Re: Access violation when hook is installed; after WM_NCDESTROY of SysShadow window

"Bob S" <>
Thu, 26 Jul 2007 13:33:31 +0530
Its amazing how much the process of writing down ones thoughts can help!
Just as I wrote "I suspect a stack corruption" and sent the message, it
struck me that the problem might be with the calling convention. Sure enough
my HookProc did not specify 'CALLBACK' (__stdcall) and that was causing the
stack corruption.

Thanks for your help


"Joseph M. Newcomer" <> wrote in message

See below...
On Wed, 25 Jul 2007 17:21:10 +0530, "Bob S" <> wrote:

Here is the code I use :

m_hhook = SetWindowsHookEx(WH_CALLWNDPROC, (HOOKPROC)HookProc, NULL,

Did you check to see that this is a non-NULL return value?

LRESULT HookProc(int nCode, WPARAM wParam, LPARAM lParam)
return CallNextHookEx(viewData->m_hhook, nCode, wParam, lParam);
HookProc is a global function.
viewData is a global variable whose m_hhook member stores the HHOOK.

So you are only hooking the current process, and in particular, the
current thread. This
was not previously stated.

Am I doing anything wrong?

Except that you have not demonstrated that you have checked for a
successful return, and
therefore have no idea if the m_hhook value is actually valid, I don't see
anything wrong
here. Also, even if the value is correctly saved when you
CallWindowsHookEx, are you sure
that value is still the same at the point where you CallNextHookEx? I
would suggest
adding the following two lines:

at the SetWindowsHookEx site
TRACE(_T("Hook set, HHOOK = %p\n"), viewData->m_hhook);

at the CallNextHookEx site:
TRACE(_T("CallNextHookEx(%p,...)\n"), viewData->m_hhook);

to make sure something hasn't clobbered the values somehow in between
times. You might be
the victim of a drive-by memory clobber.


"Joseph M. Newcomer" <> wrote in message

Show the empty example that crashes. Full code of the DLL, just setting
the hook and
handling it. Make sure your HHOOK is in the shared data segment.

On Tue, 24 Jul 2007 19:28:59 +0530, "Bob S" <>

The violation occurs even if I have an empty hook proc with just a call

I have also confirmed that the violation does not occur if I disable the
"Show shadows under menus" option in Desktop Appreances page.

The call stack and assembly code at violation point is copied below.
Stranegly, my code is not even in the
picture in the call stack, but nonethless the error occurs if

-the hook is installed
-the "Show shadows under menus" option in Desktop Appreances page is
-When a visible tooltip gets destroyed sometime after the WM_NCDESTROY
message of the 'SysShadow' window associated with a tooltip

call stack

Code at 77D4E63B

77D4E63B mov eax,dword ptr [esi]
77D4E63D mov eax,dword ptr [eax+9Ch]
77D4E643 test eax,eax
77D4E645 jne 77D50151
77D4E64B push 0
77D4E64D push 0Ch
77D4E64F pop edx
77D4E650 lea ecx,[ebp-0Ch]
77D4E653 mov dword ptr [ebp-0Ch],edi
77D4E656 call 77D494C9
77D4E65B pop edi
77D4E65C pop esi
77D4E65D leave
77D4E65E ret 4
77D4E661 nop
77D4E662 nop
77D4E663 nop
77D4E664 nop
77D4E665 nop
77D4E666 mov eax,1163h
77D4E66B mov edx,7FFE0300h
77D4E670 call dword ptr [edx]
77D4E672 ret 4
77D4E675 nop
77D4E676 nop
77D4E677 nop
77D4E678 nop
77D4E679 nop
77D4E67A mov edi,edi
77D4E67C push ebp
77D4E67D mov ebp,esp
77D4E67F sub esp,10h
77D4E682 push esi
77D4E683 mov esi,dword ptr [ebp+0Ch]
77D4E686 test esi,0FFFE0000h
77D4E68C jne 77D76FB1
77D4E692 mov eax,dword ptr [ebp+18h]
77D4E695 test eax,0FFFFFFF0h
77D4E69A jne 77D76FB1
77D4E6A0 push edi
77D4E6A1 mov edi,dword ptr [ebp+20h]
77D4E6A4 test edi,edi
77D4E6A6 je 77D4E6AB
77D4E6A8 and dword ptr [edi],0
77D4E6AB and dword ptr [ebp-8],0
77D4E6AF and dword ptr [ebp-4],0
77D4E6B3 mov dword ptr [ebp-10h],eax
77D4E6B6 mov eax,dword ptr [ebp+1Ch]
77D4E6B9 mov dword ptr [ebp-0Ch],eax
77D4E6BC mov eax,dword ptr [ebp+8]
77D4E6BF cmp eax,0FFFFFFFFh


"Joseph M. Newcomer" <> wrote in message

See below...
On Tue, 24 Jul 2007 16:42:59 +0530, "Bob S" <>

I am setting a WH_CALLWNDPROC hook for the current thread using
When interacting with the file open/save dialogs of applications, I
'access violation' whenever a tooltip is about to be destroyed. The
is associate with a shadow window having class name 'SysShadow' ; this
window receives the WM_NCDESTROY message. My hook receives all
this point. However, the crash occurs next ......

Show your hook code. It would also be useful if we knew what function
lurking at
77D4e63b. But the detail level here doesn't help if we don't know
the actual code is
trying to do.

First-chance exception at 0x77d4e63b in notepad.exe: 0xC0000005:
violation reading location 0x00000000.
Unhandled exception at 0x77d4e63b in notepad.exe: 0xC0000005: Access
violation reading location 0x00000000.

Contents of 77D4E63B are as follows :

77D4E63B mov eax,dword ptr [esi] // esi is 0 here
77D4E63D mov eax,dword ptr [eax+9Ch]
77D4E643 test eax,eax
77D4E645 jne 77D50151
77D4E64B push 0
77D4E64D push 0Ch

I appreciate any help!


Joseph M. Newcomer [MVP]
MVP Tips:

Joseph M. Newcomer [MVP]
MVP Tips:

Joseph M. Newcomer [MVP]
MVP Tips:

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