Article: Q110661
Product(s): Microsoft Windows Software Development Kit
Version(s): WINDOWS:3.1
Operating System(s):
Keyword(s): kb16bitonly kbHook kbSDKPlatform
Last Modified: 09-JUN-1999
3.10
WINDOWS
kbprg kbprb
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The information in this article applies to:
- Microsoft Windows Software Development Kit (SDK) 3.1
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SYMPTOMS
========
An application that installs a WH_CBT hook function that is run along with the
HOOKS sample application will cause a General Protection Fault (GPF) in the
system if the computer-based training (CBT) hook is enabled and the hook
procedure receives a CBT notification.
CAUSE
=====
In the HOOKS sample, CBTFunc() is incorrectly casting lParam (a DWORD value) to
a WORD when it calls CallNextHookEx() to pass the info on to the next hook in
the hook chain. This causes the receiving hook function to receive the CBT
notification with a modified lParam (the HIWORD stripped off), thus translating
to an invalid pointer and eventually causing a GPF.
A GPF occurs similarly when an application that installs a WH_CALLWNDPROC hook is
run along with the HOOKS sample and the CallWndProc hook menu-item is selected.
In the same manner, the HOOKS sample function CallWndProcFunc() incorrectly
casts its lParam (a DWORD value) to a WORD on its call to CallNextHookEx().
In addition, the HOOKs sample will GPF when the WH_JOURNALRECORD hook is
installed and some other application calls SetSysModalWindow(). As mentioned in
the Windows 3.1 SDK help,
If a WH_JOURNALRECORD hook is in place when SetSysModalWindow is called,
the hook is called with a hook code of <B>HC_SYSMODALON</B> (for turning on the system-modal window) or <B>HC_SYSMODALOFF</B> (for turning off the system-modal window).
RESOLUTION
==========
Modify both the CBTFunc() and CallWndProcFunc() calls to CallNextHookEx() to
correctly cast lParam to a DWORD.
In the case of the journal record hook, make the following change to the function
JournalRecordFunc in hooksdll.c:
if( nCode >= 0) {
// do not record if SysModalOn or SysModalOff and let other filter know
// about it.
if(nCode == HC_SYSMODALON || nCode == HC_SYSMODALOFF)
{
// let other hook filters know about this
CallNextHookEx(hhookHooks[JOURNALRECORDINDEX], nCode, wParam,
lParam);
return;
}
STATUS
======
This behavior is by design.
Additional query words: 3.10 gpf gp-fault
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Keywords : kb16bitonly kbHook kbSDKPlatform
Technology : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK310
Version : WINDOWS:3.1
Issue type : kbprb
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