1 /*
2 * Copyright (c) 1994 William F. Jolitz.
3 * 386BSD Copyright Restrictions Apply. All Other Rights Reserved.
4 *
5 * $Id: segments.h,v 1.1 94/10/19 17:40:05 bill Exp $
6 *
7 * 386 Segmentation Data Structures and definitions.
8 */
9
10 /*
11 * Selectors
12 */
13 typedef u_short sel_t;
14 #include "sel.h"
15
16 #define ISLDT(s) ((s) & SEL_LDT) /* is it local or global */
17 #define SEL_LDT 4 /* local descriptor table */
18 #define IDXSEL(s) (((s)>>3) & 0x1fff) /* index of selector */
19 #define LSEL(s, r) (((s)<<3) | SEL_LDT | r) /* a local selector */
20 #define GSEL(s, r) (((s)<<3) | r) /* a global selector */
21
22 /*
23 * Memory and System segment descriptors
24 */
25 struct segment_descriptor {
26 unsigned __PACK(sd_lolimit:16); /* segment extent (lsb) */
27 unsigned __PACK(sd_lobase:24); /* segment base address (lsb) */
28 unsigned __PACK(sd_type:5); /* segment type */
29 unsigned __PACK(sd_dpl:2); /* segment descriptor priority level */
30 unsigned __PACK(sd_p:1); /* segment descriptor present */
31 unsigned __PACK(sd_hilimit:4); /* segment extent (msb) */
32 unsigned __PACK(sd_xx:2); /* unused */
33 unsigned __PACK(sd_def32:1); /* default 32 vs 16 bit size */
34 unsigned __PACK(sd_gran:1); /* limit granularity (byte/page units)*/
35 unsigned __PACK(sd_hibase:8); /* segment base address (msb) */
36 } ;
37
38 /*
39 * Gate descriptors (e.g. indirect descriptors)
40 */
41 struct gate_descriptor {
42 unsigned __PACK(gd_looffset:16); /* gate offset (lsb) */
43 unsigned __PACK(gd_selector:16); /* gate segment selector */
44 unsigned __PACK(gd_stkcpy:5); /* number of stack wds to cpy */
45 unsigned __PACK(gd_xx:3); /* unused */
46 unsigned __PACK(gd_type:5); /* segment type */
47 unsigned __PACK(gd_dpl:2); /* segment descriptor priority level */
48 unsigned __PACK(gd_p:1); /* segment descriptor present */
49 unsigned __PACK(gd_hioffset:16); /* gate offset (msb) */
50 } ;
51
52 /*
53 * Generic descriptor
54 */
55 union descriptor {
56 struct segment_descriptor sd;
57 struct gate_descriptor gd;
58 };
59
60 /* system segments and gate types */
61 #define SDT_SYSNULL 0 /* system null */
62 #define SDT_SYS286TSS 1 /* system 286 TSS available */
63 #define SDT_SYSLDT 2 /* system local descriptor table */
64 #define SDT_SYS286BSY 3 /* system 286 TSS busy */
65 #define SDT_SYS286CGT 4 /* system 286 call gate */
66 #define SDT_SYSTASKGT 5 /* system task gate */
67 #define SDT_SYS286IGT 6 /* system 286 interrupt gate */
68 #define SDT_SYS286TGT 7 /* system 286 trap gate */
69 #define SDT_SYSNULL2 8 /* system null again */
70 #define SDT_SYS386TSS 9 /* system 386 TSS available */
71 #define SDT_SYSNULL3 10 /* system null again */
72 #define SDT_SYS386BSY 11 /* system 386 TSS busy */
73 #define SDT_SYS386CGT 12 /* system 386 call gate */
74 #define SDT_SYSNULL4 13 /* system null again */
75 #define SDT_SYS386IGT 14 /* system 386 interrupt gate */
76 #define SDT_SYS386TGT 15 /* system 386 trap gate */
77
78 /* memory segment types */
79 #define SDT_MEMRO 16 /* memory read only */
80 #define SDT_MEMROA 17 /* memory read only accessed */
81 #define SDT_MEMRW 18 /* memory read write */
82 #define SDT_MEMRWA 19 /* memory read write accessed */
83 #define SDT_MEMROD 20 /* memory read only expand dwn limit */
84 #define SDT_MEMRODA 21 /* memory read only expand dwn limit accessed */
85 #define SDT_MEMRWD 22 /* memory read write expand dwn limit */
86 #define SDT_MEMRWDA 23 /* memory read write expand dwn limit acessed */
87 #define SDT_MEME 24 /* memory execute only */
88 #define SDT_MEMEA 25 /* memory execute only accessed */
89 #define SDT_MEMER 26 /* memory execute read */
90 #define SDT_MEMERA 27 /* memory execute read accessed */
91 #define SDT_MEMEC 28 /* memory execute only conforming */
92 #define SDT_MEMEAC 29 /* memory execute only accessed conforming */
