linux-0.12/boot/setup.S`

setup.S 在进入system前执行，它首先调用bios获得各种硬件参数，然后进入保护模式。

。。代码看起来有点无聊

!
!   setup.s     (C) 1991 Linus Torvalds
!
! setup.s is responsible for getting the system data from the BIOS,
! and putting them into the appropriate places in system memory.
! both setup.s and system has been loaded by the bootblock.
!
! This code asks the bios for memory/disk/other parameters, and
! puts them in a "safe" place: 0x90000-0x901FF, ie where the
! boot-block used to be. It is then up to the protected mode
! system to read them from there before the area is overwritten
! for buffer-blocks.
!

! NOTE! These had better be the same as in bootsect.s!

#include <linux/config.h>
;#define DEF_INITSEG    0x9000
;#define DEF_SYSSEG 0x1000
;#define DEF_SETUPSEG   0x9020
;#define DEF_SYSSIZE    0x3000

INITSEG  = DEF_INITSEG  ! we move boot here - out of the way
SYSSEG   = DEF_SYSSEG   ! system loaded at 0x10000 (65536).
SETUPSEG = DEF_SETUPSEG ! this is the current segment

.globl begtext, begdata, begbss, endtext, enddata, endbss
.text
begtext:
.data
begdata:
.bss
begbss:
.text

entry start
start:

! ok, the read went well so we get current cursor position and save it for
! posterity.

mov ax,#INITSEG ! this is done in bootsect already, but...
mov ds,ax ;0x9000

! Get memory size (extended mem, kB)

mov ah,#0x88
int 0x15
mov [2],ax
;取系统所含扩展内存的大小，保存在0x90002

! check for EGA/VGA and some config parameters

mov ah,#0x12
mov bl,#0x10
int 0x10
mov [8],ax
mov [10],bx  ;0x9000a 安装的显示内存 0x9000b 显示状态（彩色/单色）
mov [12],cx  ;0x9000c 显示卡特性参数

mov ax,#0x5019  ;检查屏幕是否是80*25的
cmp bl,#0x10
je  novga       ;如果中断 返回bl=0x10 表示不是vga显卡 跳 novga
call    chsvga  检测显示卡厂家和类型 修改显示的行列值

novga:  mov [14],ax 保存当前的行列值

;取屏幕当前光标位置
mov ah,#0x03    ! read cursor pos
xor bh,bh
int 0x10        ! save it in known place, con_init fetches
mov [0],dx      ! it from 0x90000.

! Get video-card data:  取显卡当前的显示模式

mov ah,#0x0f
int 0x10
mov [4],bx      ! bh = display page
mov [6],ax      ! al = video mode, ah = window width

! Get hd0 data 取第一个硬盘的信息

mov ax,#0x0000
mov ds,ax
lds si,[4*0x41]
mov ax,#INITSEG
mov es,ax
mov di,#0x0080
mov cx,#0x10
rep
movsb

! Get hd1 data

mov ax,#0x0000
mov ds,ax
lds si,[4*0x46]
mov ax,#INITSEG
mov es,ax
mov di,#0x0090
mov cx,#0x10
rep
movsb

! Check that there IS a hd1 :-) 检查是否有第二个硬盘

mov ax,#0x01500
mov dl,#0x81
int 0x13
jc  no_disk1
cmp ah,#3
je  is_disk1
no_disk1:
mov ax,#INITSEG
mov es,ax
mov di,#0x0090
mov cx,#0x10
mov ax,#0x00
rep
stosb
is_disk1:

! now we want to move to protected mode ... 进入保护模式咯ing

cli         ! no interrupts allowed !

! first we move the system to it's rightful place

mov ax,#0x0000
cld         ! 'direction'=0, movs moves forward
;移动system
do_move:
mov es,ax       ! destination segment
add ax,#0x1000
cmp ax,#0x9000
jz  end_move
mov ds,ax       ! source segment
sub di,di
sub si,si
mov     cx,#0x8000
rep
movsw
jmp do_move

! then we load the segment descriptors

end_move:
mov ax,#SETUPSEG    ! right, forgot this at first. didn't work :-)
mov ds,ax
lidt    idt_48      ! load idt with 0,0
lgdt    gdt_48      ! load gdt with whatever appropriate

! that was painless, now we enable A20

call    empty_8042  ;等待8042状态恢复
mov al,#0xD1        ! command write
out #0x64,al
call    empty_8042
mov al,#0xDF        ! A20 on
out #0x60,al
call    empty_8042

! well, that went ok, I hope. Now we have to reprogram the interrupts :-(
! we put them right after the intel-reserved hardware interrupts, at
! int 0x20-0x2F. There they won't mess up anything. Sadly IBM really
! messed this up with the original PC, and they haven't been able to
! rectify it afterwards. Thus the bios puts interrupts at 0x08-0x0f,
! which is used for the internal hardware interrupts as well. We just
! have to reprogram the 8259's, and it isn't fun.

