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5a0015d6 CZ |
1 | /* |
2 | * arch/xtensa/kernel/vectors.S | |
3 | * | |
4 | * This file contains all exception vectors (user, kernel, and double), | |
5 | * as well as the window vectors (overflow and underflow), and the debug | |
6 | * vector. These are the primary vectors executed by the processor if an | |
7 | * exception occurs. | |
8 | * | |
9 | * This file is subject to the terms and conditions of the GNU General | |
10 | * Public License. See the file "COPYING" in the main directory of | |
11 | * this archive for more details. | |
12 | * | |
13 | * Copyright (C) 2005 Tensilica, Inc. | |
14 | * | |
15 | * Chris Zankel <chris@zankel.net> | |
16 | * | |
17 | */ | |
18 | ||
19 | /* | |
20 | * We use a two-level table approach. The user and kernel exception vectors | |
21 | * use a first-level dispatch table to dispatch the exception to a registered | |
22 | * fast handler or the default handler, if no fast handler was registered. | |
23 | * The default handler sets up a C-stack and dispatches the exception to a | |
24 | * registerd C handler in the second-level dispatch table. | |
25 | * | |
26 | * Fast handler entry condition: | |
27 | * | |
28 | * a0: trashed, original value saved on stack (PT_AREG0) | |
29 | * a1: a1 | |
30 | * a2: new stack pointer, original value in depc | |
31 | * a3: dispatch table | |
32 | * depc: a2, original value saved on stack (PT_DEPC) | |
33 | * excsave_1: a3 | |
34 | * | |
35 | * The value for PT_DEPC saved to stack also functions as a boolean to | |
36 | * indicate that the exception is either a double or a regular exception: | |
37 | * | |
38 | * PT_DEPC >= VALID_DOUBLE_EXCEPTION_ADDRESS: double exception | |
39 | * < VALID_DOUBLE_EXCEPTION_ADDRESS: regular exception | |
40 | * | |
41 | * Note: Neither the kernel nor the user exception handler generate literals. | |
42 | * | |
43 | */ | |
44 | ||
45 | #include <linux/linkage.h> | |
46 | #include <asm/ptrace.h> | |
5a0015d6 | 47 | #include <asm/current.h> |
0013a854 | 48 | #include <asm/asm-offsets.h> |
5a0015d6 CZ |
49 | #include <asm/pgtable.h> |
50 | #include <asm/processor.h> | |
51 | #include <asm/page.h> | |
52 | #include <asm/thread_info.h> | |
5a0015d6 | 53 | |
173d6681 CZ |
54 | #define WINDOW_VECTORS_SIZE 0x180 |
55 | ||
5a0015d6 CZ |
56 | |
57 | /* | |
58 | * User exception vector. (Exceptions with PS.UM == 1, PS.EXCM == 0) | |
59 | * | |
60 | * We get here when an exception occurred while we were in userland. | |
61 | * We switch to the kernel stack and jump to the first level handler | |
62 | * associated to the exception cause. | |
63 | * | |
64 | * Note: the saved kernel stack pointer (EXC_TABLE_KSTK) is already | |
65 | * decremented by PT_USER_SIZE. | |
66 | */ | |
67 | ||
68 | .section .UserExceptionVector.text, "ax" | |
69 | ||
70 | ENTRY(_UserExceptionVector) | |
71 | ||
bc5378fc MF |
72 | xsr a3, excsave1 # save a3 and get dispatch table |
73 | wsr a2, depc # save a2 | |
5a0015d6 CZ |
74 | l32i a2, a3, EXC_TABLE_KSTK # load kernel stack to a2 |
75 | s32i a0, a2, PT_AREG0 # save a0 to ESF | |
bc5378fc | 76 | rsr a0, exccause # retrieve exception cause |
5a0015d6 CZ |
77 | s32i a0, a2, PT_DEPC # mark it as a regular exception |
78 | addx4 a0, a0, a3 # find entry in table | |
79 | l32i a0, a0, EXC_TABLE_FAST_USER # load handler | |
80 | jx a0 | |
81 | ||
82 | /* | |
83 | * Kernel exception vector. (Exceptions with PS.UM == 0, PS.EXCM == 0) | |
84 | * | |
85 | * We get this exception when we were already in kernel space. | |
86 | * We decrement the current stack pointer (kernel) by PT_SIZE and | |
87 | * jump to the first-level handler associated with the exception cause. | |
88 | * | |
89 | * Note: we need to preserve space for the spill region. | |
90 | */ | |
91 | ||
92 | .section .KernelExceptionVector.text, "ax" | |
93 | ||
94 | ENTRY(_KernelExceptionVector) | |
95 | ||
bc5378fc MF |
96 | xsr a3, excsave1 # save a3, and get dispatch table |
