加入system

system部分就是将来我们的内核部分，现在只有一个简单的head.S，而且就是打印一个字符‘S’，代码如下：

SETUPLEN = 4
BOOTSEG = 0x7c0
INITSEG = 0x9000
SETUPSEG = 0x9020
SYSSEG = 0x1000
ENDSEG = SYSSEG + SYSSIZE
.text  
.globl start/*程序从start处开始运行*/  
.code16  
start:
LABEL_SEG_CODE32:  
.align  32  
.code32  

    movw $0x10,%ax  
    movw %ax,%gs  
    movl $((80*12+79)*2),%edi/*第12行，79列*/  
    movb $0x0c,%ah/*高四位表示黑底,低四位表示红字*/  
    movb $'S',%al/*显示的字符*/  
    movw %ax,%gs:(%edi)                
loop1:/*无限循环*/  
    jmp loop1

我们将system部分放到setup后面，也就是第六个及以后的扇区。

Makefile如下：

AS    =as
LD    =ld
LDFLAGS   = --oformat binary -N -e start -Ttext 0x0

Image:bootsect setup head
	cat bootsect setup head >Image
	
bootsect:bootsect.s
	$(AS) -o bootsect.o -a bootsect.s
	$(LD) $(LDFLAGS) -o bootsect bootsect.o
setup:setup.s
	$(AS) -o setup.o -a setup.s
	$(LD) $(LDFLAGS) -o setup setup.o
head:head.s
	$(AS) -o head.o -a head.s
	$(LD) $(LDFLAGS) -o head head.o


clean:
	rm -f  Image setup bootsect *.o 

load_system代码将system读出放到内存0x10000处

启动扇区代码修改如下：

SETUPLEN = 4
BOOTSEG = 0x7c0
INITSEG = 0x9000
SETUPSEG = 0x9020
SYSSEG = 0x1000
ENDSEG = SYSSEG + SYSSIZE
.text  
.globl start/*程序从start处开始运行*/  
.code16  
start:  

	mov $BOOTSEG,%ax  //将ds段寄存器设置为0x07c0
	mov %ax,%ds
	mov $INITSEG,%ax	//将es段寄存器设置为0x9000
	mov %ax,%es
	mov $256,%cx
	sub %si,%si
	sub %di,%di
	rep
	movsw
	jmpl $INITSEG,$code

  
msg:  
 .string "Hello world!"  
code:  
    mov     %cs,%ax     
    mov     %ax,%ds   
    mov     %ax,%es      
    mov     %ax,%ss    
    mov  $0xff00,%sp    
    call DispStr/*调用显示字符串函数*/  
load_setup:
		movb $0x00,%dh//磁头号0
		movb $0x00,%dl//驱动器号0
		mov $0x0002,%cx
		mov $0x0200,%bx//es:bx指向缓冲区
		movb $0x02,%ah//0x02,读磁盘扇区到内存
		movb $SETUPLEN,%al//需要读出的扇区数量
		int $0x13
		jnc ok_load_setup//进位标志CF为0时就跳转
		mov $0x0000,%dx
		mov $0x0000,%ax
		int $0x13
		jmp load_setup
ok_load_setup:
load_system:
mov $0x1000,%ax	//将es段寄存器设置为0x1000
mov %ax,%es
		movb $0x00,%dh//磁头号0
		movb $0x00,%dl//驱动器号0
		mov $0x0006,%cx//开始扇区
		mov $0x0000,%bx//es:bx指向缓冲区
		movb $0x02,%ah//0x02,读磁盘扇区到内存
		movb $0x10,%al//需要读出的扇区数量
		int $0x13
		jnc ok_load_system//进位标志CF为0时就跳转
		mov $0x0000,%dx
		mov $0x0000,%ax
		int $0x13
		jmp load_system
ok_load_system:
		jmpl $SETUPSEG,$0
    
    
              
loop0:/*无限循环*/  
    jmp loop0  
      
DispStr:  
    mov $msg   ,%ax  
    mov %ax    ,%bp/*es:bp = 串地址*/  
    mov $12    ,%cx/*cs = 串长度*/  
    mov $0x1301,%ax/*ah=13是功能号表示显示字符串 ,al=01是显示输出方式*/  
    mov $0x000c,%bx/*bh=0是0页,bl=0ch高亮 黑底红字*/  
    mov $0     ,%dl/*0行0列*/  
      
    int $0x10  
    ret  
      
      
.org 0x1fe, 0x90   
.word 0xaa55