For Reasons™, I needed to be able to compile and debug drivers for Windows 98. This meant setting up the DDK (Driver Development Kit) and Visual C++. So that this knowledge isn't lost, here's a quick guide.¹

• Prerequisites
• Installation
• Building drivers
• Screenshots
  • Final config.sys
  • Debugger break-in
  • Boot with debugger
  • Driver output

Prerequisites

1. A Windows 98 ISO.
   • For instance, from WinWorld. Be sure to get "OEM Full" version.
2. The DDK.
   • For instance, this page has a bunch of useful downloads.
   • Specifically, get the complete DDK with patches (that's what worked for me): https://www.mdgx.com/spx/98DDK.RAR.
3. Visual C++ 5.0.
   • Again, WinWorld to the rescue.

Installation

1. Install Windows on a VM.
   • WinWorld says that Windows 98 might have trouble running on a VM, so you may want to consider 86Box or PCem instead.
   • In any case, make sure the VM has a serial port exposed to the host (through a pipe or some such).
2. Install Visual C++.
   • To be on the safe side, install everything.
3. Install the DDK.
   • Again, install everything.
   • Important: increase the environment space by adding the following line to config.sys: shell=c:\command.com /p /e:4096
4. Check the installation by building the samples.
   • Open a "Checked Build Environment" command prompt from the start menu, go to C:\98DDK\src, and run build -cZ
   • There will be a few errors, but most of the samples will compile. The binaries will be at C:\98DDK\lib\i386\checked.
5. Check that debugging works.
   1. Reboot into DOS mode and run \98ddk\bin\wdeb386 /c:1 /r:19200 \windows\win.com
      • This starts the debugger on COM port 1 (on the guest), with a baud rate of 19200, and instructs it to run the kernel at \windows\win.com.
   2. On the host, connect to the VM's serial port with the correct baud rate and press Ctrl-C.
      • The debugger should break in (see screenshot below).
   3. Enter g to resume execution.
6. Make sure the debugger starts on boot.
   1. Add the following line to config.sys: DEVICE=C:\98ddk\bin\wdeb386.exe /c:1 /r:19200
      • Note: I'm not sure about the importance of the line order in this file. In my setup this line comes before the one that increases environment space (see screenshot below).
   2. Reboot and check that this works. On boot, the debugger should print a version string (see screenshot below).

Note: the debugger we're using here is WDEB386. There's a better debugger installed with the DDK — WDEB98 — but it requires the use of a special client — RTerm98 — which complicates matters. So that we can use PuTTY, we're sticking with the old debugger.

Building drivers

Now that the environment is all set up, you may want to actually write your own driver in it. Here's a gist of a minimal WDM driver project. To build it:

1. Put all files in the same directory.
2. Inside said directory, create the path bin\i386\checked
3. Open a "Checked Build Environment" command prompt.
4. From within the directory, run build -cZ

To make the driver load on boot, place the binary in C:\WINDOWS\SYSTEM32\DRIVERS and run the supplied .reg file.

Fun fact: the built binary also runs on Windows 10 😎.

Screenshots

Final config.sys

Debugger break-in

Boot with debugger

Driver output