93 #define SDT_MEMERC 30 /* memory execute read conforming */
94 #define SDT_MEMERAC 31 /* memory execute read accessed conforming */
95
96 /* is memory segment descriptor pointer ? */
97 #define ISMEMSDP(s) ((s->d_type) >= SDT_MEMRO && (s->d_type) <= SDT_MEMERAC)
98
99 /* is 286 gate descriptor pointer ? */
100 #define IS286GDP(s) (((s->d_type) >= SDT_SYS286CGT \
101 && (s->d_type) < SDT_SYS286TGT))
102
103 /* is 386 gate descriptor pointer ? */
104 #define IS386GDP(s) (((s->d_type) >= SDT_SYS386CGT \
105 && (s->d_type) < SDT_SYS386TGT))
106
107 /* is gate descriptor pointer ? */
108 #define ISGDP(s) (IS286GDP(s) || IS386GDP(s))
109
110 /* is segment descriptor pointer ? */
111 #define ISSDP(s) (ISMEMSDP(s) || !ISGDP(s))
112
113 /* is system segment descriptor pointer ? */
114 #define ISSYSSDP(s) (!ISMEMSDP(s) && !ISGDP(s))
115
116 /*
117 * Software definitions are in this convenient format,
118 * which are translated into inconvenient segment descriptors
119 * when needed to be used by the 386 hardware
120 */
121
122 struct soft_segment_descriptor {
123 unsigned ssd_base ; /* segment base address */
124 unsigned ssd_limit ; /* segment extent */
125 unsigned ssd_type:5 ; /* segment type */
126 unsigned ssd_dpl:2 ; /* segment descriptor priority level */
127 unsigned ssd_p:1 ; /* segment descriptor present */
128 unsigned ssd_xx:4 ; /* unused */
129 unsigned ssd_xx1:2 ; /* unused */
130 unsigned ssd_def32:1 ; /* default 32 vs 16 bit size */
131 unsigned ssd_gran:1 ; /* limit granularity (byte/page units)*/
132 };
133
134 void ssdtosd(struct soft_segment_descriptor *, union descriptor *);
135
136 /*
137 * region descriptors, used to load gdt/idt tables before segments yet exist.
138 */
139 struct region_descriptor {
140 unsigned __PACK(rd_limit:16); /* segment extent */
141 unsigned __PACK(rd_base:32); /* base address */
142 };
143
144 /* load global descriptor table */
145 #define lgdt(s) ({ \
146 struct region_descriptor rd = s; \
147 asm volatile (" \
148 lgdt %0 ; \
149 /* flush prefetch queue */ \
150 jmp 1f ; nop ; 1: \
151 /* reload stale selectors */ \
152 movw %w1, %%ds ; movw %w1, %%es ; movw %w1, %%ss ; \
153 /* reload code selector by using an intersegmental return */ \
154 pushl %2 ; pushl $1f ; lret ; 1: " \
155 : : "m"(rd), "r"(KDSEL), "r"(KCSEL)); \
156 })
157
158 /* load interrupt descriptor table */
159 #define lidt(s) ({ \
160 struct region_descriptor rd = s; \
161 asm volatile ("lidt %0 " : : "m"(rd)); \
162 })
163
164 /* load local descriptor table */
165 #define lldt(s) ({ \
166 sel_t sel = s; \
167 asm volatile ("lldt %w0 " : : "r"(sel)); \
168 })
169
170 /* load current task state */
171 #define ltr(s) ({ \
172 sel_t sel = s; \
173 asm volatile ("ltr %w0 " : : "r"(sel)); \
174 })
175
176 /*
177 * Segment Protection Exception code bits
178 */
179
180 #define SEGEX_EXT 0x01 /* recursive or externally induced */
181 #define SEGEX_IDT 0x02 /* interrupt descriptor table */
182 #define SEGEX_TI 0x04 /* local descriptor table */
183 /* other bits are affected descriptor index */
184 #define SEGEX_IDX(s) ((s)>>3)&0x1fff)
185
186 /*
187 * Size of IDT table
188 */
189
190 #define NIDT 256
191 #define NRSVIDT 32 /* reserved entries for cpu exceptions */
192
193 /* special selectors in the kernel */
194 extern sel_t _udatasel, _ucodesel, _exit_tss_sel;
195
196 /* global descriptor table */
197 extern union descriptor *gdt, gdt_bootstrap[];
198
199 /* global descriptor table allocation pointers/counters */
200 extern struct segment_descriptor *sdfirstp_gdesc, *sdlast_gdesc,
201 *sdlastfree_gdesc;
202 extern int sdngd_gdesc, sdnfree_gdesc;
203
204 void expanddesctable(void);
205
206 /*
207 * Allocate a global descriptor to the kernel. If no free descriptors,
208 * expand the table.
