自己写一个简单的操作系统

1.参考文档

https://github.com/littleosbook/

2.宿主机环境

:~/lab/myOS# cat /etc/issue
Ubuntu 14.10 l

3.编译&链接OS内核

apt-get install build-essential nasm genisoimage bochs bochs-sdl(下载工具)

nasm -f elf32 loader.s(编译loader.s生成loader.o)

global loader ; the entry symbol for ELF

MAGIC_NUMBER equ 0x1BADB002 ; define the magic number constant
FLAGS equ 0x0 ; multiboot flags
CHECKSUM equ -MAGIC_NUMBER ; calculate the checksum
; (magic number + checksum + flags should equal 0)

section .text: ; start of the text (code) section
align 4 ; the code must be 4 byte aligned
    dd MAGIC_NUMBER ; write the magic number to the machine code,
    dd FLAGS ; the flags,
    dd CHECKSUM ; and the checksum

loader: ; the loader label (defined as entry point in linker script)
    mov eax, 0xCAFEBABE ; place the number 0xCAFEBABE in the register eax
.loop:
    jmp .loop ; loop forever

ld -T link.ld -melf_i386 loader.o -o kernel.elf(链接OS生成内核二进制文件)

ENTRY(loader) /* the name of the entry label */

SECTIONS {
    . = 0x00100000; /* the code should be loaded at 1 MB */
    .text ALIGN (0x1000) : /* align at 4 KB */
    {
        *(.text) /* all text sections from all files */
    }
    .rodata ALIGN (0x1000) : /* align at 4 KB */
    {
        *(.rodata*) /* all read-only data sections from all files */
    }
    .data ALIGN (0x1000) : /* align at 4 KB */
    {
        *(.data) /* all data sections from all files */
    }
    .bss ALIGN (0x1000) : /* align at 4 KB */
    {
        *(COMMON) /* all COMMON sections from all files */
        *(.bss) /* all bss sections from all files */
    }
}

wget http://littleosbook.github.com/files/stage2_eltorito(下载适合于ubuntu的grub)

4.打包OS内核生成iso镜像

#!/bin/bash
mkdir -p iso/boot/grub # create the folder structure
cp stage2_eltorito iso/boot/grub/ # copy the bootloader
cp kernel.elf iso/boot/ # copy the kernel
cp menu.lst iso/boot/grub/

genisoimage -R 
        -b boot/grub/stage2_eltorito 
        -no-emul-boot 
        -boot-load-size 4 
        -A os 
        -input-charset utf8 
        -quiet 
        -boot-info-table 
        -o os.iso 
        iso

其中menu.lst文件

default=0
timeout=0

title os
kernel /boot/kernel.elf

5.运行OS

bochs -f bochsrc.txt -q(注意远程终端运行会报错，提示sdl库不支持videomode，使用宿主机可以正常运行)

bothsrc.txt

megs: 32
display_library: sdl
romimage: file=/usr/share/bochs/BIOS-bochs-latest
vgaromimage: file=/usr/share/bochs/VGABIOS-lgpl-latest
ata0-master: type=cdrom, path=os.iso, status=inserted
boot: cdrom
log: bochslog.txt
clock: sync=realtime, time0=local
cpu: count=1, ips=1000000

6.验证OS正常运行

点击弹出的窗口右上角的power关机，可以看到bochslog.txt中显示

02604562000i[CPU0 ] | RAX=00000000cafebabe  RBX=000000000002cd80