我的自定义引导加载程序中有代码从地址 0x8E00 处的 512 字节缓冲区复制内存。进入高内存，0x100000和更高。这在某些计算机上运行良好，而在其他计算机上崩溃(我假设是三重故障)。此代码在 Bochs x86 模拟器中也能正常工作。

我尝试用 rep movsb 替换自定义段偏移复制循环, 设置 esiVà edi到适当的地址，发现这在某些计算机上也会出现故障。这有什么理由失败吗？

引导加载.asm:

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; may be used to endorse or promote products derived from this software
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BOOTLOADER_SECTORS equ 3 ; includes first sector, loaded by 

BIOS

; a boot sector that enters 32-bit protected mode
        BITS 16
        ORG 0x7c00

        jmp short bootloader_start ; Jump past disk description section
        nop ; Pad out before disk description


; ------------------------------------------------------------------
; Disk description table, to make it a valid floppy
; Note: some of these values are hard-coded in the source!
; Values are those used by IBM for 1.44 MB, 3.5" diskette

OEMLabel db "OLIVEOS " ; Disk label
BytesPerSector dw 512 ; Bytes per sector
SectorsPerCluster db 1 ; Sectors per cluster
ReservedForBoot dw BOOTLOADER_SECTORS ; Reserved sectors for boot record
NumberOfFats db 2 ; Number of copies of the FAT
RootDirEntries dw 224 ; Number of entries in root dir
                                        ; (224 * 32 = 7168 = 14 sectors to read)
LogicalSectors dw 2880 ; Number of logical sectors
MediumByte db 0F0h ; Medium descriptor byte
SectorsPerFat dw 9 ; Sectors per FAT
SectorsPerTrack dw 18 ; Sectors per track (36/cylinder)
Sides dw 2 ; Number of sides/heads
HiddenSectors dd 0 ; Number of hidden sectors
LargeSectors dd 0 ; Number of LBA sectors
DriveNo dw 0 ; Drive No: 0
Signature db 41 ; Drive signature: 41 for floppy
VolumeID dd 00000000h ; Volume ID: any number
VolumeLabel db "OLIVEOS "; Volume Label: any 11 chars
FileSystem db "FAT12 " ; File system type: don't change!

        KERNEL_OFFSET equ 0x100000 ; kernel load offset
        STACK_LOCATION equ 0x7c00 ; stack location
        MEM_MAP_ENTRIES equ 0x5000 ; memory map length offset
        MEM_MAP_OFFSET equ 0x5004 ; memory map offset

bootloader_start:
        ; NOTE: A few early BIOSes are reported to improperly set DL

        cmp dl, 0
        je no_change
        mov [BOOT_DRIVE], dl ; Save boot device number
        mov ah, 8 ; Get drive parameters
        int 13h
        jc disk_error
        and cx, 3Fh ; Maximum sector number
        mov [SectorsPerTrack], cx ; Sector numbers start at 1
        movzx dx, dh ; Maximum head number
        add dx, 1 ; Head numbers start at 0 - add 1 for total
        mov [Sides], dx

no_change:
        mov eax, 0 ; Needed for some older BIOSes

        cli
        xor ax, ax ; make AX zero
        mov ds, ax ; so we point our segment registers to zero
        mov es, ax
        mov fs, ax
        mov gs, ax
        mov ss, ax

        jmp 0x0000:bootloader_landing ; far jump to clear cs to 0

bootloader_landing:
        mov bp, STACK_LOCATION ; set up stack
        mov sp, bp

        sti

        mov si, MSG_STARTING_BOOTLOADER
        call bios_print_string

        call load_bootloader ; load the rest of the bootloader (if we don't do it first,
                                        ; something is very likely going to mess up)

        pusha
        mov di, MEM_MAP_OFFSET
        jmp bios_get_memory ; get memory map for kernel
bios_get_memory_return:
        popa

        mov bp, STACK_LOCATION ; set up stack again (bios_get_memory trashed our stack)
        mov sp, bp

        jmp second_stage ; transfer control to second stage!

