A Microsoft unrelated enthusiast has developed the WSL9x (Windows 9x Subsystem for Linux) toolkit, allowing modern Linux kernels to run within the Windows 95/98/ME kernel. The project enables running Linux and Windows 9x applications side by side in a single system, similar to how the WSL layer allows working with Linux applications in modern versions of Windows. Only console Linux programs are supported. The code for WSL9x components is written in C and assembly and is distributed under the GPLv3 license.
Unlike WSL2, WSL9x does not use virtualization, and the Linux kernel runs in zero-ring protection alongside the Windows kernel, allowing WSL9x to be used on systems without hardware virtualization support, even with an i486 CPU. The system uses a modified Linux kernel 6.19, compiled to operate in User-mode Linux (UML), designed to run the kernel as a user process. Calls to the POSIX API in the UML layer are replaced with calls to the Windows 9x kernel API.
A VxD driver prepared by the project is loaded into Windows, responsible for initializing the WSL9x subsystem, loading and placing the Linux kernel in memory, interrupt dispatching, cyclic control transfer to the Linux kernel in cooperative multitasking mode, and handling Linux-kernel-addressed events from user space, such as executing system calls and accessing unallocated memory pages (page faults). Since the Windows 9x kernel does not support the interrupt descriptor table (IDT), which does not allow setting a custom interrupt handler for 0x80, the GPF (General Protection Fault) handler is used for system calls, intercepting exceptions that occur during the execution of the SYSCALL instruction.
A utility called wsl.com is offered to users, designed as a 16-bit DOS application that allows the use of the MS-DOS command line to run Linux programs. This utility provides input event transmission and simulates console functionality to display output with ANSI escape code support.
Forrás: opennet.ru
