《一个64位系统的设计与实现》－－BootLoader(2)
一、在boot文件中添加文件加载功能
在上一篇文章中介绍了如何制作一个简单的boot引导程序，这篇文章在此基础上加上文件加载的功能，实现完整的Boot引导功能。
本系统使用逻辑简单的FAT12文件系统来装载Loader程序和内核程序，在boot中添加FAT12文件系统的信息。具体的理论知识参考书，这里直接贴上代码和操作步骤。
将上一篇文章中的boot.asm文件用下面这段代码替代，并重新执行之后的步骤。
org 0x7c00
BaseOfStack equ 0x7c00
BaseOfLoader equ 0x1000
OffsetOfLoader equ 0x00
RootDirSectors equ 14
SectorNumOfRootDirStart equ 19
SectorNumOfFAT1Start equ 1
SectorBalance equ 17
jmp short Label_Start
nop
BS_OEMName db 'MINEboot'
BPB_BytesPerSec dw 512
BPB_SecPerClus db 1
BPB_RsvdSecCnt dw 1
BPB_NumFATs db 2
BPB_RootEntCnt dw 224
BPB_TotSec16 dw 2880
BPB_Media db 0xf0
BPB_FATSz16 dw 9
BPB_SecPerTrk dw 18
BPB_NumHeads dw 2
BPB_HiddSec dd 0
BPB_TotSec32 dd 0
BS_DrvNum db 0
BS_Reserved1 db 0
BS_BootSig db 0x29
BS_VolID dd 0
BS_VolLab db 'boot loader'
BS_FileSysType db 'FAT12 '
Label_Start:
mov ax, cs
mov ds, ax
mov es, ax
mov ss, ax
mov sp, BaseOfStack
;======= clear screen
mov ax, 0600h
mov bx, 0700h
mov cx, 0
mov dx, 0184fh
int 10h
;======= set focus
mov ax, 0200h
mov bx, 0000h
mov dx, 0000h
int 10h
;======= display on screen : Start Booting......
mov ax, 1301h
mov bx, 000fh
mov dx, 0000h
mov cx, 10
push ax
mov ax, ds
mov es, ax
pop ax
mov bp, StartBootMessage
int 10h
;======= reset floppy
xor ah, ah
xor dl, dl
int 13h
;======= search loader.bin
mov word [SectorNo], SectorNumOfRootDirStart
Lable_Search_In_Root_Dir_Begin:
cmp word [RootDirSizeForLoop], 0
jz Label_No_LoaderBin
dec word [RootDirSizeForLoop]
mov ax, 00h
mov es, ax
mov bx, 8000h
mov ax, [SectorNo]
mov cl, 1
call Func_ReadOneSector
mov si, LoaderFileName
mov di, 8000h
cld
mov dx, 10h
Label_Search_For_LoaderBin:
cmp dx, 0
jz Label_Goto_Next_Sector_In_Root_Dir
dec dx
mov cx, 11
Label_Cmp_FileName:
cmp cx, 0
jz Label_FileName_Found
dec cx
lodsb
cmp al, byte [es:di]
jz Label_Go_On
jmp Label_Different
Label_Go_On:
inc di
jmp Label_Cmp_FileName
Label_Different:
and di, 0ffe0h
add di, 20h
mov si, LoaderFileName
jmp Label_Search_For_LoaderBin
Label_Goto_Next_Sector_In_Root_Dir:
add word [SectorNo], 1
jmp Lable_Search_In_Root_Dir_Begin
;======= display on screen : ERROR:No LOADER Found
Label_No_LoaderBin:
mov ax, 1301h
mov bx, 008ch
mov dx, 0100h
mov cx, 21
push ax
mov ax, ds
mov es, ax
pop ax
mov bp, NoLoaderMessage
int 10h
jmp BaseOfLoader:OffsetOfLoader
;======= found loader.bin name in root director struct
Label_FileName_Found:
mov ax, RootDirSectors
and di, 0ffe0h
add di, 01ah
mov cx, word [es:di]
push cx
add cx, ax
add cx, SectorBalance
mov ax, BaseOfLoader
mov es, ax
mov bx, OffsetOfLoader
mov ax, cx
Label_Go_On_Loading_File:
push ax
push bx
mov ah, 0eh
mov al, '.'