;重新对8259进行编程
mov al,#0x11        ! initialization sequence
out #0x20,al        ! send it to 8259A-1
.word   0x00eb,0x00eb       ! jmp $+2, jmp $+2
out #0xA0,al        ! and to 8259A-2
.word   0x00eb,0x00eb
mov al,#0x20        ! start of hardware int's (0x20)
out #0x21,al
.word   0x00eb,0x00eb
mov al,#0x28        ! start of hardware int's 2 (0x28)
out #0xA1,al
.word   0x00eb,0x00eb
mov al,#0x04        ! 8259-1 is master
out #0x21,al
.word   0x00eb,0x00eb
mov al,#0x02        ! 8259-2 is slave
out #0xA1,al
.word   0x00eb,0x00eb
mov al,#0x01        ! 8086 mode for both
out #0x21,al
.word   0x00eb,0x00eb
out #0xA1,al
.word   0x00eb,0x00eb
mov al,#0xFF        ! mask off all interrupts for now
out #0x21,al
.word   0x00eb,0x00eb
out #0xA1,al

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;8259 get done
! well, that certainly wasn't fun :-(. Hopefully it works, and we don't
! need no steenking BIOS anyway (except for the initial loading :-).
! The BIOS-routine wants lots of unnecessary data, and it's less
! "interesting" anyway. This is how REAL programmers do it.
!
! Well, now's the time to actually move into protected mode. To make
! things as simple as possible, we do no register set-up or anything,
! we let the gnu-compiled 32-bit programs do that. We just jump to
! absolute address 0x00000, in 32-bit protected mode.

mov ax,#0x0001  ! protected mode (PE) bit
lmsw    ax      ! This is it!    设置cr0 进入到保护模式
jmpi    0,8     ! jmp offset 0 of segment 8 (cs)

;8 =0b 0000 0000 0000 1-000
;所以这里是使用 GDT中的第二个全局描述符
;至此就会跳转执行system中的代码

! This routine checks that the keyboard command queue is empty
! No timeout is used - if this hangs there is something wrong with
! the machine, and we probably couldn't proceed anyway.
empty_8042:
.word   0x00eb,0x00eb
in  al,#0x64    ! 8042 status port
test    al,#2       ! is input buffer full?
jnz empty_8042  ! yes - loop
ret

! Routine trying to recognize type of SVGA-board present (if any)
! and if it recognize one gives the choices of resolution it offers.
! If one is found the resolution chosen is given by al,ah (rows,cols).

