如何解决设置GDT时Qemu无限重启
我主要使用 C++ 制作操作系统,但对于引导加载程序,我使用的是 FASM。当我尝试设置 GDT 时,Qemu 会清除屏幕并在顶部重新打印“SeaBIOS”。它会一直循环下去,直到我关闭它。这是它的gif:
我尝试使用 -nographic 运行它,但它在 Windows 控制台中执行相同的操作。
哦,是的,操作系统/版本信息。
窗户:20H2
FASM:1.73.25
Qemu:5.1.0
这是我的代码:
gdt_start:
dd 0x00
dd 0x00
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
switch_to_pm:
cli
lgdt [gdt_descriptor]
mov eax,cr0
or eax,0x1
mov cr0,eax
jmp CODE_SEG:init_pm
use32
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,ebp
call BEGIN_PM
BEGIN_PM:
mov ebx,MSG_PROT_MODE
call print_string_pm
call KERNEL_OFFSET
jmp $
更新:完整代码:
; boot.asm
org 0x7c00
KERNEL_OFFSET equ 0x1000
mov [BOOT_DRIVE],dl
mov bp,0x9000
mov sp,bp
mov bx,MSG_REAL_MODE
call print
call print_nl
call load_kernel
call switch_to_pm
jmp $
print:
pusha
start:
mov al,[bx]
cmp al,0
je done
mov ah,0x0e
int 0x10
add bx,1
jmp start
done:
popa
ret
print_nl:
pusha
mov ah,0x0e
mov al,0x0a
int 0x10
mov al,0x0d
int 0x10
popa
ret
load_kernel:
mov bx,MSG_LOAD_KERNEL
call print
call print_nl
mov bx,KERNEL_OFFSET
mov dh,1
mov dl,[BOOT_DRIVE]
call disk_load
ret
disk_load:
pusha
push dx
mov ah,0x02
mov al,dh
mov cl,0x02
mov ch,0x00
mov dh,0x00
int 0x13
jc disk_error
pop dx
cmp al,dh
jne sectors_error
popa
ret
disk_error:
mov bx,disK_ERROR
call print
call print_nl
mov dh,ah
call print_hex
jmp disk_loop
sectors_error:
mov bx,SECTORS_ERROR
call print
disk_loop:
jmp $
print_hex:
pusha
mov cx,0
hex_loop:
cmp cx,4
je end_hex
mov ax,dx
and ax,0x000f
add al,0x30
cmp al,0x39
jle step2
add al,7
step2:
mov bx,HEX_OUT + 5
sub bx,cx
mov [bx],al
ror dx,4
add cx,1
jmp hex_loop
end_hex:
mov bx,HEX_OUT
call print
popa
ret
HEX_OUT:
db '0x0000',0
gdt_start:
dd 0x00
dd 0x00
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
switch_to_pm:
cli
lgdt [gdt_descriptor]
mov eax,MSG_PROT_MODE
call print_string_pm
call KERNEL_OFFSET
jmp $
VIDEO_MEMORY equ 0xb8000
WHITE_ON_BLACK equ 0x0f
print_string_pm:
pusha
mov edx,VIDEO_MEMORY
print_string_pm_loop:
mov al,[ebx]
mov ah,WHITE_ON_BLACK
cmp al,0
je print_string_pm_done
mov [edx],ax
add ebx,1
add edx,2
jmp print_string_pm_loop
print_string_pm_done:
popa
ret
BOOT_DRIVE db 0
MSG_REAL_MODE db "Started in 16-bit real mode",0
MSG_LOAD_KERNEL db "Loading kernel into memory",0
disK_ERROR db "disk read error",0
SECTORS_ERROR db "Incorrect number of sectors read",0
MSG_PROT_MODE db "Loaded 32-bit protected mode",0
times 510-($-$$) db 0
dw 0xAA55
; loader.asm
format ELF
extrn main
public _start
_start:
call main
jmp $
// kernel.cpp
void main() {
char* video_memory = (char*) 0xb8000;
*video_memory = 'X';
}
rem compile.bat
@echo off
<NUL set /p="Cleaning binaries..."
del *.bin > NUL
del *.o > NUL
del *.elf > NUL
echo Done
<NUL set /p="Compiling boot.asm..."
fasm boot.asm > NUL
echo Done
<NUL set /p="Compiling loader.asm..."
fasm loader.asm > NUL
echo Done
<NUL set /p="Compiling kernel.c..."
wsl gcc -m32 -ffreestanding -c kernel.cpp -o kernel.o
echo Done
<NUL set /p="Linking..."
wsl objcopy kernel.o -O elf32-i386 kernel.elf
wsl /usr/local/i386elfgcc/bin/i386-elf-ld -o kernel.bin -Ttext 0x1000 loader.o kernel.elf
type boot.bin kernel.bin > os_image.bin
echo Done
<NUL set /p="Running..."
qemu-system-i386 os_image.bin
echo Done
解决方法
问题不在于代码,而在于您如何构建它。这个序列实际上创建了一个名为 kernel.bin
的 ELF 可执行文件:
wsl objcopy kernel.o -O elf32-i386 kernel.elf
wsl /usr/local/i386elfgcc/bin/i386-elf-ld -o kernel.bin -Ttext 0x1000 loader.o kernel.elf
应该是:
wsl /usr/local/i386elfgcc/bin/i386-elf-ld -o kernel.elf -Ttext 0x1000 loader.o kernel.o
wsl objcopy -O binary kernel.elf kernel.bin
此更改将目标文件链接到 ELF 可执行文件 kernel.elf
,然后将 ELF 可执行文件转换为可由引导加载程序加载到地址 0x01000 的二进制文件 kernel.bin
。
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