2015-03-13 22:44:25 +08:00
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#define Descriptor(base,lim,type)\
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.word lim&0xffff;\
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.word base&0xffff;\
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.byte (base>>16)&0xff;\
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.word ((lim>>8)&0xf00)|(type&0x0f0ff);\
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.byte ((base>>24)&0xff)
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DA_C = 0x98
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DA_32 = 0x4000
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DA_DRW = 0x92
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.text
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.globl start
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.code16
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start:
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jmpl $0x0, $code
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GDT_START:
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2015-03-14 00:17:50 +08:00
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Descriptor_DUMMY:Descriptor(0x0,0x0,0x0) /* 第0项里面全是0，不会用到 */
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Descript_CODE32 :Descriptor(0x0,0xffffffff,DA_C+DA_32) /* 32位代码段的段基址，段界限，访问类型 */
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Descriptor_VIDEO:Descriptor(0xb8000,0x0ffff,DA_DRW) /* 显存的段基址，段界限，访问类型 */
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2015-03-13 22:44:25 +08:00
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GDT_END:
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GdtPtr:
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.word (GDT_END-GDT_START)-1 # so does gdt
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.long GDT_START # This will be rewrite by code.
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msg:
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.string "Hello world!"
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code:
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mov %cs,%ax
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mov %ax,%ds
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mov %ax,%es
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mov %ax,%ss
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mov $0x8000,%sp
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/*显示HelloWorld字符串*/
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mov $msg ,%ax
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mov %ax ,%bp
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mov $12 ,%cx
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mov $0x1301,%ax
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mov $0x000c,%bx
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mov $0 ,%dl
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int $0x10
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/*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*/
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lgdt GdtPtr
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/*关中断*/
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cli
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/*打开地址线A20*/
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inb $0x92,%al
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or $0x02,%al
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outb %al,$0x92
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/*设置cr0寄存器,切换到保护模式*/
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movl %cr0,%eax
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or $1,%eax
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movl %eax,%cr0
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/*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*/
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ljmp $0x8,$(LABEL_SEG_CODE32)
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/*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*/
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LABEL_SEG_CODE32:
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.align 32
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.code32
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movw $0x10,%ax
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movw %ax,%gs
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movl $((80*11+79)*2),%edi/*第11行，79列*/
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movb $0x0c,%ah/*高四位表示黑底,低四位表示红字*/
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movb $'P',%al/*显示的字符*/
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movw %ax,%gs:(%edi)
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loop2:
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jmp loop2
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.org 0x1fe, 0x90
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.word 0xaa55
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