A toy protect-mode bootloader can display string in real/protect mode of x86.

related_info/lab1/pmbootloader/Makefile

@@ -0,0 +1,12 @@
+all:pmboot
+pmboot.s: pmboot.S
+	gcc  -E  pmboot.S > pmboot.s
+pmboot.o: pmboot.s
+	as -o pmboot.o pmboot.s
+pmboot: pmboot.o	
+	ld --oformat binary -N -e start -Ttext 0x7c00 -o pmboot pmboot.o
+run: pmboot
+	qemu-system-i386 -fda pmboot
+.PHONY: clean
+clean:
+	rm pmboot.o pmboot pmboot.s

related_info/lab1/pmbootloader/pmboot.S

@@ -0,0 +1,81 @@
+#define Descriptor(base,lim,type)\
+.word lim&0xffff;\
+.word base&0xffff;\
+.byte (base>>16)&0xff;\
+.word ((lim>>8)&0xf00)|(type&0x0f0ff);\
+.byte ((base>>24)&0xff)
+
+DA_C = 0x98
+DA_32 = 0x4000
+DA_DRW = 0x92
+
+.text
+.globl start
+.code16
+start:
+ jmpl $0x0, $code 
+		
+GDT_START:	
+Descriptor_DUMMY:Descriptor(0x0,0x0,0x0)
+Descript_CODE32 :Descriptor(0x0,0xffffffff,DA_C+DA_32)
+Descriptor_VIDEO:Descriptor(0xb8000,0x0ffff,DA_DRW)
+GDT_END:
+
+GdtPtr:
+	.word (GDT_END-GDT_START)-1	# so does gdt 
+	.long GDT_START 	# This will be rewrite by code.
+msg:
+ .string "Hello world!"
+code:
+	mov     %cs,%ax   
+	mov     %ax,%ds 
+	mov     %ax,%es    
+	mov     %ax,%ss  
+	mov  $0x8000,%sp  
+	/*显示HelloWorld字符串*/
+	mov $msg   ,%ax
+	mov %ax    ,%bp
+	mov $12    ,%cx
+	mov $0x1301,%ax
+	mov $0x000c,%bx
+	mov $0     ,%dl
+	
+	int $0x10
+	
+/*加载gdtr即将全局描述符表gdt的首地址和gdt的界限赋给gdtr寄存器*/       
+	lgdt GdtPtr
+
+/*关中断*/
+	cli
+
+/*打开地址线A20*/
+	inb $0x92,%al
+	or  $0x02,%al
+	outb %al,$0x92
+
+/*设置cr0寄存器,切换到保护模式*/
+	movl %cr0,%eax
+	or   $1,%eax
+	movl %eax,%cr0
+
+
+/*真正进入保护模式,执行此命令后CS=0x8,IP=LABEL_SEG_CODE32的偏移地址*/
+	ljmp $0x8,$(LABEL_SEG_CODE32)
+/*此时CS:IP=全局描述符表中第1(0x8>>3)项描述符给出的段基址+LABEL_SEG_CODE32的偏移地址*/
+
+
+LABEL_SEG_CODE32:
+.align  32
+.code32
+	movw $0x10,%ax
+	movw %ax,%gs
+	movl $((80*11+79)*2),%edi/*第11行，79列*/
+	movb $0x0c,%ah/*高四位表示黑底,低四位表示红字*/
+	movb $'P',%al/*显示的字符*/
+	movw %ax,%gs:(%edi)
+	
+loop2:
+	jmp loop2
+
+.org 0x1fe, 0x90 
+.word 0xaa55 

related_info/lab1/pmbootloader/pmboot.md

@@ -0,0 +1,8 @@
+From http://blog.csdn.net/guocaigao/article/details/8477929
+
+A toy protect-mode bootloader can display string in real/protect mode of x86.
+
+Try
+```
+make run
+```