加载没有文件系统的内核- osdev

Question

我构建了一个引导加载器来将内核加载到内存中。内核代码位于软盘的扇区上。二级引导加载程序从软盘中读取内存的原始字节，并将其放在内存中并执行内核。这在bochs模拟器上很好，但在qemu模拟器上却失败了。

一些教程建议将内核文件保存在文件系统(如FAT12)上，然后从它读取文件。所以，我想问一下，这样的系统在物理机器上真的能工作吗，还是会像qemu仿真器那样失败？用这种方式阅读内核也有好处吗？

将来我可能会用C实现一个文件系统，而不是使用程序集在引导加载程序中实现它。

qemu的问题可能是因为我的图像文件不是512字节的倍数，使得最后一个扇区不可读。

编辑：第一阶段引导加载器成功地在Qemu和Bochs上加载第二阶段。第1阶段引导加载程序是-

[org 0x7c00]

STAGE2 equ 0x800

STAGE2_SECTORS equ 2+1
TRACKS equ 2

mov [BOOT_DRIVE],dl

mov bp,0x9000
mov sp,bp

mov bx, msgReal
call print_string

call load_stage2

call STAGE2

jmp $

%include 'boot/bios.ASM'

[bits 16]
load_stage2:
    mov bx, msgStage2
    call print_string
    mov cl, 2
    mov bx, STAGE2
    mov dh, 1
    mov dl, [BOOT_DRIVE]
load_sector:
    call disk_load
    cmp cl, STAGE2_SECTORS
    je loaded
    cmp cl, 15
    add cl, 1
    add bx, 512
    jmp load_sector
loaded:
    ret

BOOT_DRIVE db 0
msgReal db "Booted in 16-bit mode",0
msgStage2 db "Loading the stage2 boot loader onto memory",0

times 510-($-$$) db 0
dw 0xaa55

第二阶段引导加载程序是-

[org 0x800]

KERNEL equ 0x1000
KERNEL_SECTORS equ 24

mov bx, msgStage2
call print_string

call load_kernel

mov bx, msg
call print_string

int 0x12
mov [0x600], ax

call switch_to_pm

%include 'boot/bios.ASM'

%include 'boot/gdt.ASM'
%include 'boot/protected_mode.ASM'
%include 'boot/print32.ASM'

[bits 16]

load_kernel:
    mov bx, msgKernel
    call print_string
    mov ax, 3
    mov cl, 4
    mov ch, 0
    mov bx, KERNEL
    mov dl, [BOOT_DRIVE]
    mov dh, 0
    mov ch, 0
load_sector:
    mov ah, 0x02
    mov al, 1
    int 0x13
    jc error1
    cmp al, 1
    jne error2
    push bx
    mov bl, [Sector]
    cmp bl, KERNEL_SECTORS
    pop bx
    je loaded
    push bx
    mov bl, [Sector]
    inc bl
    mov [Sector], bl
    pop bx
    inc cl
    cmp cl, 18
    jne continue
    add ch, 1
    mov cl, 1
continue:
    add bx, BytesPerSector
    jmp load_sector
loaded:
    ret

error1:
    mov bx, errorMsg1
    call print_string
    jmp $

error2:
    mov bx, errorMsg2
    call print_string
    jmp $

[bits 32]

BEGIN_PM:
    mov ebx, msgProt
    call print_string32
    call KERNEL
    jmp $

BytesPerSector equ 512
NumHeads equ 2
SectorsPerTrack equ 18

Sector db 0

BOOT_DRIVE db 0
msgStage2 db "Stage 2 reached!", 0
msgProt db "Successfully switched to 32-bit mode",0
msgKernel db "Loading the kernel onto memory",0
msg db "Loaded!!", 0
errorMsg1 db "Error1", 0
errorMsg2 db "Error2", 0

times 1024-($-$$) db 0

bios.asm

[bits 16]

print_string:
    pusha
    mov cx,bx
    mov ah,0x0e
    printStringStart:
    mov al,[bx]
    cmp al,0
    je done
    int 0x10
    inc bx
    jmp printStringStart
    done:
    popa
    ret

disk_load:
    pusha
    push dx
    mov ah,0x02
    mov al,dh
    mov dh,0x0
    int 0x13
    jc disk_error
    pop dx
    cmp dh,al
    jne disk_error
    popa
    ret

disk_error:
    mov ah,0x0e
    mov al,'X'
    int 0x10
    mov bx,errMsg
    call print_string
    jmp $

errMsg:
    db "Disk Read Error....."
    times 80-20 db " "
    db 0

protected_mode.asm:

