kern
view src/segm.c @ 55:88a6c4e192f9
Fixed most important task switching bugs.
Now it seems that I can switch in and out of user space reliably.
| author | John Tsiombikas <nuclear@member.fsf.org> |
|---|---|
| date | Mon, 15 Aug 2011 04:03:39 +0300 |
| parents | 4eaecb14fe31 |
| children |
line source
1 #include <string.h>
2 #include "segm.h"
3 #include "desc.h"
4 #include "tss.h"
6 /* bits for the 3rd 16bt part of the descriptor */
7 #define BIT_ACCESSED (1 << 8)
8 #define BIT_WR (1 << 9)
9 #define BIT_RD (1 << 9)
10 #define BIT_EXP_DOWN (1 << 10)
11 #define BIT_CONFORMING (1 << 10)
12 #define BIT_CODE (1 << 11)
13 #define BIT_NOSYS (1 << 12)
14 #define BIT_PRESENT (1 << 15)
15 /* TSS busy bit */
16 #define BIT_BUSY (1 << 9)
18 /* bits for the last 16bit part of the descriptor */
19 #define BIT_BIG (1 << 6)
20 #define BIT_DEFAULT (1 << 6)
21 #define BIT_GRAN (1 << 7)
23 enum {TYPE_DATA, TYPE_CODE};
25 /* we need the following bit pattern at the 8th bit excluding the busy bit: 1001 */
26 #define TSS_TYPE_BITS (9 << 8)
28 static void segm_desc(desc_t *desc, uint32_t base, uint32_t limit, int dpl, int type);
29 static void task_desc(desc_t *desc, uint32_t base, uint32_t limit, int dpl);
31 /* these functions are implemented in segm-asm.S */
32 void setup_selectors(uint16_t code, uint16_t data);
33 void set_gdt(uint32_t addr, uint16_t limit);
34 void set_task_reg(uint16_t tss_selector);
37 /* our global descriptor table */
38 static desc_t gdt[6];
41 void init_segm(void)
42 {
43 memset(gdt, 0, sizeof gdt);
44 segm_desc(gdt + SEGM_KCODE, 0, 0xffffffff, 0, TYPE_CODE);
45 segm_desc(gdt + SEGM_KDATA, 0, 0xffffffff, 0, TYPE_DATA);
46 segm_desc(gdt + SEGM_UCODE, 0, 0xffffffff, 3, TYPE_CODE);
47 segm_desc(gdt + SEGM_UDATA, 0, 0xffffffff, 3, TYPE_DATA);
49 set_gdt((uint32_t)gdt, sizeof gdt - 1);
51 setup_selectors(selector(SEGM_KCODE, 0), selector(SEGM_KDATA, 0));
52 }
54 /* constructs a GDT selector based on index and priviledge level */
55 uint16_t selector(int idx, int rpl)
56 {
57 return (idx << 3) | (rpl & 3);
58 }
60 void set_tss(uint32_t addr)
61 {
62 task_desc(gdt + SEGM_TASK, addr, sizeof(struct task_state) - 1, 3);
63 set_task_reg(selector(SEGM_TASK, 0));
64 }
66 static void segm_desc(desc_t *desc, uint32_t base, uint32_t limit, int dpl, int type)
67 {
68 desc->d[0] = limit & 0xffff; /* low order 16bits of limit */
69 desc->d[1] = base & 0xffff; /* low order 16bits of base */
71 /* third 16bit part contains the last 8 bits of base, the 2 priviledge
72 * level bits starting on bit 13, present flag on bit 15, and type bits
73 * starting from bit 8
74 */
75 desc->d[2] = ((base >> 16) & 0xff) | ((dpl & 3) << 13) | BIT_PRESENT |
76 BIT_NOSYS | (type == TYPE_DATA ? BIT_WR : (BIT_RD | BIT_CODE));
78 /* last 16bit part contains the last nibble of limit, the last byte of
79 * base, and the granularity and deafult/big flags in bits 23 and 22 resp.
80 */
81 desc->d[3] = ((limit >> 16) & 0xf) | ((base >> 16) & 0xff00) | BIT_GRAN | BIT_BIG;
82 }
84 static void task_desc(desc_t *desc, uint32_t base, uint32_t limit, int dpl)
85 {
86 desc->d[0] = limit & 0xffff;
87 desc->d[1] = base & 0xffff;
89 desc->d[2] = ((base >> 16) & 0xff) | ((dpl & 3) << 13) | BIT_PRESENT |
90 TSS_TYPE_BITS; /* XXX busy ? */
91 desc->d[3] = ((limit >> 16) & 0xf) | ((base >> 16) & 0xff00) | BIT_GRAN;
92 }
93 /*
94 static void dbg_print_gdt(void)
95 {
96 int i;
98 printf("Global Descriptor Table\n");
99 printf("-----------------------\n");
101 for(i=0; i<6; i++) {
102 print_desc(gdt + i);
103 }
104 }
106 static void print_desc(desc_t *desc)
107 {
108 uint32_t base, limit;
109 int dpl, g, db, l, avl, p, s, type;
110 char *type_str;
112 base = (uint32_t)desc->d[1] | ((uint32_t)(desc->d[2] & 0xff) << 16) | ((uint32_t)(desc->d[3] >> 8) << 24);
113 limit = (uint32_t)desc->d[0] | ((uint32_t)(desc->d[3] & 0xf) << 16);
114 dpl = (desc->d[2] >> 13) & 3;
115 type = (desc->d[2] >> 8) & 0xf;
116 g = (desc->d[3] >> 23) & 1;
117 db = (desc->d[3] >> 22) & 1;
118 l = (desc->d[3] >> 21) & 1;
119 avl = (desc->d[3] >> 20) & 1;
121 p = (desc->d[2] >> 15) & 1;
122 s = (desc->d[2] >> 12) & 1;
123 }
124 */