debug("Beginning bootsector check.\n");

	ntfs_log_debug("Checking OEMid, NTFS signature.\n");
	if (b->oem_id != const_cpu_to_le64(0x202020205346544eULL))	// "NTFS    "
	{
		ntfs_log_error("NTFS signature is missing.\n");  // <--- my code run by here
		goto not_ntfs;
	}
....

Of course, this debugging session ran as admin mode.

Re: Accessing HDD drive

Richard MacCutchan14-Apr-20 21:14