Writing OS in 1000 lines

This is a very small toy OS written in about 1000 lines following the below guide.

https://operating-system-in-1000-lines.vercel.app/ja/welcome

$ tokei *.c *.h *.ld
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
 Language            Files        Lines         Code     Comments       Blanks
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
 C                       6         1112          861          114          137
 C Header                3           98           75            8           15
 LD Script               2           78           48           15           15
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
 Total                  11         1288          984          137          167
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Files

• common.c, common.h : Common libraries shared by both kernel and user (e.g. printf, memset)
• Kernel land
  • kernel.h : Constants and declarations shared within kernel
  • kernel.c : Entry point, allocation, paging, system calls, exception handler
  • fs.c : Device (virtio-blk) driver and filesystem
  • proc.c : Multiple processes management with context switch
  • kernel.ld : Linker script for memory layout of kernel land
• User land
  • stdlib.c, stdlib.h : Standard library
  • shell.c : Command line shell (user program)
  • user.ld : Linker script for memory layout of user land
• disk/*.txt : Filesystem content
• Makefile : Build script
• run.bash : Script to run kernel with QEMU
• env.sh : Script to prepare development environment (for macOS)

How to build

source env.sh  # For macOS
make

How to run QEMU

./run.bash

References

• RISC-V specification: https://github.com/riscv/riscv-isa-manual/releases/download/Priv-v1.12/riscv-privileged-20211203.pdf
• QEMU virt machine: https://www.qemu.org/docs/master/system/riscv/virt.html
• Open SBI specification releases: https://github.com/riscv-non-isa/riscv-sbi-doc/releases
• VIRTIO specification: https://docs.oasis-open.org/virtio/virtio/v1.1/csprd01/virtio-v1.1-csprd01.html