97 | wsr a2, depc # save a2 | |
5a0015d6 CZ |
98 | addi a2, a1, -16-PT_SIZE # adjust stack pointer |
99 | s32i a0, a2, PT_AREG0 # save a0 to ESF | |
bc5378fc | 100 | rsr a0, exccause # retrieve exception cause |
5a0015d6 CZ |
101 | s32i a0, a2, PT_DEPC # mark it as a regular exception |
102 | addx4 a0, a0, a3 # find entry in table | |
103 | l32i a0, a0, EXC_TABLE_FAST_KERNEL # load handler address | |
104 | jx a0 | |
105 | ||
106 | ||
107 | /* | |
108 | * Double exception vector (Exceptions with PS.EXCM == 1) | |
109 | * We get this exception when another exception occurs while were are | |
110 | * already in an exception, such as window overflow/underflow exception, | |
111 | * or 'expected' exceptions, for example memory exception when we were trying | |
112 | * to read data from an invalid address in user space. | |
113 | * | |
114 | * Note that this vector is never invoked for level-1 interrupts, because such | |
115 | * interrupts are disabled (masked) when PS.EXCM is set. | |
116 | * | |
117 | * We decode the exception and take the appropriate action. However, the | |
118 | * double exception vector is much more careful, because a lot more error | |
119 | * cases go through the double exception vector than through the user and | |
120 | * kernel exception vectors. | |
121 | * | |
122 | * Occasionally, the kernel expects a double exception to occur. This usually | |
123 | * happens when accessing user-space memory with the user's permissions | |
124 | * (l32e/s32e instructions). The kernel state, though, is not always suitable | |
125 | * for immediate transfer of control to handle_double, where "normal" exception | |
126 | * processing occurs. Also in kernel mode, TLB misses can occur if accessing | |
127 | * vmalloc memory, possibly requiring repair in a double exception handler. | |
128 | * | |
129 | * The variable at TABLE_FIXUP offset from the pointer in EXCSAVE_1 doubles as | |
130 | * a boolean variable and a pointer to a fixup routine. If the variable | |
131 | * EXC_TABLE_FIXUP is non-zero, this handler jumps to that address. A value of | |
132 | * zero indicates to use the default kernel/user exception handler. | |
133 | * There is only one exception, when the value is identical to the exc_table | |
134 | * label, the kernel is in trouble. This mechanism is used to protect critical | |
135 | * sections, mainly when the handler writes to the stack to assert the stack | |
136 | * pointer is valid. Once the fixup/default handler leaves that area, the | |
137 | * EXC_TABLE_FIXUP variable is reset to the fixup handler or zero. | |
138 | * | |
139 | * Procedures wishing to use this mechanism should set EXC_TABLE_FIXUP to the | |
140 | * nonzero address of a fixup routine before it could cause a double exception | |
141 | * and reset it before it returns. | |
142 | * | |
143 | * Some other things to take care of when a fast exception handler doesn't | |
144 | * specify a particular fixup handler but wants to use the default handlers: | |
145 | * | |
146 | * - The original stack pointer (in a1) must not be modified. The fast | |
147 | * exception handler should only use a2 as the stack pointer. | |
148 | * | |
149 | * - If the fast handler manipulates the stack pointer (in a2), it has to | |
150 | * register a valid fixup handler and cannot use the default handlers. | |
151 | * | |
152 | * - The handler can use any other generic register from a3 to a15, but it | |
153 | * must save the content of these registers to stack (PT_AREG3...PT_AREGx) | |
154 | * | |
155 | * - These registers must be saved before a double exception can occur. | |
156 | * | |
157 | * - If we ever implement handling signals while in double exceptions, the | |
158 | * number of registers a fast handler has saved (excluding a0 and a1) must | |
159 | * be written to PT_AREG1. (1 if only a3 is used, 2 for a3 and a4, etc. ) | |
160 | * | |
161 | * The fixup handlers are special handlers: | |
162 | * | |
