ID Number: Q74810
3.00 3.10
WINDOWS
Summary:
Some device drivers need to call functions provided by the user
dynamic-link library (DLL) of Microsoft Windows. The MessageBox
function is an example of one of these functions. However, a driver
cannot implicitly link to the user DLL. If a driver attempts to
implicitly link to user, it will fail to load and Windows will not
run. The load fails because the drivers are loaded before user (user
requires the drivers). An implicit link to user forces the kernel to
load the user module when the driver is loaded; which Windows cannot
do. Therefore, the driver must establish the link at a later time.
This article explains how this is accomplished.
More Information:
An example of a driver calling a function in user is the
communications driver (COMM.DRV) which displays a message box to
resolve contention on the serial and parallel ports.
The source code for COMM.DRV is included in the Windows Device
Development Kit (DDK). The driver's Contention_Dlg function displays
dynamically links to user and displays the message box. For Windows
3.1, the Contention_Dlg function is in the IBMSETUP.ASM file; for
Windows 3.0 this function is in the IBMCOM.ASM file.
There are two steps required:
1. Use GetModuleHandle("user") to retrieve the module handle to user.
2. Call GetProcAddress(hUserModule, "MESSAGEBOX") to retrieve the FAR
procedure address of the MessageBox function.
Use this procedure address to call the function from the driver.
Additional reference words: 3.00 3.10 DDKMISC