mov bl, 0fh
int 10h
pop bx
pop ax
mov cl, 1
call Func_ReadOneSector
pop ax
call Func_GetFATEntry
cmp ax, 0fffh
jz Label_File_Loaded
push ax
mov dx, RootDirSectors
add ax, dx
add ax, SectorBalance
add bx, [BPB_BytesPerSec]
jmp Label_Go_On_Loading_File
Label_File_Loaded:
jmp BaseOfLoader:OffsetOfLoader
;======= read one sector from floppy
Func_ReadOneSector:
push bp
mov bp, sp
sub esp, 2
mov byte [bp - 2], cl
push bx
mov bl, [BPB_SecPerTrk]
div bl
inc ah
mov cl, ah
mov dh, al
shr al, 1
mov ch, al
and dh, 1
pop bx
mov dl, [BS_DrvNum]
Label_Go_On_Reading:
mov ah, 2
mov al, byte [bp - 2]
int 13h
jc Label_Go_On_Reading
add esp, 2
pop bp
ret
;======= get FAT Entry
Func_GetFATEntry:
push es
push bx
push ax
mov ax, 00
mov es, ax
pop ax
mov byte [Odd], 0
mov bx, 3
mul bx
mov bx, 2
div bx
cmp dx, 0
jz Label_Even
mov byte [Odd], 1
Label_Even:
xor dx, dx
mov bx, [BPB_BytesPerSec]
div bx
push dx
mov bx, 8000h
add ax, SectorNumOfFAT1Start
mov cl, 2
call Func_ReadOneSector
pop dx
add bx, dx
mov ax, [es:bx]
cmp byte [Odd], 1
jnz Label_Even_2
shr ax, 4
Label_Even_2:
and ax, 0fffh
pop bx
pop es
ret
;======= tmp variable
RootDirSizeForLoop dw RootDirSectors
SectorNo dw 0
Odd db 0
;======= display messages
StartBootMessage: db "Start Boot"
NoLoaderMessage: db "ERROR:No LOADER Found"
LoaderFileName: db "LOADER BIN",0
;======= fill zero until whole sector
times 510 - ($ - $$) db 0
dw 0xaa55
二、制作loder文件
Loader引导加载程序负责①检测硬件信息 ②处理器模式切换 ③向内核传递数据 三部分工作。
首先，新建一个文件，命名为loader.asm，代码内容如下：
org 10000h
jmp Label_Start
%include "fat12.inc"
BaseOfKernelFile equ 0x00
OffsetOfKernelFile equ 0x100000
BaseTmpOfKernelAddr equ 0x00
OffsetTmpOfKernelFile equ 0x7E00
MemoryStructBufferAddr equ 0x7E00
[SECTION gdt]
LABEL_GDT: dd 0,0
LABEL_DESC_CODE32: dd 0x0000FFFF,0x00CF9A00
LABEL_DESC_DATA32: dd 0x0000FFFF,0x00CF9200
GdtLen equ $ - LABEL_GDT
GdtPtr dw GdtLen - 1
dd LABEL_GDT
SelectorCode32 equ LABEL_DESC_CODE32 - LABEL_GDT
SelectorData32 equ LABEL_DESC_DATA32 - LABEL_GDT
[SECTION gdt64]
LABEL_GDT64: dq 0x0000000000000000
LABEL_DESC_CODE64: dq 0x0020980000000000
LABEL_DESC_DATA64: dq 0x0000920000000000
GdtLen64 equ $ - LABEL_GDT64
GdtPtr64 dw GdtLen64 - 1
dd LABEL_GDT64
SelectorCode64 equ LABEL_DESC_CODE64 - LABEL_GDT64
SelectorData64 equ LABEL_DESC_DATA64 - LABEL_GDT64
[SECTION .s16]
[BITS 16]
Label_Start:
mov ax, cs
mov ds, ax
mov es, ax
mov ax, 0x00
mov ss, ax
mov sp, 0x7c00
;======= display on screen : Start Loader......
