我想制作一个玩具操作系统，但我陷入了引导加载程序阶段。
我只是想写一个非常简单的引导加载程序来加载我的主要C代码，我不太喜欢x86汇编，发生的事情是在第二阶段引导加载程序中，切换到 protected /32位模式后，我调用我的kmain() c使用 extern 关键字的函数似乎会进入某种无限重启循环，或者 qemu 崩溃并出现此错误“尝试在 RAM 或 ROM 之外的 0x000a0000 处执行代码”
我还有一些基于 x86 汇编程序的函数来将文本打印到屏幕上，如果使用这些函数，效果很好，但是调用 extern c 函数会导致上述错误
“流程”是这样的 bootloader.asm(第一阶段引导加载程序)->Stage2.asm(第二阶段引导加载程序)->kmain.cpp 在Stage2.asm中设置GDT、堆栈、A20以启动保护模式/32位模式，然后调用extern kmain函数。kmain() c++文件仅尝试将一个带有颜色的字符写入VGA缓冲区
我在 UBuntu 18.04 主机上，使用 nasm 进行汇编，使用 gcc 进行链接和 c 编译，使用 qemu 来测试这个所谓的操作系统
这些是我用来构建和运行的命令
nasm -f elf bootload.asm -o bootload.o
nasm -f elf Stage2.asm -o stage2.o
gcc -m32 stage2.o bootload.o kmain.cpp -o kernel.bin -g -nostdlib -ffreestanding -std=c++11 -mno-red-zone -fno-exceptions -nostdlib -fno-rtti -Wall -Wextra -Werror -T linker.ld
qemu-system-i386 -fda kernel.bin
这是我的bootloader.asm
[bits 16]
section .boot
global boot
boot:
hello: db "Hello world!",0
mov si,hello
mov ah,0x0e
.loop:
lodsb
or al,al
jz diskboot
int 0x10
jmp .loop
diskboot:
mov ax,0x800
mov es,ax
xor bx,bx
mov ah,0x2
mov al,0x1
mov ch,0x0
mov cl,0x2
mov dh,0x0
int 0x13
jmp 0x800:0
Stage2.asm
section .kernel
bits 16
jmp main ; go to start
;*******************************************************
; Preprocessor directives
;*******************************************************
%include "stdio.inc" ; basic i/o routines
%include "Gdt.inc" ; Gdt routines
%include "A20.inc" ; A20 enabling
;*******************************************************
; Data Section
;*******************************************************
LoadingMsg db 0x0D, 0x0A, "Searching for Operating System...", 0x00
main:
cli ; clear interrupts
xor ax, ax ; null segments
mov ds, ax
mov es, ax
mov ax, 0x9000 ; stack begins at 0x9000-0xffff
mov ss, ax
mov sp, 0xFFFF
sti ; enable interrupts
call InstallGDT ; install our GDT
call EnableA20_KKbrd_Out
mov si, LoadingMsg
call Puts16
EnterStage3:
cli ; clear interrupts
mov eax, cr0 ; set bit 0 in cr0--enter pmode
or eax, 1
mov cr0, eax
jmp CODE_DESC:Stage3 ; far jump to fix CS
bits 32
Stage3:
mov ax, DATA_DESC
mov ds, ax
mov ss, ax
mov es, ax
mov fs, ax
mov gs, ax
mov ebp, 0x90000
mov esp, ebp
extern kmain
call kmain
cli
hlt
msg db 0x0A, "<[ OS Development Series Tutorial 10 ]>", 0x0A, 0
A20.inc
;********************************************
; Enable A20 address line
;
; OS Development Series
;********************************************
%ifndef __A20_INC_67343546FDCC56AAB872_INCLUDED__
%define __A20_INC_67343546FDCC56AAB872_INCLUDED__
bits 16
;----------------------------------------------
; Enables a20 line through keyboard controller
;----------------------------------------------
EnableA20_KKbrd:
cli
push ax
mov al, 0xdd ; send enable a20 address line command to controller
out 0x64, al
pop ax
ret
;--------------------------------------------
; Enables a20 line through output port
;--------------------------------------------
EnableA20_KKbrd_Out:
cli
pusha
call wait_input
mov al,0xAD
out 0x64,al ; disable keyboard
call wait_input
mov al,0xD0
out 0x64,al ; tell controller to read output port
call wait_output
in al,0x60
push eax ; get output port data and store it
call wait_input
mov al,0xD1
out 0x64,al ; tell controller to write output port
call wait_input
pop eax
or al,2 ; set bit 1 (enable a20)
out 0x60,al ; write out data back to the output port
call wait_input
mov al,0xAE ; enable keyboard
out 0x64,al
call wait_input
popa
sti
ret
; wait for input buffer to be clear
wait_input:
in al,0x64
test al,2
jnz wait_input
ret
; wait for output buffer to be clear
wait_output:
in al,0x64
test al,1
jz wait_output
ret
;--------------------------------------
; Enables a20 line through bios
;--------------------------------------
EnableA20_Bios:
pusha
mov ax, 0x2401
int 0x15
popa
ret
;-------------------------------------------------
; Enables a20 line through system control port A
;-------------------------------------------------
EnableA20_SysControlA:
push ax
mov al, 2
out 0x92, al
pop ax
ret
%endif
Gdt.inc
;*************************************************
; Gdt.inc
; -GDT Routines
;
; OS Development Series
;*************************************************
%ifndef __GDT_INC_67343546FDCC56AAB872_INCLUDED__
%define __GDT_INC_67343546FDCC56AAB872_INCLUDED__
bits 16
;*******************************************
; InstallGDT()
; - Install our GDT
;*******************************************
InstallGDT:
cli ; clear interrupts
pusha ; save registers
lgdt [toc] ; load GDT into GDTR
sti ; enable interrupts
popa ; restore registers
ret ; All done!
