Linux Subsystem for Windows 9x

WSL9x is an experimental project that cooperatively runs a modern Linux 6.19 kernel inside the Windows 9x kernel.

Since it does not use hardware virtualization, it can run even on a 486, and its goal is to run Windows 9x and Linux applications together without rebooting.

The architecture is divided into three parts.

• Patched Linux kernel: based on the win9x-um-6.19 branch
• VxD driver: handles initialization, memory mapping, page faults, and syscall dispatch
• wsl.com client: a 16-bit DOS program that acts as a TTY

System calls are handled via a GPF handler instead of int 0x80. Due to constraints in Windows 9x's interrupt descriptor table, exceptions are intercepted and forwarded to Linux system calls.

On the Linux side, a User-Mode Linux base has been modified to call Windows 9x kernel APIs, and it runs in ring 0. Console output makes use of the DOS window, delivering characters and control sequences to the screen via int 0x29 and an ANSI driver.

Building requires the i386-linux-musl cross toolchain, Open Watcom v2, the patched Linux kernel, and a disk image with Windows 9x installed. The project is released under GPL-3.