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
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
|
#ifndef GDT_H
#define GDT_H
#include <stdint.h>
#include <string.h>
#define GDT_ENTRY_SIZE 0x8
#define GDT_NULL_SEGMENT 0x0
#define GDT_KERNEL_CODE_SEGMENT 0x1
#define GDT_KERNEL_DATA_SEGMENT 0x2
#define GDT_USERMODE_CODE_SEGMENT 0x3
#define GDT_USERMODE_DATA_SEGMENT 0x4
#define GDT_TSS_SEGMENT 0x5
struct GDT_Entry
{
uint16_t limit_low;
uint32_t base_low : 24;
uint32_t accessed : 1;
uint32_t read_write : 1; // readable for code, writable for data
uint32_t conforming_expand_down : 1; // conforming for code, expand down for data
uint32_t code : 1; // 1 for code, 0 for data
uint32_t code_data_segment : 1; // should be 1 for everything but TSS and LDT
uint32_t DPL : 2; // privilege level
uint32_t present : 1;
uint32_t limit_high : 4;
uint32_t available : 1; // only used in software; has no effect on hardware
uint32_t long_mode : 1;
uint32_t big : 1; // 32-bit opcodes for code, uint32_t stack for data
uint32_t gran : 1; // 1 to use 4k page addressing, 0 for byte addressing
uint8_t base_high;
}__attribute__((packed));
typedef struct GDT_Pointer
{
uint16_t size;
uint32_t offset;
}__attribute__((packed)) GDT_Pointer;
struct tss_entry_struct
{
uint32_t prev_tss; // The previous TSS - with hardware task switching these form a kind of backward linked list.
uint32_t esp0; // The stack pointer to load when changing to kernel mode.
uint32_t ss0; // The stack segment to load when changing to kernel mode.
// Everything below here is unused.
uint32_t esp1; // esp and ss 1 and 2 would be used when switching to rings 1 or 2.
uint32_t ss1;
uint32_t esp2;
uint32_t ss2;
uint32_t cr3;
uint32_t eip;
uint32_t eflags;
uint32_t eax;
uint32_t ecx;
uint32_t edx;
uint32_t ebx;
uint32_t esp;
uint32_t ebp;
uint32_t esi;
uint32_t edi;
uint32_t es;
uint32_t cs;
uint32_t ss;
uint32_t ds;
uint32_t fs;
uint32_t gs;
uint32_t ldt;
uint16_t trap;
uint16_t iomap_base;
} __attribute__((packed));
void gdt_init();
uint8_t gen_access_byte(uint8_t priv, uint8_t s, uint8_t ex, uint8_t dc, uint8_t rw);
uint64_t gen_gdt_entry(uint32_t base, uint32_t limit, uint8_t access_byte, uint8_t flag);
uint8_t gen_flag(uint8_t gr, uint8_t sz);
#endif
|
