80x86描述符总结

一、描述符的分类

二、描述符格式

1、数据段描述符

2、代码段描述符

3、LDT段描述符

4、TSS段描述符

5、调用门描述符

6、中断门描述符

7、陷阱门描述符

8、任务门描述符

三、解析描述符的小程序

#include <stdio.h>//定义描述符中的低32位struct seg_des_low_word{    unsigned int limit_0_15:16;    unsigned int base_0_15 :16;};//定义描述符中的高32位(通用格式)struct seg_des_high_word{    unsigned int base_16_23 :8;    unsigned int type       :4;    unsigned int s          :1;    unsigned int dpl        :2;    unsigned int p          :1;    unsigned int limit_16_19:4;    unsigned int avl        :1;    unsigned int l          :1;//保留给64位处理器使用    unsigned int d_b        :1;    unsigned int g          :1;    unsigned int base_24_31 :8;};void parse_seg_des(unsigned int low_dw, unsigned int hig_dw){    struct seg_des_low_word *pl         =(struct seg_des_low_word*)&low_dw;    struct seg_des_high_word *ph        =(struct seg_des_high_word*)&hig_dw;    unsigned int type = ph->type;    int offset = (hig_dw & 0xFFFF0000) | (low_dw & 0x0000FFFF);    unsigned int seg_base =         (ph->base_24_31<<24)|(ph->base_16_23<<16)|pl->base_0_15;//拼接基地址字段    unsigned int seg_limit =        seg_limit = (ph->limit_16_19<<16)|pl->limit_0_15;//拼接段限长字段    int system = ph->s;    //下面的字段输出是不是很方便？这就是位字段的好处之一    printf("P = %d\n",ph->p);    printf("DPL = %d\n",ph->dpl); //P和DPL是每个段描述符都有的    if(system == 0) //system segment    {        //TSS or LDT        if(type == 9 || type==11 || type==2)   //==的优先级高于||        {            //print base address,limit,G            printf("base address = %#X\n",seg_base);            printf("limit = %#X ，",seg_limit);            if(ph->g == 1)                printf("以4KB为单位\n");            else                printf("以B为单位\n");        }        if(type == 9)            printf("TSS段，不忙\n");        else if(type == 11)            printf("TSS段，忙\n");         else if(type == 5)            printf("任务门，TSS段选择子 = %#X\n",pl->base_0_15);        else if(type == 6)            printf("16位中断门，段选择子 = %#X，偏移 = %#X\n",pl->base_0_15,offset);        else if(type == 14)            printf("32位中断门，段选择子 = %#X，偏移 = %#X\n",pl->base_0_15,offset);        else if(type == 7)            printf("16位陷阱门，段选择子 = %#X，偏移 = %#X\n",pl->base_0_15,offset);        else if(type == 15)            printf("32位陷阱门，段选择子 = %#X，偏移 = %#X\n",pl->base_0_15,offset);        else if(type == 12)            printf("调用门，段选择子 = %#X，偏移 = %#X , 参数个数 = %d\n",pl->base_0_15,offset, high_word & 0x1F);        else if(type == 2)            printf("LDT描述符\n");    }    else //data or code segment    {        printf("base address = %#X\n",seg_base);        printf("limit = %#X ，",seg_limit);        if(ph->g == 1)            printf("以4KB为单位\n");        else            printf("以B为单位\n");        if(type & 0x08 ) //代码段，分析C，R，D              {            printf("代码段，");            if(ph->d_b == 1) //D=1                printf("默认操作数大小为32位\n");            else                printf("默认操作数大小为16位\n");            if(type & 0x04) //C=1                printf("一致性，");            else                printf("非一致性，");            if(type & 0x02) //R=1                printf("可读\n");            else                printf("不可读\n");        }        else    //数据段，分析B，E，W        {            printf("数据段，");            if(ph->d_b == 1) //B=1                printf("栈段使用ESP，ESP最大为0xFFFFFFFF\n");            else                printf("栈段使用SP，SP最大为0xFFFF\n");            if(type & 0x04) //E=1                printf("向下扩展，");            else                printf("向上扩展，");            if(type & 0x02) //W=1                printf("可写\n");            else                printf("不可写\n");        }    }}int main(void){    printf("please input the segment descriptor,format: [low dword] [high dword]\n");    printf("example:\n");    printf("000003ff 00c0fa00\n");    unsigned int l_dword = 0;    unsigned int h_dword = 0;    //请求用户输入描述符，先是低32位，再是高32位    scanf("%x" "%x",&l_dword,&h_dword);     parse_seg_des(l_dword,h_dword);    return 0;}