chsvga: cld
push    ds
push    cs
pop ds
mov     ax,#0xc000
mov es,ax
lea si,msg1
call    prtstr
nokey:  in  al,#0x60
cmp al,#0x82
jb  nokey
cmp al,#0xe0
ja  nokey
cmp al,#0x9c
je  svga
mov ax,#0x5019
pop ds
ret
svga:   lea     si,idati        ! Check ATI 'clues'
mov di,#0x31
mov     cx,#0x09
repe
cmpsb
jne noati
lea si,dscati
lea di,moati
lea cx,selmod
jmp cx
noati:  mov ax,#0x200f      ! Check Ahead 'clues'
mov dx,#0x3ce
out dx,ax
inc dx
in  al,dx
cmp al,#0x20
je  isahed
cmp al,#0x21
jne noahed
isahed: lea si,dscahead
lea di,moahead
lea cx,selmod
jmp cx
noahed: mov dx,#0x3c3       ! Check Chips & Tech. 'clues'
in  al,dx
or  al,#0x10
out dx,al
mov dx,#0x104
in  al,dx
mov bl,al
mov dx,#0x3c3
in  al,dx
and al,#0xef
out dx,al
cmp bl,[idcandt]
jne nocant
lea si,dsccandt
lea di,mocandt
lea cx,selmod
jmp cx
nocant: mov dx,#0x3d4       ! Check Cirrus 'clues'
mov al,#0x0c
out dx,al
inc dx
in  al,dx
mov bl,al
xor al,al
out dx,al
dec dx
mov al,#0x1f
out dx,al
inc dx
in  al,dx
mov bh,al
xor ah,ah
shl al,#4
mov cx,ax
mov al,bh
shr al,#4
add cx,ax
shl cx,#8
add cx,#6
mov ax,cx
mov dx,#0x3c4
out dx,ax
inc dx
in  al,dx
and al,al
jnz nocirr
mov al,bh
out dx,al
in  al,dx
cmp al,#0x01
jne nocirr
call    rst3d4
lea si,dsccirrus
lea di,mocirrus
lea cx,selmod
jmp cx
rst3d4: mov dx,#0x3d4
mov al,bl
xor ah,ah
shl ax,#8
add ax,#0x0c
out dx,ax
ret
nocirr: call    rst3d4          ! Check Everex 'clues'
mov ax,#0x7000
xor bx,bx
int 0x10
cmp al,#0x70
jne noevrx
shr dx,#4
cmp dx,#0x678
je  istrid
cmp dx,#0x236
je  istrid
lea si,dsceverex
lea di,moeverex
lea cx,selmod
jmp cx
istrid: lea cx,ev2tri
jmp cx
noevrx: lea si,idgenoa      ! Check Genoa 'clues'
xor     ax,ax
seg es
mov al,[0x37]
mov di,ax
mov cx,#0x04
dec si
dec di
l1: inc si
inc di
mov al,(si)
seg es
and al,(di)
cmp al,(si)
loope   l1
cmp cx,#0x00
jne nogen
lea si,dscgenoa
lea di,mogenoa
lea cx,selmod
jmp cx
nogen:  lea si,idparadise       ! Check Paradise 'clues'
mov di,#0x7d
mov cx,#0x04
repe
cmpsb
jne nopara
lea si,dscparadise
lea di,moparadise
lea cx,selmod
jmp cx
nopara: mov dx,#0x3c4       ! Check Trident 'clues'
mov al,#0x0e
out dx,al
inc dx
in  al,dx
xchg    ah,al
mov al,#0x00
out dx,al
in  al,dx
xchg    al,ah
mov bl,al       ! Strange thing ... in the book this wasn't
and bl,#0x02    ! necessary but it worked on my card which
jz  setb2       ! is a trident. Without it the screen goes
and al,#0xfd    ! blurred ...
jmp clrb2       !
setb2:  or  al,#0x02    !
clrb2:  out dx,al
and ah,#0x0f
cmp ah,#0x02
jne notrid
ev2tri: lea si,dsctrident
lea di,motrident
lea cx,selmod
jmp cx
notrid: mov dx,#0x3cd       ! Check Tseng 'clues'
in  al,dx           ! Could things be this simple ! :-)
mov bl,al
mov al,#0x55
out dx,al
in  al,dx
mov ah,al
mov al,bl
out dx,al
cmp ah,#0x55
jne notsen
lea si,dsctseng
lea di,motseng
lea cx,selmod
jmp cx
notsen: mov dx,#0x3cc       ! Check Video7 'clues'
in  al,dx
mov dx,#0x3b4
and al,#0x01
jz  even7
mov dx,#0x3d4
even7:  mov al,#0x0c
out dx,al
inc dx
in  al,dx
mov bl,al
mov al,#0x55
out dx,al
in  al,dx
dec dx
mov al,#0x1f
out dx,al
inc dx
in  al,dx
mov bh,al
dec dx
mov al,#0x0c
out dx,al
inc dx
mov al,bl
out dx,al
mov al,#0x55
xor al,#0xea
cmp al,bh
jne novid7
lea si,dscvideo7
lea di,movideo7
selmod: push    si
lea si,msg2
call    prtstr
xor cx,cx
mov cl,(di)
pop si
push    si
push    cx
tbl:    pop bx
push    bx
mov al,bl
sub al,cl
call    dprnt
call    spcing
lodsw
xchg    al,ah
call    dprnt
xchg    ah,al
push    ax
mov al,#0x78
call    prnt1
pop ax
call    dprnt
call    docr
loop    tbl
pop cx
call    docr
lea si,msg3
call    prtstr
pop si
add cl,#0x80
nonum:  in  al,#0x60    ! Quick and dirty...
cmp al,#0x82
jb  nonum
cmp al,#0x8b
je  zero
cmp al,cl
ja  nonum
jmp nozero
zero:   sub al,#0x0a
nozero: sub al,#0x80
dec al
xor ah,ah
add di,ax
inc di
push    ax
mov al,(di)
int     0x10
pop ax
shl ax,#1
add si,ax
lodsw
pop ds
ret
novid7: pop ds  ! Here could be code to support standard 80x50,80x30
mov ax,#0x5019
ret

! Routine that 'tabs' to next col.

spcing: mov al,#0x2e
call    prnt1
mov al,#0x20
call    prnt1
mov al,#0x20
call    prnt1
mov al,#0x20
call    prnt1
mov al,#0x20
call    prnt1
ret

! Routine to print asciiz-string at DS:SI

prtstr: lodsb
and al,al
jz  fin
call    prnt1
jmp prtstr
fin:    ret

! Routine to print a decimal value on screen, the value to be
! printed is put in al (i.e 0-255).

