我将自举程序从CHS更改为LBA,因此我将int 13h 02h
替换为int 13h 42h
。它在QEMU中正常工作,但是,我在使用Bochs和笔记本电脑时遇到了麻烦。
我使用dd if=main.bin of=/dev/sdb bs=512
将bootloader写入USB闪存盘。笔记本电脑加载Intel UNDI并给我以下错误:No bootable device - insert boot disk and press any key
。
所以我尝试用Bochs调试它,并注意到Bochs将这个二进制文件识别为可引导的。但是,int 13h
执行后没有加载任何内容。
然后我尝试从这个闪存驱动器加载我的旧PC,它的工作原理!它加载程序并正确执行它。 QEMU给了我相同的结果。
以下是引导加载程序代码:
org 0x7c00
bits 16
boot:
cli
; Overlap CS and DS
mov ax, cs
mov ds, ax
mov es, ax
; Setup 4K stack before this bootloader
mov ax, 0x07c0
mov ss, ax
mov sp, 4096
; Load next sectors
mov si, DAP
mov ah, 42h
; DL didn't changed
int 13h
; Start
jmp bootend
; Disk address packet
DAP:
db 10h, 0
dw %1 ; Number of sectors to be loaded
dd bootend
dq 1
; Fill the rest of bootsector with zeroes and end it
times 510 - ($ - boot) db 0
dw 0xAA55
bootend:
bochsrc:
megs: 32
romimage: file=/usr/share/bochs/BIOS-bochs-latest, address=0xfffe0000
vgaromimage: file=/usr/share/bochs/VGABIOS-lgpl-latest
floppya: 1_44=main.bin, status=inserted
boot: a
panic: action=ask
log: bochsout.txt
mouse: enabled=0
keyboard: type=mf, serial_delay=200, paste_delay=100000
display_library: x, options="gui_debug"
答案 0 :(得分:7)
并非所有BIOS都支持扩展磁盘读写功能(尽管在现代硬件上它们几乎都可能)。并非所有BIOS都支持通过Int 13h/AH=42h扩展磁盘读取软盘。对于 BOCHS 也是如此。您可以通过Int 13/AH=41h/BX=55AAh测试驱动器上的扩展磁盘功能是否可用。这会进行扩展磁盘安装检查。
如果要使用扩展磁盘读取和LBA在 BOCHS 上测试代码,则必须创建硬盘映像并修改 BOCHS 以从中启动而不是软盘。 BOCHS 支持的最小硬盘映像大小为CHS = 1/16/63,即512 * 16 * 63 = 516096字节或1008个扇区,每个512字节。
您可以将bochsrc.txt
修改为:
megs: 32
romimage: file=/usr/share/bochs/BIOS-bochs-latest, address=0xfffe0000
vgaromimage: file=/usr/share/bochs/VGABIOS-lgpl-latest
boot: c
ata0: enabled=1, ioaddr1=0x1f0, ioaddr2=0x3f0, irq=14
ata0-master: type=disk, path="disk.img", mode=flat, cylinders=0, heads=0, spt=0, model="Generic 1234", biosdetect=auto, translation=auto
panic: action=ask
log: bochsout.txt
mouse: enabled=0
keyboard: type=mf, serial_delay=200, paste_delay=100000
display_library: x, options="gui_debug"
我使用名为disk.img
的磁盘映像。您可以使用以下命令创建它并将生成的扇区放入其中:
nasm -f bin main.asm -o main.bin
创建516096字节的图像:
dd if=/dev/zero of=disk.img count=1008 bs=512
将引导扇区放在disk.img
的开头,而不截断文件:
dd if=main.bin of=disk.img conv=notrunc
我有关于使用 DD 在此Stackoverflow answer中创建磁盘映像的其他信息。
虽然磁盘映像是 BOCHS 问题的一部分,但您确实遇到了一些编码问题。您不能假设 CS 的值将设置为当您将控制权从BIOS传输到引导加载程序时的想法。有关详细信息,请参阅我的General Bootloader Tips。如果您希望 DS 和 ES 为零(这是org 0x7c00
所需要的),则应将代码的开头修改为是这样的:
org 0x7c00
bits 16
boot:
cli
xor ax, ax ; Explicitly set DS and ES to 0
mov ds, ax
mov es, ax
为了测试您的代码,我在bootend
:
bootend:
; Print MDP to upper left of screen in white on light magenta
mov ax, 0xb800
mov es, ax
mov word [es:0x0000], 0x57<<8 | 'M'
mov word [es:0x0002], 0x57<<8 | 'D'
mov word [es:0x0004], 0x57<<8 | 'P'
; Infinite loop so we don't have the CPU wander memory
cli
endloop:
hlt
jmp endloop
我不确定此行是否是拼写错误,或者您在汇编文件上使用某种类型的预处理器,然后再将它们传递给 NASM 。通常,此行在%
:
1
符号会出现问题
dw %1 ; Number of sectors to be loaded
NASM 只会直接支持这一点:
dw 1 ; Number of sectors to be loaded
如果您尝试使用USB在真实硬件上启动,那么即使您使用上述更改在 BOCHS 中工作,您也可能会遇到其他问题。如果您的BIOS设置为进行USB FDD仿真(而不是USB HDD或其他),则可能需要在引导加载程序的开头添加Boot Parameter Block(BPB)。你可以像这样创建一个假的:
org 0x7c00
bits 16
boot:
jmp main
TIMES 3-($-$$) DB 0x90 ; Support 2 or 3 byte encoded JMPs before BPB.
