1 #include <string.h>

2 #include "segm.h"

3

4 #define BIT_ACCESSED (1 << 8)

5 #define BIT_WR (1 << 9)

6 #define BIT_RD (1 << 9)

7 #define BIT_EXP_DOWN (1 << 10)

8 #define BIT_CONFORMING (1 << 10)

9 #define BIT_CODE (1 << 11)

10 #define BIT_NOSYS (1 << 12)

11 #define BIT_PRESENT (1 << 15)

12

13 #define BIT_BIG (1 << 6)

14 #define BIT_DEFAULT (1 << 6)

15 #define BIT_GRAN (1 << 7)

16

17 enum {TYPE_DATA, TYPE_CODE};

18

19 static void segm_desc(desc_t *desc, uint32_t base, uint32_t limit, int dpl, int type);

20

21

22 static desc_t gdt[4];

23

24

25 void init_segm(void)

26 {

27 memset(gdt, 0, sizeof gdt);

28 segm_desc(gdt + SEGM_KCODE, 0, 0xffffffff, 0, TYPE_CODE);

29 segm_desc(gdt + SEGM_KDATA, 0, 0xffffffff, 0, TYPE_DATA);

30

31 set_gdt((uint32_t)gdt, sizeof gdt - 1);

32

33 setup_selectors(selector(SEGM_KCODE, 0), selector(SEGM_KDATA, 0));

34 }

35

36 uint16_t selector(int idx, int rpl)

37 {

38 return (idx << 3) | (rpl & 3);

39 }

40

41 static void segm_desc(desc_t *desc, uint32_t base, uint32_t limit, int dpl, int type)

42 {

43 desc->d[0] = limit & 0xffff; /* low order 16bits of limit */

44 desc->d[1] = base & 0xffff; /* low order 16bits of base */

45

46 /* third 16bit part contains the last 8 bits of base, the 2 priviledge

47 * level bits starting on bit 13, present flag on bit 15, and type bits

48 * starting from bit 8

49 */

50 desc->d[2] = ((base >> 16) & 0xff) | ((dpl & 3) << 13) | BIT_PRESENT |

51 BIT_NOSYS | (type == TYPE_DATA ? BIT_WR : (BIT_RD | BIT_CODE));

52

53 /* last 16bit part contains the last nibble of limit, the last byte of

54 * base, and the granularity and deafult/big flags in bits 23 and 22 resp.

55 */

56 desc->d[3] = ((limit >> 16) & 0xf) | ((base >> 16) & 0xff00) | BIT_GRAN | BIT_BIG;

57 }