mov ax, 1301h
mov bx, 000fh
mov dx, 0200h ;row 2
mov cx, 12
push ax
mov ax, ds
mov es, ax
pop ax
mov bp, StartLoaderMessage
int 10h
;======= open address A20
push ax
in al, 92h
or al, 00000010b
out 92h, al
pop ax
cli
db 0x66
lgdt [GdtPtr]
mov eax, cr0
or eax, 1
mov cr0, eax
mov ax, SelectorData32
mov fs, ax
mov eax, cr0
and al, 11111110b
mov cr0, eax
sti
;======= reset floppy
xor ah, ah
xor dl, dl
int 13h
;======= search kernel.bin
mov word [SectorNo], SectorNumOfRootDirStart
Lable_Search_In_Root_Dir_Begin:
cmp word [RootDirSizeForLoop], 0
jz Label_No_LoaderBin
dec word [RootDirSizeForLoop]
mov ax, 00h
mov es, ax
mov bx, 8000h
mov ax, [SectorNo]
mov cl, 1
call Func_ReadOneSector
mov si, KernelFileName
mov di, 8000h
cld
mov dx, 10h
Label_Search_For_LoaderBin:
cmp dx, 0
jz Label_Goto_Next_Sector_In_Root_Dir
dec dx
mov cx, 11
Label_Cmp_FileName:
cmp cx, 0
jz Label_FileName_Found
dec cx
lodsb
cmp al, byte [es:di]
jz Label_Go_On
jmp Label_Different
Label_Go_On:
inc di
jmp Label_Cmp_FileName
Label_Different:
and di, 0FFE0h
add di, 20h
mov si, KernelFileName
jmp Label_Search_For_LoaderBin
Label_Goto_Next_Sector_In_Root_Dir:
add word [SectorNo], 1
jmp Lable_Search_In_Root_Dir_Begin
;======= display on screen : ERROR:No KERNEL Found
Label_No_LoaderBin:
mov ax, 1301h
mov bx, 008Ch
mov dx, 0300h ;row 3
mov cx, 21
push ax
mov ax, ds
mov es, ax
pop ax
mov bp, NoLoaderMessage
int 10h
jmp $
;======= found loader.bin name in root director struct
Label_FileName_Found:
mov ax, RootDirSectors
and di, 0FFE0h
add di, 01Ah
mov cx, word [es:di]
push cx
add cx, ax
add cx, SectorBalance
mov eax, BaseTmpOfKernelAddr ;BaseOfKernelFile
mov es, eax
mov bx, OffsetTmpOfKernelFile ;OffsetOfKernelFile
mov ax, cx
Label_Go_On_Loading_File:
push ax
push bx
mov ah, 0Eh
mov al, '.'