; loads the rest of this bootloader
load_bootloader:
        mov bx, second_stage ; read to 0x7e00 (right after this 512 byte code segment)
        mov al, BOOTLOADER_SECTORS-1 ; sectors to read
        mov dl, [BOOT_DRIVE] ; drive
        mov cl, 0x02 ; start sector
        mov ch, 0x00 ; cylinder
        mov dh, 0x00 ; head
        mov ah, 0x02 ; BIOS read sector function

        push ax ; store AX on stack so later we can recall
                                        ; how many sectors were request to be read,
                                        ; even if it is altered in the meantime

        int 0x13 ; call BIOS

        jc disk_error ; jump if error (carry flag set)

        pop dx ; restore from stack (was AX before)
        cmp dl, al ; if AL (sectors read) != DH (sectors expected)
        jne disk_error ; display error message

        trở về

; displays error message and hangs
disk_error:
        mov si, DISK_ERROR_MSG
        call bios_print_string

        sti
.halt:
        hlt
        jmp .halt

; -----------------------------------------------------------------
; BOOTLOADER SUBROUTINES:
;
bios_print_string:
        pusha

        mov ah, 0x0e ; int 10h teletype function

.repeat:
        lodsb ; Get char from string

        cmp al, 0
        je .done ; If char is zero, end of string

        int 0x10 ; Otherwise, print it
        jmp .repeat ; And move on to next char

.done:
        popa
        trở về

; prints 16 bit hex value from AX
bios_print_2hex:
        push cx

        mov cx, 16-4
.repeat:        
        push ax

        shr ax, cl
        and ax, 0xf
        cmp ax, 9
        jle .print

        add ax, 'A'-'9'-1

.print:
        add ax, '0'
        mov ah, 0x0e
        int 0x10

        pop ax

        cmp cx, 0
        je .done

        sub cx, 4
        jmp .repeat;
.done:
        pop cx
        trở về

; prints 32 bit hex value from AX
bios_print_4hex:
        push eax

        shr eax, 16
        call bios_print_2hex

        pop eax
        and eax, 0xffff
        call bios_print_2hex

        trở về

; global variables
BOOT_DRIVE db 0
MSG_STARTING_BOOTLOADER db "OliveOS", 0
MSG_STARTING_SECOND_STAGE db " has started!", 0
MSG_READING db ".", 0
MSG_READING2 db "!", 0
DISK_ERROR_MSG db "Disk read error!", 0
MSG_REG_DUMP db 0xD, 0xA, "INTERNAL REG DUMP", 0xD, 0xA, 0
NEWLINE db 0xD, 0xA, 0

; bootsector padding
times 510-($-$$) db 0
dw 0xaa55

        BITS 16

second_stage:
        mov si, MSG_STARTING_SECOND_STAGE
        call bios_print_string

        ;call bios_enable_a20
        call load_kernel

        jmp switch_to_pm ; switch to protected mode, we won't return from here

        BITS 32
; this is where we arrive after switching to and initializing protected mode
begin_pm:
        call kbd_enable_a20
        call fast_enable_a20

        call CODE_SEG:KERNEL_OFFSET ; now call the kernel!

.halt:
        hlt ; hang
        jmp .halt

        BITS 16

load_dest:
        dd KERNEL_OFFSET

; loads the kernel from the floppy image
load_kernel:        
        mov ax, BOOTLOADER_SECTORS ; start logical sector
        mov cx, 200 ; number of sectors to read

.continue:
        cmp cx, 0
        je .done

        pusha
        mov ebx, 0x8E00 ; write to 0x8E00 a temporary 512 byte buffer
        call bios_disk_load ; load bytes to buffer

        mov si, MSG_READING
        call bios_print_string
        popa

        pusha ; copy bytes in buffer to destination
        call switch_to_unreal ; switch to unreal mode to access high memory

        mov cx, 0x200 ; copy 512 bytes
        mov ebx, 0x8E00 ; read from 0x8E00
        mov edx, dword [load_dest] ; load destination address