209 */
210 extern inline struct segment_descriptor *
allocdesc(void)211 allocdesc(void)
212 {
213 struct segment_descriptor *sdp;
214 int fullsearch = 1;
215
216 tryagain:
217 /* out of global descriptors? then, make more */
218 if (sdnfree_gdesc == 0)
219 expanddesctable();
220
221 /* find a free descriptor, starting with last freed descriptor */
222 for (sdp = sdlastfree_gdesc; sdp <= sdlast_gdesc && sdp->sd_p ; sdp++)
223 ;
224
225 /* if did not find a descriptor, start at beginning of table again */
226 if (sdp > sdlast_gdesc && fullsearch) {
227 sdlastfree_gdesc = sdfirstp_gdesc;
228 fullsearch = 0;
229 goto tryagain;
230 }
231
232 #ifdef DIAGNOSTIC
233 if(sdp->sd_p)
234 panic("allocdesc: no free descriptor");
235 #endif
236
237 /* next place to try? */
238 if (sdp < sdlast_gdesc)
239 sdlastfree_gdesc = sdp + 1;
240 sdnfree_gdesc--;
241
242 /* fill in the blanks */
243 /* memset(sdp, 0, sizeof(*sdp)); /* XXX overkill */
244 *(int *) sdp = 0; /* clear lower word */
245 *(((int *) sdp) + 1) = 0; /* clear upper word */
246 sdp->sd_p = 1;
247 return (sdp);
248 }
249
250 /*
251 * Return a Global descriptor to free status, so it may be reused.
252 */
253 extern inline void
freedesc(struct segment_descriptor * sdp)254 freedesc(struct segment_descriptor *sdp)
255 {
256 sdp->sd_p = 0; /* will generate an invalid tss if used */
257 sdnfree_gdesc++;
258 if (sdlastfree_gdesc > sdp)
259 sdlastfree_gdesc = sdp;
260 /* XXX reduce table size if nfreedesc grows to larger than half of
261 total table side, and if we can compact the table. when we have
262 a surplus of descriptors, restrict allocation to first half, and
263 keep seperate counts on still allocated upper/lower halfs. We can
264 shrink the table by half when the outstanding allocated descriptors
265 in the top half drops to zero -- too hard for now. */
266 }
267
268
269 #ifdef _PROC_H_
270 /*
271 * Allocate a TSS descriptor to a kernel thread, in the course of
272 * creating a new thread. Special version of allocdesc().
273 */
274 extern inline
alloctss(struct proc * p)275 alloctss(struct proc *p) {
276 struct segment_descriptor *sdp = allocdesc();
277 sdp->sd_lolimit = sizeof(struct i386tss) - 1;
278 sdp->sd_lobase = (int)p->p_addr;
279 sdp->sd_hibase = ((int)p->p_addr) >> 24;
280 sdp->sd_type = SDT_SYS386TSS;
281
282 /* construct selector for new tss */
283 p->p_md.md_tsel = GSEL((sdp - &gdt[0].sd), SEL_KPL);
284 }
285 #endif
286
287 /*
288 * Return to the free pool the TSS descriptor of a thread being
289 * deallocated. Special case of freedesc().
290 */
291 extern inline void
freetss(sel_t tss_sel)292 freetss(sel_t tss_sel) {
293
294 /*
295 * if running on this thread, change to a interim
296 * tss until we swtch()
297 */
298 /* if (tss_sel == str()) */
299 ltr(_exit_tss_sel); /* busy until final ljmp */
300
301 freedesc(&gdt[IDXSEL(tss_sel)].sd);
302 }
303