段寄存器&段描述符拆分练习

31c3245eda217bdff2221cf5faf3fd9b.png

段寄存器16位 + 段描述符高速缓存80位 = 96位

数据结构：

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struct Segment 
{
    WORD Selector;	//段选择子
    WORD Attrribute;	//段属性
    DWORD Base;		//段基址
    DWORD Limit;	//段极限
}
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环境：Win7 x32
CS=1B

段描述符：00cf9300`0000ffff

Base 31:24
0000 0000 = 0

G  D/B  L  AVL
1   1   0   0

Limit 19:16
1111 = F

P	DPL	S	Type
1	00	1	0011

Base 23:16
0000 0000 = 0

//////////////////

Base 31:16
0000 0000 0000 0000 = 0

Limit 15:00
1111 1111 1111 1111 = FFFF

//////////////////

struct Segment 
{
    WORD Selector = 1B = 0001 1011	//段选择子
    WORD Attrribute = 1100 + 1111 + 1001 + 0011 //段描述符高32位的第8位到第23位
    DWORD Base = 0000 0000 0000 0000	//高32位的 31:24 + 7:0 + 低32位的 31:16
    DWORD Limit = FFFFFFFF	//通过段描述符得到FFFFF 由于G位为1，分页粒度为4KB，故Limit = 0xFFFFF*0X1000 + 0xFFF
}
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环境Win7 x32

gdtr = 80b93800
gdtl = 3ff

80b93800  00000000`00000000 00cf9b00`0000ffff
80b93810  00cf9300`0000ffff 00cffb00`0000ffff
80b93820  00cff300`0000ffff 80008bb9`3c0020ab
80b93830  804093b9`60004fff 0040f300`00000fff
80b93840  0000f200`0400ffff 00000000`00000000
80b93850  800089b9`5d200067 800089b9`5cb00067
80b93860  00000000`00000000 00000000`00000000
80b93870  800092b9`380003ff 00000000`00000000
80b93880  00000000`00000000 00000000`00000000
80b93890  00000000`00000000 00000000`00000000
80b938a0  800089b9`5d900067 00000000`00000000
80b938b0  00000000`00000000 00000000`00000000
........  00000000`00000000 00000000`00000000
80b93bf0  00000000`00000000 00000000`00000000


G — Granularity
LIMIT — Segment Limit
P — Segment present
S — Descriptor type (0 = system; 1 = code or data)
TYPE — Segment type
DPL — Descriptor privilege level
AVL — Available for use by system software
BASE — Segment base address
D/B — Default operation size (0 = 16-bit segment; 1 = 32-bit segment)
L — 64-bit code segment (IA-32e mode onl


P  DPL  S
1  0/3  1 = 9/f
当段描述符长这样：
    xxxx9xxx`xxxxxxxx 
或  xxxxfxxx`xxxxxxxx 
的时候为代码段/数据段描述符
故：
gdt[1]  = 00cf9b00`0000ffff		//Code Execute/Read, accessed
gdt[2]  = 00cf9300`0000ffff		//Data Read/Write, accessed
gdt[3]  = 00cffb00`0000ffff		//Code Execute/Read, accessed
gdt[4]  = 00cff300`0000ffff		//Data Read/Write, accessed
gdt[6]  = 804093b9`60004fff		//Data Read/Write, accessed
gdt[7]  = 0040f300`00000fff		//Data Read/Write, accessed
gdt[8]  = 0000f200`0400ffff		//Data Read/Write
gdt[14] = 800092b9`380003ff		//Data Read/Write
共8个其中TYPE<8时为Data段，TYPE>=8时为Code段

Type Field Description
Decimal  11 10  9  8
             E  W  A
0         0  0  0  0 Data Read-Only
1         0  0  0  1 Data Read-Only, accessed
2         0  0  1  0 Data Read/Write
3         0  0  1  1 Data Read/Write, accessed
4         0  1  0  0 Data Read-Only, expand-down
5         0  1  0  1 Data Read-Only, expand-down, accessed
6         0  1  1  0 Data Read/Write, expand-down
7         0  1  1  1 Data Read/Write, expand-down, accessed
             C  R  A
8         1  0  0  0 Code Execute-Only
9         1  0  0  1 Code Execute-Only, accessed
10        1  0  1  0 Code Execute/Read
11        1  0  1  1 Code Execute/Read, accessed
12        1  1  0  0 Code Execute-Only, conforming
13        1  1  0  1 Code Execute-Only, conforming, accessed
14        1  1  1  0 Code Execute/Read, conforming
15        1  1  1  1 Code Execute/Read, conforming, accessed


P  DPL  S
1  0/3  0 = 8/e
当段描述符长这样：
    xxxx8xxx`xxxxxxxx 
或  xxxxexxx`xxxxxxxx 
的时候为系统段描述符
gdt[5]  = 80008bb9`3c0020ab		//32-bit TSS (Busy)
gdt[10] = 800089b9`5d200067		//32-bit TSS (Available)
gdt[11] = 800089b9`5cb00067		//32-bit TSS (Available)
gdt[20] = 800089b9`5d900067		//32-bit TSS (Available)
共4个其中：

Type Field Description
Decimal  11 10  9  8		 32-Bit Mode 				IA-32e Mode
0         0  0  0  0		 Reserved				Reserved
1         0  0  0  1		 16-bit TSS (Available) 		Reserved
2         0  0  1  0		 LDT 					LDT
3         0  0  1  1		 16-bit TSS (Busy) 			Reserved
4         0  1  0  0		 16-bit Call Gate 			Reserved
5         0  1  0  1		 Task Gate 				Reserved
6         0  1  1  0		 16-bit Interrupt Gate 			Reserved
7         0  1  1  1		 16-bit Trap Gate 			Reserved
8         1  0  0  0		 Reserved 				Reserved
9         1  0  0  1		 32-bit TSS (Available) 		64-bit TSS (Available)
10        1  0  1  0		 Reserved 				Reserve
11        1  0  1  1		 32-bit TSS (Busy) 			64-bit TSS (Busy
12        1  1  0  0		 32-bit Call Gate 			64-bit Call Gat
13        1  1  0  1		 Reserved 				Reserve
14        1  1  1  0		 32-bit Interrupt 			Gate 64-bit Interrupt Gate
15        1  1  1  1		 32-bit Trap Gate 			64-bit Trap Gate
内核
#分页
段寄存器&段描述符拆分练习
https://rogxo.github.io/2021/12/08/2021-12-08-段寄存器&段描述符拆分练习/
作者
Rogxo
发布于
2021年12月8日
许可协议
CC BY-NC-SA 4.0