A Unix-like kernel for RISC-V

Written from scratch in C and RV64 assembly — page tables, preemptive scheduling, a custom filesystem, and VirtIO drivers. Below it is booting under QEMU and running real games in user mode.

rv64 Sv39 paging preemptive multitasking KTFS VirtIO ELF loader fork / exec / wait 

        

    

    


    

        
What you're looking at

        

            These are real recordings of the kernel running, not mockups. Each one boots
            from nothing, brings up the subsystems, mounts a filesystem off an emulated
            disk, loads an ELF binary into a fresh address space, and drops into user mode.
            The games are unmodified 1970s–80s BSD and Infocom programs compiled for
            RISC-V; the kernel underneath them is the project.
        

    


    

        
Subsystems

        

            

                Memory
                Sv39 three-level page tables, per-process address spaces, kernel/user separation
            

            

                Scheduling
                Preemptive multitasking with timer-driven context switching
            

            

                Traps
                Exception and interrupt handling, PLIC-backed external interrupts
            

            

                Filesystem
                KTFS, a custom on-disk filesystem, with a write-back block cache
            

            

                Syscalls
                fork, exec, wait, and I/O across the user/kernel boundary
            

            

                Devices
                VirtIO block and RNG, 16550 UART, RTC, ramdisk, behind a common device abstraction
            

            

                Loader
                ELF loader that maps user binaries into fresh address spaces
            

        

    


    

        
Run it yourself

        

            Everything above reproduces on any machine with Docker — no RISC-V
            toolchain needed:
        

        

            

                 
                git clone https://github.com/jkcol/operating-systems-kernel

                    cd operating-systems-kernel && ./demo/demo.sh		
            

        

        

            The demo build targets a stock qemu-system-riscv64, which provides a
            single UART. The kernel was written against a course-patched QEMU that had
            several, so the demo entry point shares one UART between the kernel console and
            the user program. Everything else is the unmodified kernel.