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
|
#include <stdio.h>
#include <stdint.h>
/*
// structure to be encoded at encodeGdtEntry()
struct GDT
{
uint32_t base;
uint32_t limit;
uint8_t access_byte;
uint8_t flags;
};
GDT strnulldesc {0, 0, 0, 0};
GDT strkernelcode {0, 0xFFFFF, 0x9A, 0xC};
GDT strkerneldata {0, 0xFFFFF, 0x92, 0xC};
GDT strusercode {0, 0xFFFFF, 0xFA, 0xC};
GDT struserdata {0, 0xFFFFF, 0xF2, 0xC};
uint8_t* nulldesc;
uint8_t* kernelcode;
uint8_t* kerneldata;
uint8_t* usercode;
uint8_t* userdata;
void encodeGdtEntry(uint8_t *target, struct GDT source)
{
// Check the limit to make sure that it can be encoded
if (source.limit > 0xFFFFF) {printf("GDT cannot encode limits larger than 0xFFFFF\n");}
// Encode the limit
target[0] = source.limit & 0xFF;
target[1] = (source.limit >> 8) & 0xFF;
target[6] = (source.limit >> 16) & 0x0F;
// Encode the base
target[2] = source.base & 0xFF;
target[3] = (source.base >> 8) & 0xFF;
target[4] = (source.base >> 16) & 0xFF;
target[7] = (source.base >> 24) & 0xFF;
// Encode the access byte
target[5] = source.access_byte;
// Encode the flags
target[6] |= (source.flags << 4);
}
extern "C" void setupGdt() {
} */
|