teapot9 / cos

Hobby operating system

• Mainly developped in C.
• Boots with UEFI.
• Does not do anything meaningful.

This repository

Source code structure

• arch/*: architecture-specific code
  • boot: early boot (after firmware, before kernel_main)
  • *: same as non-arch
• dev: device drivers
• include
• kernel: core kernel components (task management, core functions)
• lib: hardware independant code (ELF, string manipulation, generic structures)
• mm: memory management

Other directories

• build: directory generated by ./boot script for QEMU
• scripts: helper scripts
• third_party: external libraries dependencies

Utilities

• ./boot: script to boot the kernel
  • ./boot efi ARGS: starts kernel with QEMU (ARGS are passed to QEMU)
  • ./boot egdb ARGS: starts GDB and use the uefi.py lib to debug kernel
• uefi.py: GDB library to load kernel symbols during boot
  • GDB command efi: automatically called by ./boot egdb:
    • load kernel symbols to 2 positions:
      • the address where EFI has loaded the kernel
      • the address where the kernel relocates
    • read the auto.gdb file
  • GDB command qq: kill kernel and quit
  • GDB command rbreakif: like rbreak but supports a condition
• auto.gdb: commands to run automatically by uefi.py
  • lines starting with # are ignored
  • lines starting with @ don't produce output to GDB console
  • lines starting with * are executed on when breakpoint is reached (last created breakpoint)
  • other lines are executed normally

Build

Dependencies

• Linux kernel Kconfig: conf and mconf executables must be in PATH

Compilation

• Configure with make menuconfig
• Build with make

Run

Boot with GDB in a single terminal:

Run the following boot shell function:

boot() { ./boot efi ${QEMU_ARGS} & ./boot egdb "$@" ; kill -0 $! 1>/dev/null 2>&1 && kill $! ; killall qemu-system-x86_64; }

Extra args are passed to GDB. QEMU_ARGS environment variable is passed to QEMU as extra args.

Boot with GDB in 2 terminal (for GDB and QEMU console):

• Terminal 1: ./boot efi -monitor stdio -display none
• Terminal 2: ./boot egdb

Build system

Each directory has:

• A Kconfig file
• A Makefile which lists needed object files:
  • all files in the obj-y variable will be built in the final kernel
  • all files in the bootloader-y variable will be built in the bootloader (stage 1 kernel)
  • Makefile structure (in order):
    • include Makefile.flags
    • define variables (obj-y, ...)
    • include Makefile.rules
    • define build rules specific to this directory

Compilation generates in each directory:

• *.o files for the final kernel
• *.bootloader.o for the bootloader
• modules.o: all *.o files merged
• bootloader.o: all *.bootloader.o files merged
• *.d files corresponding to their *.o counterpart