段寄存器&段描述符拆分练习
段寄存器16位 + 段描述符高速缓存80位 = 96位
数据结构：
struct Segment
{
WORD Selector; //段选择子
WORD Attrribute; //段属性
DWORD Base; //段基址
DWORD Limit; //段极限
}
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
}
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