;*******************************************
; Global Descriptor Table (GDT)
;*******************************************
gdt_data:
dd 0 ; null descriptor
dd 0
; gdt code: ; code descriptor
dw 0FFFFh ; limit low
dw 0 ; base low
db 0 ; base middle
db 10011010b ; access
db 11001111b ; granularity
db 0 ; base high
; gdt data: ; data descriptor
dw 0FFFFh ; limit low (Same as code)10:56 AM 7/8/2007
dw 0 ; base low
db 0 ; base middle
db 10010010b ; access
db 11001111b ; granularity
db 0 ; base high
end_of_gdt:
toc:
dw end_of_gdt - gdt_data - 1 ; limit (Size of GDT)
dd gdt_data ; base of GDT
; give the descriptor offsets names
%define NULL_DESC 0
%define CODE_DESC 0x8
%define DATA_DESC 0x10
%endif ;__GDT_INC_67343546FDCC56AAB872_INCLUDED__
linker.ld
ENTRY(boot)
OUTPUT_FORMAT("binary")
SECTIONS {
. = 0x7c00;
.boot :
{
*(.boot)
}
. = 0x7dfe;
.sig : {
SHORT(0xaa55);
}
. = 0x8000;
.kernel : AT(0x7e00) /* place immediately after the boot sector */
{
*(.kernel)
*(.text)
*(.rodata)
*(.data)
*(.bss)
*(COMMON)
}
kernel_sectors = (SIZEOF(.kernel) + 511) / 512;
/DISCARD/ : {
*(.eh_frame)
}
}
kmain.cpp
extern "C" void kmain()
{
unsigned char* vga = (unsigned char*) 0xb8000;
vga[0] = 'S';
vga[1] = 0x09;
for(;;);
}
编辑:添加stdio.inc
%ifndef __STDIO_INC_67343546FDCC56AAB872_INCLUDED__
%define __STDIO_INC_67343546FDCC56AAB872_INCLUDED__
;==========================================================
;
; 16 Bit Real Mode Routines
;==========================================================
;************************************************;
; Puts16 ()
; -Prints a null terminated string
; DS=>SI: 0 terminated string
;************************************************;
bits 16
Puts16:
pusha ; save registers
.Loop1:
lodsb ; load next byte from string from SI to AL
or al, al ; Does AL=0?
jz Puts16Done ; Yep, null terminator found-bail out
mov ah, 0eh ; Nope-Print the character
int 10h ; invoke BIOS
jmp .Loop1 ; Repeat until null terminator found
Puts16Done:
popa ; restore registers
ret ; we are done, so return
;==========================================================
;
; 32 Bit Protected Mode Routines
;==========================================================
bits 32
%define VIDMEM 0xB8000 ; video memory
%define COLS 80 ; width and height of screen
%define LINES 25
%define CHAR_ATTRIB 63 ; character attribute (White text on light blue background)
_CurX db 0 ; current x/y location
_CurY db 0
;**************************************************;
; Putch32 ()
; - Prints a character to screen
; BL => Character to print
;**************************************************;
Putch32:
pusha ; save registers
mov edi, VIDMEM ; get pointer to video memory
;-------------------------------;
; Get current position ;
;-------------------------------;
xor eax, eax ; clear eax
;--------------------------------
; Remember: currentPos = x + y * COLS! x and y are in _CurX and _CurY.
; Because there are two bytes per character, COLS=number of characters in a line.
; We have to multiply this by 2 to get number of bytes per line. This is the screen width,
; so multiply screen with * _CurY to get current line
;--------------------------------
mov ecx, COLS*2 ; Mode 7 has 2 bytes per char, so its COLS*2 bytes per line
mov al, byte [_CurY] ; get y pos
mul ecx ; multiply y*COLS
push eax ; save eax--the multiplication
;--------------------------------
; Now y * screen width is in eax. Now, just add _CurX. But, again remember that _CurX is relative
; to the current character count, not byte count. Because there are two bytes per character, we
; have to multiply _CurX by 2 first, then add it to our screen width * y.