163 | * - Fixup entry conditions differ from regular exceptions: | |
164 | * | |
165 | * a0: DEPC | |
166 | * a1: a1 | |
167 | * a2: trashed, original value in EXC_TABLE_DOUBLE_A2 | |
168 | * a3: exctable | |
169 | * depc: a0 | |
170 | * excsave_1: a3 | |
171 | * | |
172 | * - When the kernel enters the fixup handler, it still assumes it is in a | |
173 | * critical section, so EXC_TABLE_FIXUP variable is set to exc_table. | |
174 | * The fixup handler, therefore, has to re-register itself as the fixup | |
175 | * handler before it returns from the double exception. | |
176 | * | |
177 | * - Fixup handler can share the same exception frame with the fast handler. | |
178 | * The kernel stack pointer is not changed when entering the fixup handler. | |
179 | * | |
180 | * - Fixup handlers can jump to the default kernel and user exception | |
181 | * handlers. Before it jumps, though, it has to setup a exception frame | |
182 | * on stack. Because the default handler resets the register fixup handler | |
183 | * the fixup handler must make sure that the default handler returns to | |
184 | * it instead of the exception address, so it can re-register itself as | |
185 | * the fixup handler. | |
186 | * | |
187 | * In case of a critical condition where the kernel cannot recover, we jump | |
188 | * to unrecoverable_exception with the following entry conditions. | |
189 | * All registers a0...a15 are unchanged from the last exception, except: | |
190 | * | |
191 | * a0: last address before we jumped to the unrecoverable_exception. | |
192 | * excsave_1: a0 | |
193 | * | |
194 | * | |
195 | * See the handle_alloca_user and spill_registers routines for example clients. | |
196 | * | |
197 | * FIXME: Note: we currently don't allow signal handling coming from a double | |
198 | * exception, so the item markt with (*) is not required. | |
199 | */ | |
200 | ||
201 | .section .DoubleExceptionVector.text, "ax" | |
202 | .begin literal_prefix .DoubleExceptionVector | |
203 | ||
204 | ENTRY(_DoubleExceptionVector) | |
205 | ||
206 | /* Deliberately destroy excsave (don't assume it's value was valid). */ | |
207 | ||
bc5378fc | 208 | wsr a3, excsave1 # save a3 |
5a0015d6 CZ |
209 | |
210 | /* Check for kernel double exception (usually fatal). */ | |
211 | ||
bc5378fc | 212 | rsr a3, ps |
173d6681 | 213 | _bbci.l a3, PS_UM_BIT, .Lksp |
5a0015d6 CZ |
214 | |
215 | /* Check if we are currently handling a window exception. */ | |
216 | /* Note: We don't need to indicate that we enter a critical section. */ | |
217 | ||
bc5378fc | 218 | xsr a0, depc # get DEPC, save a0 |
5a0015d6 CZ |
219 | |
220 | movi a3, XCHAL_WINDOW_VECTORS_VADDR | |
221 | _bltu a0, a3, .Lfixup | |
173d6681 | 222 | addi a3, a3, WINDOW_VECTORS_SIZE |
5a0015d6 CZ |
223 | _bgeu a0, a3, .Lfixup |
224 | ||
225 | /* Window overflow/underflow exception. Get stack pointer. */ | |
226 | ||
227 | mov a3, a2 | |
228 | movi a2, exc_table | |
229 | l32i a2, a2, EXC_TABLE_KSTK | |
230 | ||
231 | /* Check for overflow/underflow exception, jump if overflow. */ | |
232 | ||
233 | _bbci.l a0, 6, .Lovfl | |
234 | ||
235 | /* a0: depc, a1: a1, a2: kstk, a3: a2, depc: a0, excsave: a3 */ | |
236 | ||
237 | /* Restart window underflow exception. | |
238 | * We return to the instruction in user space that caused the window | |
239 | * underflow exception. Therefore, we change window base to the value | |
240 | * before we entered the window underflow exception and prepare the | |
241 | * registers to return as if we were coming from a regular exception | |
242 | * by changing depc (in a0). | |
243 | * Note: We can trash the current window frame (a0...a3) and depc! | |
244 | */ | |
245 | ||
bc5378fc MF |
246 | wsr a2, depc # save stack pointer temporarily |
247 | rsr a0, ps | |
173d6681 | 248 | extui a0, a0, PS_OWB_SHIFT, 4 |
bc5378fc | 249 | wsr a0, windowbase |
5a0015d6 CZ |
250 | rsync |
251 | ||
252 | /* We are now in the previous window frame. Save registers again. */ | |
253 | ||
