保护模式寻址

我正在试用引导加载程序开发教程。我能够使用FAT12约定阅读stage2引导加载程序。现在,我正在尝试以实模式加载内核,然后将其复制到0x0100000地址。

复制+跳转到0x0100000时,我出现三重错误。 基本上,我不知道如何访问或跳转到0x0100000。

当我使用

IMAGE_PMODE_BASE equ 0x1000
IMAGE_RMODE_BASE equ 0x1000

krnl32.bin: boot/kernel_entry.o ${OBJ}
    i386-elf-ld -o $@ -Ttext 0x01000 $^ --oformat binary

我错过了什么?我读到了关于描述符:保护模式下的偏移寻址,它说DESC:offset(16位)。此外,使用GDT中的粒度设置将偏移量乘以4KB。

我已经这样设置了gdt:

gdt_start: 
    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_start - 1   ; limit (Size of GDT)
    dd gdt_start            ; base of GDT

; give the descriptor offsets names

NULL_DESC equ 0
CODE_DESC equ 0x8
DATA_DESC equ 0x10

我正在链接内核,如下所示:

krnl32.bin: boot/kernel_entry.o ${OBJ}
    i386-elf-ld -o $@ -Ttext 0x0100000 $^ --oformat binary

阶段2引导加载程序

[bits 16]
[org 0x500]

jmp main

%include "boot/stage2/print16.s"
%include "boot/stage2/print32.s"
%include "boot/stage2/floppy16_driver.s"
%include "boot/stage2/fat12.s"
%include "boot/stage2/gdt.s"
%include "boot/stage2/a20.s"

;*******************************************************
;   Data Section
;*******************************************************

msgFailure db 0x0D, 0x0A, "Failed", 0x00
welcomeMessage db 0x0D, 0x0A, "Landed in STAGE TWO...", 0x00
enableA20Msg db 0x0D, 0x0A, "Enabled A20. Installed GDT", 0x00
ImageName     db "KRNL32  BIN"
ImageSize     db 0
IMAGE_PMODE_BASE equ 0xffff
IMAGE_RMODE_BASE equ 0x1000


main:
    ;-------------------------------;
    ;   Setup segments and stack    ;
    ;-------------------------------;

    cli                    ; clear interrupts
    xor     ax, ax             ; null segments
    mov     ds, ax
    mov     es, ax
    mov     ax, 0x0000         ; stack begins at 0x9000-0xffff
    mov     ss, ax
    mov     sp, 0xFFFF
    sti                    ; enable interrupts

    mov si, welcomeMessage
    call Print16

    call    _EnableA20
    call    InstallGDT
    sti
    mov si, enableA20Msg
    call Print16

    call    LoadRoot
    mov     ebx, 0
    mov     ebp, IMAGE_RMODE_BASE
    mov     esi, ImageName
    call    LoadFile        ; load our file
    mov     dword [ImageSize], ecx
    cmp     ax, 0
    je      EnterStage3
    mov     si, msgFailure
    call    Print16
    mov     ah, 0
    int     0x16                    ; await keypress
    int     0x19                    ; warm boot computer

    jmp $;

EnterStage3:

    cli   
    mov eax, cr0
    or  eax, 1
    mov cr0, eax

    jmp CODE_DESC:Stage3           


[bits 32]
Stage3:
    mov ax, DATA_DESC       ; set data segments to data selector (0x10)
    mov ds, ax
    mov ss, ax
    mov es, ax
    mov esp, 90000h     ; stack begins from 90000h

CopyImage:
    mov eax, dword [ImageSize]
    movzx   ebx, word [bpbBytesPerSector]
    mul ebx
    mov ebx, 4
    div ebx
    cld
    mov    esi, IMAGE_RMODE_BASE
    mov edi, IMAGE_PMODE_BASE
    mov ecx, eax
    rep movsd                   ; copy image to its protected mode address
    jmp IMAGE_PMODE_BASE
    jmp $;