91 lines
4.3 KiB
Plaintext
91 lines
4.3 KiB
Plaintext
|
|
||
|
|
SOS: A Simple Operating System
|
||
|
|
|
||
|
|
|
||
|
|
This is SOS, a Simple Operating System for i386-family
|
||
|
|
processors. This is as simple as possible to show a way to program a
|
||
|
|
basic Operating System on real common hardware (PC). The code should
|
||
|
|
be easily readable and understandable thanks to frequent comments, and
|
||
|
|
references to external documentation. We chose to implement the basic
|
||
|
|
features of an OS, thus making design decisions targetting towards
|
||
|
|
simplicity of understanding, covering most of the OS classical
|
||
|
|
concepts, but not aiming at proposing yet another full-fledged
|
||
|
|
competitive OS (Linux is quite good at it). However, for those who
|
||
|
|
would like to propose some enhancements, we are open to any code
|
||
|
|
suggestions (patches only, please). And yes, there might be bugs in
|
||
|
|
the code, so please send us any bug report, and/or patches !
|
||
|
|
|
||
|
|
The OS comes as a set of articles (in french) to be published in the
|
||
|
|
journal "Linux Magazine France". Each month, the part of the code
|
||
|
|
related to the current article's theme is released (see VERSION file),
|
||
|
|
and the resulting OS can be successfully compiled and run, by booting
|
||
|
|
it from a floppy on a real machine (tested AMD k7, Cyrix and Intel P4
|
||
|
|
pentiums), or through an x86 emulator (bochs or qemu). The resulting
|
||
|
|
OS is available as a multiboot compliant ELF kernel (sos.elf) and as a
|
||
|
|
floppy image (fd.img). It provides a very very very basic demo whose
|
||
|
|
aim is to understand how everything works, not to animate sprites on
|
||
|
|
the screen with 5:1 dolby sound.
|
||
|
|
|
||
|
|
The initial technical features and lack-of-features of the OS are:
|
||
|
|
- monolithic kernel, fully interruptible, non-preemptible (big kernel
|
||
|
|
lock), target machines = i386 PC or better
|
||
|
|
- compiles on any host where the gcc/binutils toolchain (target
|
||
|
|
i586-gnu) is available. Can be tested on real i486/pentium
|
||
|
|
hardware, or on any host that can run an i486/pentium PC emulator
|
||
|
|
(bochs or qemu)
|
||
|
|
- kernel loaded by grub, or by a sample bootsector (up to article 2
|
||
|
|
ONLY)
|
||
|
|
- clear separation of physical memory and virtual memory concepts,
|
||
|
|
even inside the kernel: no identity-mapping of the physical memory
|
||
|
|
inside the kernel (allows to move virtual mappings of kernel pages
|
||
|
|
at run-time, eg to free ISA DMA pages, and to avercome the 4G RAM
|
||
|
|
barrier)
|
||
|
|
- slab-type kernel memory allocation
|
||
|
|
- no swap, no reverse mapping
|
||
|
|
- VERY simple drivers: keyboard, x86 video memory, IDE disks
|
||
|
|
- logical devices: partitions, FAT filesystem, "hard-coded"
|
||
|
|
mountpoints only (~ MSDOS)
|
||
|
|
- no network stack
|
||
|
|
- user-level features: ELF loader (no shared libraries), processes,
|
||
|
|
user threads (kernel-level scheduling only), mmap API, basic VFS
|
||
|
|
|
||
|
|
To understand where to look at for what, here is a brief description:
|
||
|
|
- Makefile: the (ONLY) makefile of the OS. Targets are basically
|
||
|
|
'all' and 'clean'
|
||
|
|
- bootstrap/ directory: code to load the kernel. Both the stuff
|
||
|
|
needed for a multiboot-compliant loader (eg grub) AND a bootsector
|
||
|
|
are provided. The bootsector may only be used up to article 2.
|
||
|
|
- sos/ directory: the entry routine for the kernel (main.c), various
|
||
|
|
systemwide header files, a set of common useful C routines
|
||
|
|
("nano-klibc"), and kernel subsystems (kernel memory management,
|
||
|
|
etc...)
|
||
|
|
- hwcore/ directory: Low-level CPU- and kernel-related routines
|
||
|
|
(interrupt/exception management, translation tables and segment
|
||
|
|
registers, ...)
|
||
|
|
- drivers/ directory: basic kernel drivers for various (non CPU)
|
||
|
|
devices (keyboard, x86 video memory, bochs 0xe9 port, ...). Used
|
||
|
|
mainly for debugging
|
||
|
|
- support/ directory: scripts and configuration files to build the
|
||
|
|
floppy images
|
||
|
|
- extra/ directory: a set of configuration files to be customized for
|
||
|
|
non-x86 host installations (yes, we primarily develop SOS on a ppc, for
|
||
|
|
the x86 target of course), or for grub-less installations. See
|
||
|
|
README file in this directory.
|
||
|
|
|
||
|
|
The code is licensed under the terms of the GNU GPL version 2 (see
|
||
|
|
LICENSE file).
|
||
|
|
|
||
|
|
Enjoy !
|
||
|
|
|
||
|
|
David Decotigny, Thomas Petazzoni, the Kos team
|
||
|
|
http://sos.enix.org/
|
||
|
|
http://david.decotigny.free.fr/
|
||
|
|
http://kos.enix.org/~thomas/
|
||
|
|
http://kos.enix.org/
|
||
|
|
|
||
|
|
|
||
|
|
--
|
||
|
|
David Decotigny
|
||
|
|
|
||
|
|
PS: Made with a Mac.
|