; Dos 4.0 EBPB 1.44MB floppy
OEMname: db "mkfs.fat" ; mkfs.fat is what OEMname mkdosfs uses
bytesPerSector: dw 512
sectPerCluster: db 1
reservedSectors: dw 1
numFAT: db 2
numRootDirEntries: dw 224
numSectors: dw 2880
mediaType: db 0xf0
numFATsectors: dw 9
sectorsPerTrack: dw 18
numHeads: dw 2
numHiddenSectors: dd 0
numSectorsHuge: dd 0
driveNum: db 0
reserved: db 0
signature: db 0x29
volumeID: dd 0x2d7e5a1a
volumeLabel: db "NO NAME "
fileSysType: db "FAT12 "
main:
cli
xor ax, ax ; Explicitly set DS and ES to 0
mov ds, ax
mov es, ax
[rest of your code here]
如果您要修改代码以使Unix / Linux file
命令上方的布局可能能够转储它认为构成磁盘映像中MBR的BPB数据。运行命令file disk.img
,您可以获得此输出:
disk.img:DOS / MBR引导扇区,代码偏移量0x3c + 2,OEM-ID&#34; mkfs.fat&#34;,根条目224,扇区2880(卷<= 32 MB),扇区/ FAT 9,扇区/磁道18,序列号0x2d7e5a1a,未标记,FAT(12位)
以下代码将检查BIOS中是否提供Int 13h扩展,还将确定 DL 中的驱动器是否支持Int 13h扩展。如果出现故障,代码将打印相应的错误。 print_string
函数用于使用BIOS TTY输出向控制台显示字符串,并提供print_hex_word
函数以十六进制显示启动驱动器号。
org 0x7c00
bits 16
section .text
boot:
jmp main
TIMES 3-($-$$) DB 0x90 ; Support 2 or 3 byte encoded JMPs before BPB.
; Dos 4.0 EBPB 1.44MB floppy
OEMname: db "mkfs.fat" ; mkfs.fat is what OEMname mkdosfs uses
bytesPerSector: dw 512
sectPerCluster: db 1
reservedSectors: dw 1
numFAT: db 2
numRootDirEntries: dw 224
numSectors: dw 2880
mediaType: db 0xf0
numFATsectors: dw 9
sectorsPerTrack: dw 18
numHeads: dw 2
numHiddenSectors: dd 0
numSectorsHuge: dd 0
driveNum: db 0
reserved: db 0
signature: db 0x29
volumeID: dd 0x2d7e5a1a
volumeLabel: db "NO NAME "
fileSysType: db "FAT12 "
main:
cli
cld ; String instructions forward movement
xor ax, ax
mov ds, ax
mov es, ax
; Setup 4K stack before this bootloader
mov ss, ax
mov sp, 0x7c00
; Display a banner to know our bootloader is executing
mov si, msg_booting
call print_string
; Check that Int 13h Extensions are available
; http://www.ctyme.com/intr/rb-0706.htm
mov ah, 0x41 ; Int 13h/AH=41h: Check if extensions present
mov bx, 0x55aa
int 0x13
jc ext_drv_none ; CF set - no extensions available for drive
cmp bx, 0xaa55 ; Is BX 0xaa55?
jnz ext_none ; If not, int 13h extensions not supported
; by BIOS at all.