mov bl, 0Fh
int 10h
pop bx
pop ax
mov cl, 1
call Func_ReadOneSector
pop ax
;;;;;;;;;;;;;;;;;;;;;;;
push cx
push eax
push fs
push edi
push ds
push esi
mov cx, 200h
mov ax, BaseOfKernelFile
mov fs, ax
mov edi, dword [OffsetOfKernelFileCount]
mov ax, BaseTmpOfKernelAddr
mov ds, ax
mov esi, OffsetTmpOfKernelFile
Label_Mov_Kernel: ;------------------
mov al, byte [ds:esi]
mov byte [fs:edi], al
inc esi
inc edi
loop Label_Mov_Kernel
mov eax, 0x1000
mov ds, eax
mov dword [OffsetOfKernelFileCount], edi
pop esi
pop ds
pop edi
pop fs
pop eax
pop cx
;;;;;;;;;;;;;;;;;;;;;;;
call Func_GetFATEntry
cmp ax, 0FFFh
jz Label_File_Loaded
push ax
mov dx, RootDirSectors
add ax, dx
add ax, SectorBalance
jmp Label_Go_On_Loading_File
Label_File_Loaded:
mov ax, 0B800h
mov gs, ax
mov ah, 0Fh ; 0000: 黑底 1111: 白字
mov al, 'G'
mov [gs:((80 * 0 + 39) * 2)], ax ; 屏幕第 0 行, 第 39 列。
KillMotor:
push dx
mov dx, 03F2h
mov al, 0
out dx, al
pop dx
;======= get memory address size type
mov ax, 1301h
mov bx, 000Fh
mov dx, 0400h ;row 4
mov cx, 24
push ax
mov ax, ds
mov es, ax
pop ax
mov bp, StartGetMemStructMessage
int 10h
mov ebx, 0
mov ax, 0x00
mov es, ax
mov di, MemoryStructBufferAddr
Label_Get_Mem_Struct:
mov eax, 0x0E820
mov ecx, 20
mov edx, 0x534D4150
int 15h
jc Label_Get_Mem_Fail
add di, 20
cmp ebx, 0
jne Label_Get_Mem_Struct
jmp Label_Get_Mem_OK
Label_Get_Mem_Fail:
mov ax, 1301h
mov bx, 008Ch
mov dx, 0500h ;row 5
mov cx, 23
push ax
mov ax, ds
mov es, ax
pop ax
mov bp, GetMemStructErrMessage
int 10h
jmp $
Label_Get_Mem_OK:
mov ax, 1301h
mov bx, 000Fh
mov dx, 0600h ;row 6
mov cx, 29
push ax
mov ax, ds
mov es, ax
pop ax
mov bp, GetMemStructOKMessage
int 10h
;======= get SVGA information
mov ax, 1301h
mov bx, 000Fh
mov dx, 0800h ;row 8
mov cx, 23
push ax
mov ax, ds
mov es, ax
pop ax
mov bp, StartGetSVGAVBEInfoMessage
int 10h
mov ax, 0x00
mov es, ax
mov di, 0x8000
mov ax, 4F00h
int 10h
cmp ax, 004Fh
jz .KO
;======= Fail
mov ax, 1301h
mov bx, 008Ch
mov dx, 0900h ;row 9
mov cx, 23
push ax
mov ax, ds
mov es, ax
pop ax
mov bp, GetSVGAVBEInfoErrMessage
int 10h
jmp $
.KO:
mov ax, 1301h
mov bx, 000Fh
mov dx, 0A00h ;row 10
mov cx, 29
push ax
mov ax, ds
mov es, ax
pop ax
mov bp, GetSVGAVBEInfoOKMessage
int 10h
;======= Get SVGA Mode Info
mov ax, 1301h
mov bx, 000Fh
mov dx, 0C00h ;row 12
mov cx, 24
push ax
mov ax, ds
mov es, ax
pop ax
mov bp, StartGetSVGAModeInfoMessage
int 10h
mov ax, 0x00
mov es, ax
mov si, 0x800e
mov esi, dword [es:si]
mov edi, 0x8200
Label_SVGA_Mode_Info_Get:
mov cx, word [es:esi]
;======= display SVGA mode information
push ax
mov ax, 00h
mov al, ch