dprnt:  push    ax
push    cx
mov ah,#0x00
mov cl,#0x0a
idiv    cl
cmp al,#0x09
jbe lt100
call    dprnt
jmp skip10
lt100:  add al,#0x30
call    prnt1
skip10: mov al,ah
add al,#0x30
call    prnt1
pop cx
pop ax
ret

! Part of above routine, this one just prints ascii al

prnt1:  push    ax
push    cx
mov bh,#0x00
mov cx,#0x01
mov ah,#0x0e
int 0x10
pop cx
pop ax
ret

! Prints <CR> + <LF>

docr:   push    ax
push    cx
mov bh,#0x00
mov ah,#0x0e
mov al,#0x0a
mov cx,#0x01
int 0x10
mov al,#0x0d
int 0x10
pop cx
pop ax
ret

gdt:
.word   0,0,0,0     ! dummy

.word   0x07FF      ! 8Mb - limit=2047 (2048*4096=8Mb)
.word   0x0000      ! base address=0
.word   0x9A00      ! code read/exec
.word   0x00C0      ! granularity=4096, 386

.word   0x07FF      ! 8Mb - limit=2047 (2048*4096=8Mb)
.word   0x0000      ! base address=0
.word   0x9200      ! data read/write
.word   0x00C0      ! granularity=4096, 386

idt_48:
.word   0           ! idt limit=0
.word   0,0         ! idt base=0L

gdt_48:
.word   0x800       ! gdt limit=2048, 256 GDT entries
.word   512+gdt,0x9 ! gdt base = 0X9xxxx

msg1:       .ascii  "Press <RETURN> to see SVGA-modes available or any other key to continue."
db  0x0d, 0x0a, 0x0a, 0x00
msg2:       .ascii  "Mode:  COLSxROWS:"
db  0x0d, 0x0a, 0x0a, 0x00
msg3:       .ascii  "Choose mode by pressing the corresponding number."
db  0x0d, 0x0a, 0x00

idati:      .ascii  "761295520"
idcandt:    .byte   0xa5
idgenoa:    .byte   0x77, 0x00, 0x66, 0x99
idparadise: .ascii  "VGA="

! Manufacturer:   Numofmodes:   Mode:

moati:      .byte   0x02,   0x23, 0x33
moahead:    .byte   0x05,   0x22, 0x23, 0x24, 0x2f, 0x34
mocandt:    .byte   0x02,   0x60, 0x61
mocirrus:   .byte   0x04,   0x1f, 0x20, 0x22, 0x31
moeverex:   .byte   0x0a,   0x03, 0x04, 0x07, 0x08, 0x0a, 0x0b, 0x16, 0x18, 0x21, 0x40
mogenoa:    .byte   0x0a,   0x58, 0x5a, 0x60, 0x61, 0x62, 0x63, 0x64, 0x72, 0x74, 0x78
moparadise: .byte   0x02,   0x55, 0x54
motrident:  .byte   0x07,   0x50, 0x51, 0x52, 0x57, 0x58, 0x59, 0x5a
motseng:    .byte   0x05,   0x26, 0x2a, 0x23, 0x24, 0x22
movideo7:   .byte   0x06,   0x40, 0x43, 0x44, 0x41, 0x42, 0x45

!           msb = Cols lsb = Rows:

dscati:     .word   0x8419, 0x842c
dscahead:   .word   0x842c, 0x8419, 0x841c, 0xa032, 0x5042
dsccandt:   .word   0x8419, 0x8432
dsccirrus:  .word   0x8419, 0x842c, 0x841e, 0x6425
dsceverex:  .word   0x5022, 0x503c, 0x642b, 0x644b, 0x8419, 0x842c, 0x501e, 0x641b, 0xa040, 0x841e
dscgenoa:   .word   0x5020, 0x642a, 0x8419, 0x841d, 0x8420, 0x842c, 0x843c, 0x503c, 0x5042, 0x644b
dscparadise:    .word   0x8419, 0x842b
dsctrident: .word   0x501e, 0x502b, 0x503c, 0x8419, 0x841e, 0x842b, 0x843c
dsctseng:   .word   0x503c, 0x6428, 0x8419, 0x841c, 0x842c
dscvideo7:  .word   0x502b, 0x503c, 0x643c, 0x8419, 0x842c, 0x841c

.text
endtext:
.data
enddata:
.bss
endbss:

当setup执行后，system模块被移动到0x0000开始处，而从0x90000开始存放了内核会使用的系统基本参数。

此时临时全局描述表中有三个描述符：第一个是NULL不使用，另外两个是代码段描述符和数据段描述符，他们都指向系统模块的起始处，0x0000，最后一句jmpi 0,8 会跳转到system模块的开始部分，也就是head.s 继续执行下去；