[bits 16]
switch_to_pm:
    cli
    lgdt [gdt_descriptor]
    mov eax, cr0
    or eax, 0x1
    mov cr0, eax
    jmp CODE_SEG:init_pm

[bits 32]
init_pm:
    mov ax, DATA_SEG
    mov ds, ax
    mov ss, ax
    mov es, ax
    mov fs, ax
    mov gs, ax

    mov ebp,0x90000
    mov esp,0x90000

    call BEGIN_PM

print32.asm:

[bits 32]

VIDEO_MEM equ 0xb8000
DEF_COLOR equ 0x0f

print_string32:
    pusha
    mov edx,VIDEO_MEM

print_string32_loop:
    mov al, [ebx]
    mov ah, DEF_COLOR

    cmp al,0
    je print_string32_end

    mov [edx],ax

    inc ebx
    add edx,2
    jmp print_string32_loop

print_string32_end:
    popa
    ret

gdt.asm:

gdt_start:
gdt_null:
    dd 0x0
    dd 0x0

gdt_code:
    dw 0xffff
    dw 0x0
    db 0x0
    db 10011010b
    db 11001111b
    db 0x0

gdt_data:
    dw 0xffff
    dw 0x0
    db 0x0
    db 10010010b
    db 11001111b
    db 0x0
gdt_end:

gdt_descriptor:
    dw gdt_end - gdt_start - 1
    dd gdt_start

CODE_SEG equ gdt_code - gdt_start
DATA_SEG equ gdt_data - gdt_start

MakeFile

DIRECTORIES = boot kernel drivers HALx86 dataman

C_SOURCES = $(wildcard drivers/*.c HALx86/*.c dataman/*.c)
ASM_SOURCES = $(wildcard HALx86/*.asm)

CC = gcc
CFLAGS = -DDEBUG -m32 -ffreestanding -c -nostdlib

KERNEL = kernel/kernel_start.o kernel/kernel.o

ASM = nasm
AOFLAGS = -f elf32 -o
ABINFLAGS = -f bin -o

OBJ = ${C_SOURCES:.c=.o}
ASMOBJ = ${ASM_SOURCES:.asm=.o}

all: os-image.img

os-image.img: boot/boot_sector.bin boot/boot_stage2.bin kernel/kernel.bin
    cat $^ > $@
    echo "OS Image size:"
    wc -c os-image.img

kernel/kernel.bin: $(KERNEL) ${OBJ} ${ASMOBJ}
    ld -melf_i386 -o $@ -Ttext 0x1000 $^ --oformat binary

%.o : %.c
    $(CC) $(CFLAGS) $< -o $@

%.o : %.asm
    $(ASM) $< $(AOFLAGS) $@

%.bin : %.asm 
    nasm $< $(ABINFLAGS) $@

clean:
    rm -fr kernel/*.o
    rm -fr drivers/*.o
    rm -fr HALx86/*.o
    rm -fr dataman/*.o
    rm -fr boot/*.bin
    rm -fr os-image.img *.bin *.o

rebuild:
    make clean
    make

backup:
    make clean
    zip -r backups/BACKUP_DATE-`date +%d-%m-%Y_%H-%M-%S`.zip $(DIRECTORIES) README.txt makefile
    make

Answer 1

如果没有文件系统，就无法从文件中加载内核。

我见过的大多数遗留BIOS教程都没有将内核放入文件中，而是将引导加载程序和内核连接到一个原始二进制文件中，并将其重命名为软盘映像。这样，您就可以直接从磁盘的扇区加载内核。