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@ -0,0 +1,81 @@ |
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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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Descriptor_DUMMY:Descriptor(0x0,0x0,0x0) |
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Descript_CODE32 :Descriptor(0x0,0xffffffff,DA_C+DA_32) |
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Descriptor_VIDEO:Descriptor(0xb8000,0x0ffff,DA_DRW) |
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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 |
yuchen