call Label_DispAL
mov ax, 00h
mov al, cl
call Label_DispAL
pop ax
;=======
cmp cx, 0FFFFh
jz Label_SVGA_Mode_Info_Finish
mov ax, 4F01h
int 10h
cmp ax, 004Fh
jnz Label_SVGA_Mode_Info_FAIL
add esi, 2
add edi, 0x100
jmp Label_SVGA_Mode_Info_Get
Label_SVGA_Mode_Info_FAIL:
mov ax, 1301h
mov bx, 008Ch
mov dx, 0D00h ;row 13
mov cx, 24
push ax
mov ax, ds
mov es, ax
pop ax
mov bp, GetSVGAModeInfoErrMessage
int 10h
Label_SET_SVGA_Mode_VESA_VBE_FAIL:
jmp $
Label_SVGA_Mode_Info_Finish:
mov ax, 1301h
mov bx, 000Fh
mov dx, 0E00h ;row 14
mov cx, 30
push ax
mov ax, ds
mov es, ax
pop ax
mov bp, GetSVGAModeInfoOKMessage
int 10h
;======= set the SVGA mode(VESA VBE)
mov ax, 4F02h
mov bx, 4180h ;========================mode : 0x180 or 0x143
int 10h
cmp ax, 004Fh
jnz Label_SET_SVGA_Mode_VESA_VBE_FAIL
;======= init IDT GDT goto protect mode
cli ;======close interrupt
db 0x66
lgdt [GdtPtr]
; db 0x66
; lidt [IDT_POINTER]
mov eax, cr0
or eax, 1
mov cr0, eax
jmp dword SelectorCode32:GO_TO_TMP_Protect
[SECTION .s32]
[BITS 32]
GO_TO_TMP_Protect:
;======= go to tmp long mode
mov ax, 0x10
mov ds, ax
mov es, ax
mov fs, ax
mov ss, ax
mov esp, 7E00h
call support_long_mode
test eax, eax
jz no_support
;======= init temporary page table 0x90000
mov dword [0x90000], 0x91007
mov dword [0x90800], 0x91007
mov dword [0x91000], 0x92007
mov dword [0x92000], 0x000083
mov dword [0x92008], 0x200083
mov dword [0x92010], 0x400083
mov dword [0x92018], 0x600083
mov dword [0x92020], 0x800083
mov dword [0x92028], 0xa00083
;======= load GDTR
db 0x66
lgdt [GdtPtr64]
mov ax, 0x10
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
mov ss, ax
mov esp, 7E00h
;======= open PAE
mov eax, cr4
bts eax, 5
mov cr4, eax
;======= load cr3
mov eax, 0x90000
mov cr3, eax
;======= enable long-mode
mov ecx, 0C0000080h ;IA32_EFER
rdmsr
bts eax, 8
wrmsr
;======= open PE and paging
mov eax, cr0
bts eax, 0
bts eax, 31
mov cr0, eax
jmp SelectorCode64:OffsetOfKernelFile
;======= test support long mode or not
support_long_mode:
mov eax, 0x80000000
cpuid
cmp eax, 0x80000001
setnb al
jb support_long_mode_done
mov eax, 0x80000001
cpuid
bt edx, 29
setc al
support_long_mode_done:
movzx eax, al
ret
;======= no support
no_support:
jmp $
;======= read one sector from floppy
[SECTION .s16lib]
[BITS 16]
Func_ReadOneSector:
push bp
mov bp, sp
sub esp, 2
mov byte [bp - 2], cl
push bx
mov bl, [BPB_SecPerTrk]
div bl
inc ah
mov cl, ah
mov dh, al
shr al, 1
mov ch, al
and dh, 1
pop bx
mov dl, [BS_DrvNum]
Label_Go_On_Reading:
mov ah, 2
mov al, byte [bp - 2]
int 13h
jc Label_Go_On_Reading
add esp, 2
pop bp
ret
