1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
|
#include"../include/types.h"
struct gdt_entry
{
uint16_t limit;
uint16_t base1;
uint8_t base2;
uint8_t access;
uint8_t limit_flags;
uint8_t base3;
} __attribute__((packed));
struct gdt_pointer
{
uint16_t size;
uint32_t offset;
} __attribute__((packed));
// asm function
extern void load_gdt(struct gdt_pointer *gdtp);
struct gdt_entry gdt[5];
struct gdt_pointer gdtp;
void init_gdt_entry(size_t num, uint32_t limit, uint32_t base, uint8_t access, uint8_t limit_flags)
{
gdt[num].limit=limit;
gdt[num].base1=(base & 0xffff);
gdt[num].base2=(base & 0xff0000) >> 16;
gdt[num].access=access;
gdt[num].limit_flags=limit_flags;
gdt[num].base3=(base & 0xff000000) >> 24;
}
void init_gdt_table()
{
gdtp.size=sizeof(gdt)-1;
gdtp.offset=(uint32_t)&gdt;
init_gdt_entry(0,0,0,0,0); // null segment
init_gdt_entry(1,0xffffffff,0,0b10011010,0b11001111); // code segment
init_gdt_entry(2,0xffffffff,0,0b10010010,0b11001111); // data segment
init_gdt_entry(3,0xffffffff,0,0b11111010,0b11001111); // user mode code segment
init_gdt_entry(4,0xffffffff,0,0b11110010,0b11001111); // user mode data segment
load_gdt(&gdtp);
}
|
