jmp to protected mode The Long Walk.Chapter1.2.1

我最近忙于阅读《oranges一个操作系统的实现》，感觉作者功力还算不错，可以作为长期编写OS的参考书，目前已经读了30几页，读到了进入保护模式的一段代码，不知怎么的有些感动，因此提前更新，将这段代码放在下面：

I have been reading ‘Oranges to realize a operating system’, and I suppose the writer is quite knowledgeable. Since this could be regarded a reference book for me to write the OS. And I have read for 20 pages, the content is about protected mode. After comprehending the code about jumping to protected mode, I was moved by it unreasonably…thus I would like to put those code at here:

%include "pm.inc"
org 07c00h
jmp LABEL_BEGIN

[Section .GDT]
;GDT
;						       段基址， 段界限， 属性
LABEL_GDT:			    Descriptor	0, 0, 0							；空描述符
LABEL_DESC_CONDE32: Descriptor	0, SegCode32Len - 1, DA_C + DA_32	；非一致代码段
LABEL_DESC_VIDEO:	   Descriptor   0B8000h, 0ffffh, DA_DRW			；显存首地址
;GDT结束

GdtLen	equ	$ - LABEL											；GDT长度
Gdtptr	dw	GdtLen - 1											；GDT界限
????
；GDT选择子
SelectorCode32	equ		LABEL_DESC_CONDE32 - LABEL_GDT
SelectorVideo	equ 		LABEL_DESC_VIDEO - LABEL_GDT
；END of [SECTION .gdt]

[SECTION .s16]
[BITS 16]
LABEL_BEGIN:
mov ax, cs
mov ds, ax
mov es, as
mov ss, ax
mov sp, 0100h
;初始化32位代码段描述符
xor eax, eax
mov ax, cx
shl eax, 4
add eax, LABEL_DESC_CONDE32
shr word [LABEL_DESC_CONDE32 + 4], al
mov byte [LABEL_DESC_CONDE32 + 7], ah
;为加载GDTR做准备
xor eax, eax
mov ax, ds
shl eax, 4
add eax, LABEL_GDT											;eax <- gdt基地址
mov dword [GdtPrt + 2], eax 									;[GdtPtr + 2] <- gdt基地址
lgdt [GdtPtr]
;关中断
cli

;打开地址线A20
in al, 92h
or al, 00000010b
;准备切换到保护模式
mov eax, cr0
or eax, 1
mov cr0, eax
;真正进入保护模式
jmp				dword SelectorCode						;执行这一句会把SelectorCode32装入cs
;END of [SECTION .s16]

[SECTION .s32]
[BITS 32]
mov ax, SelectorVideo
mov gs, ax												;视频段选择子（目的）
mov edi, (80 * 11 + 79) * 2									;屏幕第11行，第79列
mov ah, 0ch												;0000:黑底 1100:红字
mov al, 'P'
mov [gs:edi], ax

;到此停止
jmp $
SegCode32Len equ 	$ - LABEL_SEG_CODE32
;END of [SECTION .s32]

And I also done some works about Assembly language in recent, but have not been compiled well, so I would not post it this time.