未从两阶段x86引导程序执行外部C代码吗？

问题描述 投票：3回答：1

我想制作一个玩具，但是我被困在引导程序阶段。我只是想写一个非常简单的引导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程序中一次，切换到保护/ 32位模式后，我称我的[C0 ] c函数使用kmain()关键字似乎进入了某种无限的rebooot循环，或者qemu崩溃，并显示以下错误“试图在0x000a0000的RAM或ROM外部执行代码”

[我也有一些基于x86汇编器的功能，可将文本打印到屏幕上，如果使用这些功能，效果很好，但是调用extern c函数会导致上述错误

“流”是这样的bootloader.asm（第一阶段引导程序）-> Stage2.asm（第二阶段引导程序）-> 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 ++文件仅尝试将一种颜色的字符写入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，并使用qemu来测试此所谓的OS

这些是我用来构建和运行的命令

extern
这是我的bootloader.asm
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

Stage2.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 

A20.inc

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

Gdt.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

linker.ld


;*************************************************
;   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__


kmain.cpp
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)
  }
}

编辑：已添加stdio.inc
extern "C" void kmain()
{

unsigned char* vga = (unsigned char*) 0xb8000;
   vga[0] = 'S'; 
   vga[1] = 0x09; 
   for(;;); 
}

我想制作一个玩具，但是我被困在引导程序阶段。我只是想写一个非常简单的引导程序来加载我的主要C代码，我不太喜欢x86汇编，发生的事情是一次...

c assembly x86 linker bootloader
1个回答
0
投票

%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__ 的功能已经在32位保护模式下使用x86汇编器写入VGA帧缓冲区，这些功能与我的C代码（试图写入帧缓冲区）冲突。删除stdio.inc及其功能的所有引用已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。

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