; Int 13h extensions supported by BIOS and drive at this point
; Load next sectors
mov si, DAP
mov ah, 42h
; DL didn't changed
int 13h
; Start
jmp bootend
; Error: BIOS doesn't support Int 13h extensions
ext_none:
mov si, err_no_extensions
call print_string
jmp error_end
; Error: BIOS supports Int 13h extensions but not for drive in DL
ext_drv_none:
mov si, err_no_drv_ext_support
call print_string
; Print the boot drive number in hex
xor dh, dh ; Zero extended drive number to all of DX
push word 0x00 ; Attribute and page number to write to
push dx ; The value to write as hex
call print_hex_word
error_end:
cli
.loop:
hlt
jmp .loop
; Print 16 bit value passed on stack as first parameter
; in hexadecimal. Use page number and foreground color
; passed in second parameter. This routine will work on 8086+
; processors. This code takes advantage of packed BCD to
; determine the ASCII values to print. This code could have
; used compare and branch to do the same or a translation table.
print_hex_word:
push bp
mov bp, sp ; BP=SP, on 8086 can't use sp in memory operand
push dx ; Save all registers we clobber
push cx
push bx
push ax
mov cx, 0x0404 ; CH = number of nibbles to process = 4 (4*4=16 bits)
; CL = Number of bits to rotate each iteration = 4 (a nibble)
mov dx, [bp+4] ; DX = word parameter on stack at [bp+4] to print
mov bx, [bp+6] ; BX = page / foreground attr is at [bp+6]
.loop:
rol dx, cl ; Roll 4 bits left. Lower nibble is value to print
mov ax, 0x0e0f ; AH=0E (BIOS tty print),AL=mask to get lower nibble
and al, dl ; AL=copy of lower nibble
add al, 0x90 ; Work as if we are packed BCD
daa ; Decimal adjust after add.
; If nibble in AL was between 0 and 9, then CF=0 and
; AL=0x90 to 0x99
; If nibble in AL was between A and F, then CF=1 and
; AL=0x00 to 0x05
adc al, 0x40 ; AL=0xD0 to 0xD9
; or AL=0x41 to 0x46
daa ; AL=0x30 to 0x39 (ASCII '0' to '9')
; or AL=0x41 to 0x46 (ASCII 'A' to 'F')
int 0x10 ; Print ASCII character in AL
dec ch
jnz .loop ; Go back if more nibbles to process
pop ax ; Restore registers
pop bx
pop cx
pop dx
pop bp
ret
; Print string pointed to by DS:SI using
; BIOS TTY output via int 10h/AH=0eh
print_string:
push ax
push si
mov ah, 0Eh ; int 10h 'print char' function
.repeat:
lodsb ; Get character from string
test al, al
je .done ; If char is zero, end of string
int 10h ; Otherwise, print it
jmp .repeat
.done:
pop si
pop ax
ret
; Disk address packet
DAP:
db 10h, 0
dw 1 ; Number of sectors to be loaded
dd bootend
dq 1
msg_booting: db "Booting... ", 0x00
err_no_extensions: db "Int 13h extensions not supported by BIOS", 0x00
err_no_drv_ext_support: db "Int 13h Extensions not supported on drive 0x", 0x00
; Fill the rest of bootsector with zeroes and end it
times 510 - ($ - boot) db 0
dw 0xAA55
bootend:
mov ax, 0xb800
mov es, ax
mov word [es:0x0000], 0x57<<8 | 'M'
mov word [es:0x0002], 0x57<<8 | 'D'
mov word [es:0x0004], 0x57<<8 | 'P'
cli
hlt
使用这些信息将其作为上面的硬盘图像,当我在 BOCHS 中运行时,我得到了这个输出:
如果我在 BOCHS 中启动与软盘(磁盘A :)相同的图像,则错误消息现在告诉我Int 13h扩展不可用于驱动器0x0000:
如果您发现需要阅读不支持Int 13h扩展的设备,则必须回退到reading(AH = 02)/ {{的标准Int 13h磁盘子功能3}}(AH = 03)。