90 lines
4.3 KiB
Plaintext
90 lines
4.3 KiB
Plaintext
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SOS: A Simple Operating System
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This is SOS, a Simple Operating System for i386-family
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processors. This is as simple as possible to show a way to program a
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basic Operating System on real common hardware (PC). The code should
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be easily readable and understandable thanks to frequent comments, and
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references to external documentation. We chose to implement the basic
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features of an OS, thus making design decisions targetting towards
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simplicity of understanding, covering most of the OS classical
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concepts, but not aiming at proposing yet another full-fledged
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competitive OS (Linux is quite good at it). However, for those who
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would like to propose some enhancements, we are open to any code
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suggestions (patches only, please). And yes, there might be bugs in
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the code, so please send us any bug report, and/or patches !
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The OS comes as a set of articles (in french) to be published in the
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journal "Linux Magazine France". Each month, the part of the code
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related to the current article's theme is released (see VERSION file),
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and the resulting OS can be successfully compiled and run, by booting
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it from a floppy on a real machine (tested AMD k7, Cyrix and Intel P4
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pentiums), or through an x86 emulator (bochs or qemu). The resulting
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OS is available as a multiboot compliant ELF kernel (sos.elf) and as a
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floppy image (fd.img). It provides a very very very basic demo whose
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aim is to understand how everything works, not to animate sprites on
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the screen with 5:1 dolby sound.
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The initial technical features and lack-of-features of the OS are:
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- monolithic kernel, fully interruptible, non-preemptible (big kernel
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lock), target machines = i386 PC or better
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- compiles on any host where the gcc/binutils toolchain (target
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i586-gnu) is available. Can be tested on real i486/pentium
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hardware, or on any host that can run an i486/pentium PC emulator
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(bochs or qemu)
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- kernel loaded by grub or by a sample bootsector
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- clear separation of physical memory and virtual memory concepts,
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even inside the kernel: no identity-mapping of the physical memory
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inside the kernel (allows to move virtual mappings of kernel pages
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at run-time, eg to free ISA DMA pages, and to avercome the 4G RAM
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barrier)
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- slab-type kernel memory allocation
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- no swap, no reverse mapping
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- VERY simple drivers: keyboard, x86 video memory, IDE disks
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- logical devices: partitions, FAT/ext2 filesystem, Unix-style
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mountpoints, hard/soft links
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- basic network stack (ARP/IP/UDP)
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- user-level features: ELF loader (no shared libraries), processes,
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user threads (kernel-level scheduling only), mmap API, basic VFS
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To understand where to look at for what, here is a brief description:
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- Makefile: the (ONLY) makefile of the OS. Targets are basically
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'all' and 'clean'
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- bootstrap/ directory: code to load the kernel. Both the stuff
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needed for a multiboot-compliant loader (eg grub) AND a bootsector
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are provided.
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- sos/ directory: the entry routine for the kernel (main.c), various
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systemwide header files, a set of common useful C routines
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("nano-klibc"), and kernel subsystems (kernel memory management,
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etc...)
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- hwcore/ directory: Low-level CPU- and kernel-related routines
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(interrupt/exception management, translation tables and segment
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registers, ...)
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- drivers/ directory: basic kernel drivers for various (non CPU)
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devices (keyboard, x86 video memory, bochs 0xe9 port, ...). Used
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mainly for debugging
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- support/ directory: scripts and configuration files to build the
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floppy images
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- extra/ directory: a set of configuration files to be customized for
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non-x86 host installations (yes, we primarily develop SOS on a ppc, for
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the x86 target of course), or for grub-less installations. See
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README file in this directory.
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The code is licensed under the terms of the GNU GPL version 2 (see
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LICENSE file).
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Enjoy !
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David Decotigny, Thomas Petazzoni, the Kos team
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http://sos.enix.org/
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http://david.decotigny.free.fr/
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http://kos.enix.org/~thomas/
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http://kos.enix.org/
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--
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David Decotigny
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PS: Made with a Mac.
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