加载没有文件系统的内核 - osdev

Question

我构建了一个引导加载程序来将内核加载到内存中。内核代码位于软盘的扇区上。2 阶段引导加载程序从软盘中读出原始内存字节，并将其放在内存上并执行内核。这在 bochs 模拟器上效果很好，但在 qemu 模拟器上失败。

一些教程建议将内核文件保存在文件系统(如 FAT12)上，然后从中读取文件。 所以，我想问一下，这样的系统真的可以在物理机器上运行，还是会像在 qemu 模拟器上一样失败？同样，以这种方式读取内核好吗？

将来我可能会用 C 实现文件系统，而不是使用程序集在引导加载程序中执行此操作

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：第一阶段引导加载程序在Qemu和Bochs上成功加载第二阶段。 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 2 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

打印32.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

生成文件

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，则无法从文件加载内核。

我见过的大多数传统BIOS教程都没有将内核放在文件中;相反，它们只是将引导加载程序和内核连接成一个原始二进制文件，并将其重命名为软盘映像。这样，您可以直接从磁盘的扇区加载内核。