mos

mOS

mOS is the UNIX-like operating system developed from scratch and aims to be POSIX compliant.

Work-in-process features

• Filesystem
• Program loading
• UI (X11)
• Log
• Networking
• Signal
• Terminal
• mOS toolchain
• Port figlet
• Libc
• Port GNU Bash, Coreutils
• Unit testing
• Dynamic linker
• Port GCC (the GNU Compiler Collection)
• Browser
• Sound
• Symmetric multiprocessing

? Optional features

• Setup 2-level paging in boot.asm

Get started

MacOS

• install packages

  $ brew install qemu nasm gdb i386-elf-gcc i386-elf-grub bochs e2fsprogs xorriso
  

• open your bash config and add lines below. Depending on your bash config, the file might be different. I use ohmyzsh, so it is .zshrc

  # .zshrc
  alias grub-file=i386-elf-grub-file
  alias grub-mkrescue=i386-elf-grub-mkrescue
  

• run emulator

  $ cd src && mkdir logs
  $ ./create_image.sh && ./build.sh qemu iso
  

• open another terminal

  $ cd src
  $ gdb isodir/boot/mos.bin
  # in gdb
  (gdb) target remote localhost:1234
  (gdb) c
  

✍? If you get this error hdiutil: attach failed - no mountable file systems, installing extFS for MAC might help

Ubuntu

• Install packakges

  $ sudo apt install build-essential autopoint bison gperf texi2html texinfo qemu automake-1.15 nasm xorriso qemu-system-i386

• Install gcc cross compilier via https://wiki.osdev.org/GCC_Cross-Compiler#The_Build

• Install GCC (Version 9.1.0) & Binutils (Version 2.32).

• Open src/toolchain/build.sh and modify SYSROOT and PREFIX variables to fit in your case

  PREFIX="$HOME/opt/cross"
  TARGET=i386-pc-mos
  # SYSROOT cannot locate inside PREFIX
  SYSROOT="$HOME/Projects/mos/src/toolchain/sysroot"
  JOBCOUNT=$(nproc)
  

• Install mos toolchain

  $ cd src/toolchain
  $ ./build.sh
  

• Run Emulator

  $ cd src && mkdir logs
  $ ./create_image.sh
  $ cd ports/figlet && ./package.sh && cd ../..
  $ cd ports/bash && ./package.sh make && cd ../..
  $ cd ports/coreutils && ./package.sh make && cd ../..
  $ ./build.sh qemu iso
  

• Open another terminal

  $ cd src
  $ gdb isodir/boot/mos.bin
  # in gdb
  (gdb) target remote localhost:1234
  (gdb) c
  

✍️ To get userspace address for debugging

$ i386-mos-readelf -e program
# find the line below and copy Addr
# [Nr] Name              Type            Addr     Off    Size   ES Flg Lk Inf Al
# [ x] .text             PROGBITS        xxx      xxx    xxx    00 AX   0   0  4

Unit Test

$ cd test && git clone https://github.com/ThrowTheSwitch/Unity.git unity
$ make clean && make

Debugging

in build.sh, adding -s -S right after qemu to switch to debug mode. Currently, I use vscode + native debug -> click Run -> choose "Attach to QEMU"

Monitoring

by default, mOS logs output to terminal. If you want to monitor via file, doing following steps

# src/build.sh#L71
-serial stdio
↓
-serial file:logs/uart1.log

$ tail -f serial.log | while read line ; do echo $line ; done

✍? Using tail in pipe way to color the output (like above) causes a delay -> have to manually save in the IDE to get latest changes

References

Tutorials

• http://www.brokenthorn.com/Resources
• http://www.jamesmolloy.co.uk/tutorial_html/
• https://wiki.osdev.org

Ebooks

• Understanding the Linux Kernel, 3rd Edition by Daniel P. Bovet; Marco Cesati