操作系统之旅（003）—— 编译bootsect.s
下载linux0.11内核源代码(下载地址)
将下载好的源代码放到共享文件夹下，从Ubuntu中打开共享文件夹即能看到源代码，拷贝到Ubuntu下，不要再共享文件夹下操作源代码。
cd到linux-0.11.tar.gz所在目录，输入命令：tar zxvf linux-0.11.tar.gz
cd到linux-0.11目录下，输入命令：make all
安装完成后，执行命令：make all
as86汇编程序笔者找不到可以在Ubuntu上运行的，决定采用nasm重写bootsect.s和setup.s。
首先安装nasm，执行命令：sudo apt install nasm
安装完成后，执行命令：nasm boot/bootsect.s -o bootsect.bin
根据错误提示修改bootsect.s文件
【！】和【/**/】注释语句改为【；】开始的注释语句，多处修改
引用宏或立即数不需要前面的#，多处修改
.byte 和 .ascii 改为 db，多处修改
.word 改为 dw，多处修改
引用内存的地方需要加[]，如inc track改为inc word [track]
删除25-32行
.globl begtext, begdata, begbss, endtext, enddata, endbss
.text
begtext:
.data
begdata:
.bss
begbss:
.text删除45行
entry startrep
movw为
rep movsw修改56行
jmpi go,INITSEG为
jmp INITSEG:go修改77行
j load_setup为
jmp load_setup修改87行
seg cs
mov sectors,cx
为
mov [cs:sectors], cx修改237行
outb为
out dx, al修改249行
.orgtimes 508-($-$$) db 0.text
endtext:
.data
enddata:
.bss
endbss:执行命令：nasm boot/bootsect.s -o bootsect.bin
无错误提示，生成bootsect.bin。**************************************************************************************************************
bootsect.s修改后源代码：
;
; SYS_SIZE is the number of clicks (16 bytes) to be loaded.
; 0x3000 is 0x30000 bytes = 196kB, more than enough for current
; versions of linux
;
SYSSIZE equ 0x3000
;
; bootsect.s (C) 1991 Linus Torvalds
;
; bootsect.s is loaded at 0x7c00 by the bios-startup routines, and moves
; iself out of the way to address 0x90000, and jumps there.
;
; It then loads 'setup' directly after itself (0x90200), and the system
; at 0x10000, using BIOS interrupts.
;
; NOTE! currently system is at most 8*65536 bytes long. This should be no
; problem, even in the future. I want to keep it simple. This 512 kB
; kernel size should be enough, especially as this doesn't contain the
; buffer cache as in minix
;
; The loader has been made as simple as possible, and continuos
; read errors will result in a unbreakable loop. Reboot by hand. It
; loads pretty fast by getting whole sectors at a time whenever possible.
SETUPLEN equ 4 ; nr of setup-sectors
BOOTSEG equ 0x07c0 ; original address of boot-sector
INITSEG equ 0x9000 ; we move boot here - out of the way
SETUPSEG equ 0x9020 ; setup starts here
SYSSEG equ 0x1000 ; system loaded at 0x10000 (65536).
ENDSEG equ SYSSEG + SYSSIZE ; where to stop loading
; ROOT_DEV: 0x000 - same type of floppy as boot.
; 0x301 - first partition on first drive etc
ROOT_DEV equ 0x306
start:
mov ax,BOOTSEG
mov ds,ax
mov ax,INITSEG
mov es,ax
mov cx,256
sub si,si
sub di,di
rep movsw
jmp INITSEG:go
go: mov ax,cs
mov ds,ax
mov es,ax
; put stack at 0x9ff00.
mov ss,ax
mov sp,0xFF00 ; arbitrary value >>512
; load the setup-sectors directly after the bootblock.
