X86 int 13h 42h不'；不要把任何东西装在箱子里

我将引导加载程序从CHS更改为LBA，因此我将

int13h02h

替换为

int13h42h

。它在QEMU中正常工作，但是，我用Bochs和我的笔记本电脑运行它时遇到问题

我使用

ddif=main.bin of=/dev/sdb bs=512

将引导加载程序写入USB闪存驱动器。笔记本电脑加载Intel UNDI并显示以下错误：

无可引导设备-插入引导盘并按任意键

所以我试着用Bochs调试它，注意到Bochs将这个二进制文件识别为可引导文件。但是，在执行

int13h

后，没有加载任何内容

然后我试着从这个闪存驱动器加载我的旧电脑，它工作了！它加载程序并正确执行。QEMU给了我同样的结果

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:

中银高铁：

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"

LBA磁盘访问可用性 并非所有BIOS都支持扩展磁盘读写功能（尽管在现代硬件上，它们几乎都支持）。并非所有BIOS都支持通过扩展磁盘读取软盘。博克斯也是如此。您可以通过测试驱动器上是否有扩展磁盘功能。这将执行扩展磁盘安装检查

如果您想使用扩展磁盘读取和LBA在BOCHS上测试代码，您必须创建硬盘映像并修改BOCHS以从它而不是从软盘引导。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，每个扇区512字节

您可以将您的

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"

我使用一个名为

disk.img

的磁盘映像。您可以创建它，并使用以下命令将生成的扇区放入其中：

nasm -f bin main.asm -o main.bin

创建一个516096字节的映像：

dd if=/dev/zero of=disk.img count=1008 bs=512

将引导扇区放入

disk.img

的开头，但不截断文件：

dd if=main.bin of=disk.img conv=notrunc

我有更多关于使用DD创建磁盘映像的信息

---

一般守则意见 虽然磁盘映像是BOCHS问题的一部分，但您确实存在一些编码问题。当控制权从BIOS转移到引导加载程序时，您不能假设CS的值将被设置为您认为的值。有关更多信息，请参阅我的。如果希望DS和ES为零（这是使用

org 0x7c00

所需的），则应将代码的开头修改为：

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

之后添加了以下内容：

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

NASM仅直接支持这一点：

dw 1  ; Number of sectors to be loaded

---

真正的硬件/USB/笔记本电脑问题 如果您试图使用USB在真正的硬件上引导，那么您可能会遇到另一个问题，即使您在BOCHS中通过上述更改使其正常工作。如果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一个。您可以创建一个如下所示的假文件：

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]

如果要修改代码使其布局高于Unix/Linux

文件

命令，则该命令可能能够在磁盘映像中转储它认为构成MBR的BPB数据。运行命令

file disk.img

，您可能会得到以下输出：

---

disk.img:DOS/MBR引导扇区，代码偏移量0x3c+2，OEM-ID“mkfs.fat”，根条目224，扇区2880（感谢您提供完整的答案！但是，我没有成功地遵循它。当我将BPB添加到引导扇区的开头时，QEMU没有将此二进制文件识别为可引导。我创建了硬盘映像，但Bochs为ata0从属文件写入了

未知类型“none”

。也许我应该为ata0尝试另一种类型？P.S.Sor由于注释不完整，我在编写itBuild时意外按下了Enter键：

nasm-f bin-I./lib/“main.asm-o main.bin

dd if=/dev/zero of=main.img count=1008 bs=512

dd if=main.bin of=main.img conv=notrunc

Run:

qemu-system-i386-s-m 32-drive format=raw，file=main.bin

（也尝试了

file=main.img

）当我删除BPB时，QEMU运行正常。另外，我刚刚从bochsrc中删除了ata0从机，现在Bochs运行，但似乎

int 13h 42h

即使在硬盘驱动器上也不工作，所以我将检查Bochs是否支持扩展磁盘读取。让我们来看看。

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]

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