;--------------------------------
mov al, byte [_CurX] ; multiply _CurX by 2 because it is 2 bytes per char
mov cl, 2
mul cl
pop ecx ; pop y*COLS result
add eax, ecx
;-------------------------------
; Now eax contains the offset address to draw the character at, so just add it to the base address
; of video memory (Stored in edi)
;-------------------------------
xor ecx, ecx
add edi, eax ; add it to the base address
;-------------------------------;
; Watch for new line ;
;-------------------------------;
cmp bl, 0x0A ; is it a newline character?
je .Row ; yep--go to next row
;-------------------------------;
; Print a character ;
;-------------------------------;
mov dl, bl ; Get character
mov dh, CHAR_ATTRIB ; the character attribute
mov word [edi], dx ; write to video display
;-------------------------------;
; Update next position ;
;-------------------------------;
inc byte [_CurX] ; go to next character
; cmp byte [_CurX], COLS ; are we at the end of the line?
; je .Row ; yep-go to next row
jmp .done ; nope, bail out
;-------------------------------;
; Go to next row ;
;-------------------------------;
.Row:
mov byte [_CurX], 0 ; go back to col 0
inc byte [_CurY] ; go to next row
;-------------------------------;
; Restore registers & return ;
;-------------------------------;
.done:
popa ; restore registers and return
ret
;**************************************************;
; Puts32 ()
; - Prints a null terminated string
; parm\ EBX = address of string to print
;**************************************************;
Puts32:
;-------------------------------;
; Store registers ;
;-------------------------------;
pusha ; save registers
push ebx ; copy the string address
pop edi
.loop:
;-------------------------------;
; Get character ;
;-------------------------------;
mov bl, byte [edi] ; get next character
cmp bl, 0 ; is it 0 (Null terminator)?
je .done ; yep-bail out
;-------------------------------;
; Print the character ;
;-------------------------------;
call Putch32 ; Nope-print it out
;-------------------------------;
; Go to next character ;
;-------------------------------;
inc edi ; go to next character
jmp .loop
.done:
;-------------------------------;
; Update hardware cursor ;
;-------------------------------;
; Its more efficiant to update the cursor after displaying
; the complete string because direct VGA is slow
mov bh, byte [_CurY] ; get current position
mov bl, byte [_CurX]
call MovCur ; update cursor
popa ; restore registers, and return
ret
;**************************************************;
; MoveCur ()
; - Update hardware cursor
; parm/ bh = Y pos
; parm/ bl = x pos
;**************************************************;
bits 32
MovCur:
pusha ; save registers (aren't you getting tired of this comment?)
;-------------------------------;
; Get current position ;
;-------------------------------;
; Here, _CurX and _CurY are relitave to the current position on screen, not in memory.
; That is, we don't need to worry about the byte alignment we do when displaying characters,
; so just follow the forumla: location = _CurX + _CurY * COLS
xor eax, eax
mov ecx, COLS
mov al, bh ; get y pos
mul ecx ; multiply y*COLS
add al, bl ; Now add x
mov ebx, eax
;--------------------------------------;
; Set low byte index to VGA register ;
;--------------------------------------;
mov al, 0x0f
mov dx, 0x03D4
out dx, al
mov al, bl
mov dx, 0x03D5
out dx, al ; low byte
;---------------------------------------;
; Set high byte index to VGA register ;
;---------------------------------------;
xor eax, eax
mov al, 0x0e
mov dx, 0x03D4
out dx, al
mov al, bh
mov dx, 0x03D5
out dx, al ; high byte
popa
ret
;**************************************************;
; ClrScr32 ()
; - Clears screen
;**************************************************;
bits 32
ClrScr32:
pusha
cld
mov edi, VIDMEM
mov cx, 2000
mov ah, CHAR_ATTRIB
mov al, ' '
rep stosw
mov byte [_CurX], 0
mov byte [_CurY], 0
popa
ret
;**************************************************;
; GotoXY ()
; - Set current X/Y location
; parm\ AL=X position
; parm\ AH=Y position
;**************************************************;
bits 32
GotoXY:
pusha
mov [_CurX], al ; just set the current position
mov [_CurY], ah
popa
ret
%endif ;__STDIO_INC_67343546FDCC56AAB872_INCLUDED__
最佳答案
stdio.inc 具有已在 32 位保护模式下使用 x86 汇编器写入 VGA 帧缓冲区的函数，这些函数与我也尝试写入帧缓冲区的 C 代码冲突。
删除 stdio.inc 及其函数的所有引用已经解决了该问题
我现在可以写入 VGA 缓冲区并使用 C 代码在屏幕上显示彩色文本。
关于c - 外部 C 代码无法从两阶段 x86 引导加载程序执行？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/60640575/