;======= get FAT Entry
Func_GetFATEntry:
push es
push bx
push ax
mov ax, 00
mov es, ax
pop ax
mov byte [Odd], 0
mov bx, 3
mul bx
mov bx, 2
div bx
cmp dx, 0
jz Label_Even
mov byte [Odd], 1
Label_Even:
xor dx, dx
mov bx, [BPB_BytesPerSec]
div bx
push dx
mov bx, 8000h
add ax, SectorNumOfFAT1Start
mov cl, 2
call Func_ReadOneSector
pop dx
add bx, dx
mov ax, [es:bx]
cmp byte [Odd], 1
jnz Label_Even_2
shr ax, 4
Label_Even_2:
and ax, 0FFFh
pop bx
pop es
ret
;======= display num in al
Label_DispAL:
push ecx
push edx
push edi
mov edi, [DisplayPosition]
mov ah, 0Fh
mov dl, al
shr al, 4
mov ecx, 2
.begin:
and al, 0Fh
cmp al, 9
ja .1
add al, '0'
jmp .2
.1:
sub al, 0Ah
add al, 'A'
.2:
mov [gs:edi], ax
add edi, 2
mov al, dl
loop .begin
mov [DisplayPosition], edi
pop edi
pop edx
pop ecx
ret
;======= tmp IDT
IDT:
times 0x50 dq 0
IDT_END:
IDT_POINTER:
dw IDT_END - IDT - 1
dd IDT
;======= tmp variable
RootDirSizeForLoop dw RootDirSectors
SectorNo dw 0
Odd db 0
OffsetOfKernelFileCount dd OffsetOfKernelFile
DisplayPosition dd 0
;======= display messages
StartLoaderMessage: db "Start Loader"
NoLoaderMessage: db "ERROR:No KERNEL Found"
KernelFileName: db "KERNEL BIN",0
StartGetMemStructMessage: db "Start Get Memory Struct."
GetMemStructErrMessage: db "Get Memory Struct ERROR"
GetMemStructOKMessage: db "Get Memory Struct SUCCESSFUL!"
StartGetSVGAVBEInfoMessage: db "Start Get SVGA VBE Info"
GetSVGAVBEInfoErrMessage: db "Get SVGA VBE Info ERROR"
GetSVGAVBEInfoOKMessage: db "Get SVGA VBE Info SUCCESSFUL!"
StartGetSVGAModeInfoMessage: db "Start Get SVGA Mode Info"
GetSVGAModeInfoErrMessage: db "Get SVGA Mode Info ERROR"
GetSVGAModeInfoOKMessage: db "Get SVGA Mode Info SUCCESSFUL!"
该段程序中加载了一个fat12.inc的文件，该文件包含了FAT12系统的基本信息。在loader.asm同一路径下新建一个文件fat12.inc，文件内容如下。
RootDirSectors equ 14
SectorNumOfRootDirStart equ 19
SectorNumOfFAT1Start equ 1
SectorBalance equ 17
BS_OEMName db 'MINEboot'
BPB_BytesPerSec dw 512
BPB_SecPerClus db 1
BPB_RsvdSecCnt dw 1
BPB_NumFATs db 2
BPB_RootEntCnt dw 224
BPB_TotSec16 dw 2880
BPB_Media db 0xf0
BPB_FATSz16 dw 9
BPB_SecPerTrk dw 18
BPB_NumHeads dw 2
BPB_hiddSec dd 0
BPB_TotSec32 dd 0
BS_DrvNum db 0
BS_Reserved1 db 0
BS_BootSig db 29h
BS_VolID dd 0
BS_VolLab db 'boot loader'
BS_FileSysType db 'FAT12 '
之后编译loader.asm文件，编译命令为： nasm loader.asm -o loader.bin
编译结束后，将生成的二进制程序loader.bin 复制到虚拟软盘镜像文件boot.img中。由于此时的boot.img已经有了FAT12文件系统，所以现在可以使用挂载文件系统的方式将loader.bin 复制到文件系统中 。依次执行：
mount (bochs路径)/boot.img /media/ -t vfat -o loop
cp loader.bin /media/
sync
umount /media/执行之后，即可如上一篇中所述运行bochs，运行后界面如下，由于现在还没有转到内核中，会显示找不到内核文件的错误。