; Note that 'es' is already set up.
load_setup:
mov dx,0x0000 ; drive 0, head 0
mov cx,0x0002 ; sector 2, track 0
mov bx,0x0200 ; address = 512, in INITSEG
mov ax,0x0200+SETUPLEN ; service 2, nr of sectors
int 0x13 ; read it
jnc ok_load_setup ; ok - continue
mov dx,0x0000
mov ax,0x0000 ; reset the diskette
int 0x13
jmp load_setup
ok_load_setup:
; Get disk drive parameters, specifically nr of sectors/track
mov dl,0x00
mov ax,0x0800 ; AH=8 is get drive parameters
int 0x13
mov ch,0x00
mov [cs:sectors],cx
mov ax,INITSEG
mov es,ax
; Print some inane message
mov ah,0x03 ; read cursor pos
xor bh,bh
int 0x10
mov cx,24
mov bx,0x0007 ; page 0, attribute 7 (normal)
mov bp,msg1
mov ax,0x1301 ; write string, move cursor
int 0x10
; ok, we've written the message, now
; we want to load the system (at 0x10000)
mov ax,SYSSEG
mov es,ax ; segment of 0x010000
call read_it
call kill_motor
; After that we check which root-device to use. If the device is
; defined (!= 0), nothing is done and the given device is used.
; Otherwise, either /dev/PS0 (2,28) or /dev/at0 (2,8), depending
; on the number of sectors that the BIOS reports currently.
mov ax,[cs:root_dev]
cmp ax,0
jne root_defined
mov bx,[cs:sectors]
mov ax,0x0208 ; /dev/ps0 - 1.2Mb
cmp bx,15
je root_defined
mov ax,0x021c ; /dev/PS0 - 1.44Mb
cmp bx,18
je root_defined
undef_root:
jmp undef_root
root_defined:
mov [cs:root_dev],ax
; after that (everyting loaded), we jump to
; the setup-routine loaded directly after
; the bootblock:
jmp SETUPSEG:0
; This routine loads the system at address 0x10000, making sure
; no 64kB boundaries are crossed. We try to load it as fast as
; possible, loading whole tracks whenever we can.
;
; in: es - starting address segment (normally 0x1000)
;
sread: dw 1+SETUPLEN ; sectors read of current track
head: dw 0 ; current head
track: dw 0 ; current track
read_it:
mov ax,es
test ax,0x0fff
die: jne die ; es must be at 64kB boundary
xor bx,bx ; bx is starting address within segment
rp_read:
mov ax,es
cmp ax,ENDSEG ; have we loaded all yet?
jb ok1_read
ret
ok1_read:
mov ax,[cs:sectors]
sub ax,sread
mov cx,ax
shl cx,9
add cx,bx
jnc ok2_read
je ok2_read
xor ax,ax
sub ax,bx
shr ax,9
ok2_read:
call read_track
mov cx,ax
add ax,sread
cmp ax,[cs:sectors]
jne ok3_read
mov ax,1
sub ax,head
jne ok4_read
inc word [track]
ok4_read:
mov [head],ax
xor ax,ax
ok3_read:
mov [sread],ax
shl cx,9
add bx,cx
jnc rp_read
mov ax,es
add ax,0x1000
mov es,ax
xor bx,bx
jmp rp_read
read_track:
push ax
push bx
push cx
push dx
mov dx,track
mov cx,sread
inc cx
mov ch,dl
mov dx,head
mov dh,dl
mov dl,0
and dx,0x0100
mov ah,2
int 0x13
jc bad_rt
pop dx
pop cx
pop bx
pop ax
ret
bad_rt: mov ax,0
mov dx,0
int 0x13
pop dx
pop cx
pop bx
pop ax
jmp read_track
; This procedure turns off the floppy drive motor, so
; that we enter the kernel in a known state, and
; don't have to worry about it later.
kill_motor:
push dx
mov dx,0x3f2
mov al,0
out dx, al
pop dx
ret
sectors:
dw 0
msg1:
db 13,10
db "Loading system ..."
db 13,10,13,10
times 508-($-$$) db 0
root_dev:
dw ROOT_DEV
boot_flag:
dw 0xAA55