.copy:
        cmp cx, 0
        je .done_copying

        mov eax, dword [fs:ebx]
        mov dword [fs:edx], eax ; commenting out this line (the actual write) will work on any computer

        add ebx, 4
        add edx, 4

        sub cx, 4
        jmp short .copy

.done_copying:
        call switch_to_real ; switch back to real mode
        popa

        add dword [load_dest], 0x200 ; add 512 bytes to output pointer
        inc ax ; increment logical sector
        dec cx ; decrement loop counter

        jmp .continue ; continue reading
.done:    
        trở về

;sets up LBA address in AX for INT 13H
logical_int13_setup:
        push bx
        push ax

        mov bx, ax ; Save logical sector

        mov dx, 0 ; First the sector
        div word [SectorsPerTrack]
        add dl, 0x01 ; Physical sectors start at 1
        mov cl, dl ; Sectors belong in CL for int 13h
        mov ax, bx

        mov dx, 0 ; Now calculate the head
        div word [SectorsPerTrack]
        mov dx, 0
        div word [Sides]
        mov dh, dl ; Head/side
        mov ch, al ; Track

        pop ax
        pop bx

        mov dl, byte [BOOT_DRIVE] ; Set correct device

        trở về

;bios_disk_load: loads logical sector in AX to ES:BX
bios_disk_load:
        call logical_int13_setup ; setup our parameters

        mov ah, 0x2 ; INT 0x13 function
        mov al, 0x1 ; load 1 sector

        int 0x13

        jc disk_error ; jump if error (carry flag set)

        cmp al, 1 ; if AL (sectors read) != 1 (sectors expected)
        jne disk_error ; display error message

        trở về

bios_reg_dump:
        pusha

        mov si, MSG_REG_DUMP
        call bios_print_string

        mov si, .MSG_AX
        call bios_print_string
        call bios_print_4hex
        mov si, NEWLINE
        call bios_print_string

        mov si, .MSG_BX
        call bios_print_string
        mov eax, ebx
        call bios_print_4hex
        mov si, NEWLINE
        call bios_print_string

        mov si, .MSG_CX
        call bios_print_string
        mov eax, ecx
        call bios_print_4hex
        mov si, NEWLINE
        call bios_print_string

        mov si, .MSG_DX
        call bios_print_string
        mov eax, edx
        call bios_print_4hex
        mov si, NEWLINE
        call bios_print_string

        mov si, .MSG_CS
        call bios_print_string
        mov eax, cs
        call bios_print_4hex
        mov si, NEWLINE
        call bios_print_string

        mov si, .MSG_DS
        call bios_print_string
        mov eax, ds
        call bios_print_4hex
        mov si, NEWLINE
        call bios_print_string

        mov si, .MSG_ES
        call bios_print_string
        mov eax, es
        call bios_print_4hex
        mov si, NEWLINE
        call bios_print_string

        mov si, .MSG_FS
        call bios_print_string
        mov eax, fs
        call bios_print_4hex
        mov si, NEWLINE
        call bios_print_string

        mov si, .MSG_GS
        call bios_print_string
        mov eax, gs
        call bios_print_4hex
        mov si, NEWLINE
        call bios_print_string

        popa
        trở về

        .MSG_AX db "EAX: 0x", 0
        .MSG_BX db "EBX: 0x", 0
        .MSG_CX db "ECX: 0x", 0
        .MSG_DX db "EDX: 0x", 0
        .MSG_CS db "CS: 0x", 0
        .MSG_DS db "DS: 0x", 0
        .MSG_ES db "ES: 0x", 0
        .MSG_FS db "FS: 0x", 0
        .MSG_GS db "GS: 0x", 0

%include "source/bootload/gdt.asm"
%include "source/bootload/protected_mode.asm"
%include "source/bootload/memory.asm"

times (BOOTLOADER_SECTORS*512)-($-$$) db 0

1 Câu trả lời

我找到了我的问题的答案。写信mov dword [fs:edx], eax失败，不是因为 fshoặc edx包含无效的段和地址，但因为在写入地址之前未启用 A20 线 0x100000和更高。相反，它后来被启用。

一些 BIOS，如 Bochs，已经设置了 A20 线，允许代码运行。其他人没有设置 A20 行，因此写入地址模 0x100000 , 地址 0x000000和更高。这是 IVT(中断向量表)存储在内存中的地方，如果被覆盖，则可以轻松地从未处理的中断和崩溃或挂起计算机中创建三重故障。解决方案？在写入高地址之前设置 A20 线。

关于assembly - 引导加载程序代码有时会崩溃(三重故障？)计算机，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/32674066/