bc5378fc | 254 | xsr a2, depc # save a2 and get stack pointer |
5a0015d6 CZ |
255 | s32i a0, a2, PT_AREG0 |
256 | ||
bc5378fc | 257 | wsr a3, excsave1 # save a3 |
5a0015d6 CZ |
258 | movi a3, exc_table |
259 | ||
bc5378fc | 260 | rsr a0, exccause |
5a0015d6 CZ |
261 | s32i a0, a2, PT_DEPC # mark it as a regular exception |
262 | addx4 a0, a0, a3 | |
263 | l32i a0, a0, EXC_TABLE_FAST_USER | |
264 | jx a0 | |
265 | ||
266 | .Lfixup:/* Check for a fixup handler or if we were in a critical section. */ | |
267 | ||
268 | /* a0: depc, a1: a1, a2: a2, a3: trashed, depc: a0, excsave1: a3 */ | |
269 | ||
270 | movi a3, exc_table | |
271 | s32i a2, a3, EXC_TABLE_DOUBLE_SAVE # temporary variable | |
272 | ||
273 | /* Enter critical section. */ | |
274 | ||
275 | l32i a2, a3, EXC_TABLE_FIXUP | |
276 | s32i a3, a3, EXC_TABLE_FIXUP | |
277 | beq a2, a3, .Lunrecoverable_fixup # critical! | |
278 | beqz a2, .Ldflt # no handler was registered | |
279 | ||
280 | /* a0: depc, a1: a1, a2: trash, a3: exctable, depc: a0, excsave: a3 */ | |
281 | ||
282 | jx a2 | |
283 | ||
284 | .Ldflt: /* Get stack pointer. */ | |
285 | ||
286 | l32i a3, a3, EXC_TABLE_DOUBLE_SAVE | |
287 | addi a2, a3, -PT_USER_SIZE | |
288 | ||
289 | .Lovfl: /* Jump to default handlers. */ | |
290 | ||
291 | /* a0: depc, a1: a1, a2: kstk, a3: a2, depc: a0, excsave: a3 */ | |
292 | ||
bc5378fc | 293 | xsr a3, depc |
5a0015d6 CZ |
294 | s32i a0, a2, PT_DEPC |
295 | s32i a3, a2, PT_AREG0 | |
296 | ||
297 | /* a0: avail, a1: a1, a2: kstk, a3: avail, depc: a2, excsave: a3 */ | |
298 | ||
299 | movi a3, exc_table | |
bc5378fc | 300 | rsr a0, exccause |
5a0015d6 CZ |
301 | addx4 a0, a0, a3 |
302 | l32i a0, a0, EXC_TABLE_FAST_USER | |
303 | jx a0 | |
304 | ||
305 | /* | |
306 | * We only allow the ITLB miss exception if we are in kernel space. | |
307 | * All other exceptions are unexpected and thus unrecoverable! | |
308 | */ | |
309 | ||
e5083a63 | 310 | #ifdef CONFIG_MMU |
5a0015d6 CZ |
311 | .extern fast_second_level_miss_double_kernel |
312 | ||
313 | .Lksp: /* a0: a0, a1: a1, a2: a2, a3: trashed, depc: depc, excsave: a3 */ | |
314 | ||
bc5378fc | 315 | rsr a3, exccause |
173d6681 CZ |
316 | beqi a3, EXCCAUSE_ITLB_MISS, 1f |
317 | addi a3, a3, -EXCCAUSE_DTLB_MISS | |
5a0015d6 CZ |
318 | bnez a3, .Lunrecoverable |
319 | 1: movi a3, fast_second_level_miss_double_kernel | |
320 | jx a3 | |
e5083a63 JW |
321 | #else |
322 | .equ .Lksp, .Lunrecoverable | |
323 | #endif | |
5a0015d6 CZ |
324 | |
325 | /* Critical! We can't handle this situation. PANIC! */ | |
326 | ||
327 | .extern unrecoverable_exception | |
328 | ||
329 | .Lunrecoverable_fixup: | |
330 | l32i a2, a3, EXC_TABLE_DOUBLE_SAVE | |
bc5378fc | 331 | xsr a0, depc |
5a0015d6 CZ |
332 | |
333 | .Lunrecoverable: | |
bc5378fc MF |
334 | rsr a3, excsave1 |
335 | wsr a0, excsave1 | |
5a0015d6 CZ |
336 | movi a0, unrecoverable_exception |
337 | callx0 a0 | |
338 | ||
339 | .end literal_prefix | |
340 | ||
341 | ||
342 | /* | |
343 | * Debug interrupt vector | |
344 | * | |
345 | * There is not much space here, so simply jump to another handler. | |
346 | * EXCSAVE[DEBUGLEVEL] has been set to that handler. | |
347 | */ | |
348 | ||
349 | .section .DebugInterruptVector.text, "ax" | |
350 | ||
351 | ENTRY(_DebugInterruptVector) | |
bc5378fc | 352 | xsr a0, SREG_EXCSAVE + XCHAL_DEBUGLEVEL |
5a0015d6 CZ |
353 | jx a0 |
354 | ||
355 | ||
356 | ||
357 | /* Window overflow and underflow handlers. | |
358 | * The handlers must be 64 bytes apart, first starting with the underflow | |
359 | * handlers underflow-4 to underflow-12, then the overflow handlers | |
360 | * overflow-4 to overflow-12. | |
361 | * | |
362 | * Note: We rerun the underflow handlers if we hit an exception, so | |
363 | * we try to access any page that would cause a page fault early. | |
364 | */ | |
365 | ||
366 | .section .WindowVectors.text, "ax" | |
367 | ||
368 | ||
369 | /* 4-Register Window Overflow Vector (Handler) */ | |
370 | ||
371 | .align 64 | |
372 | .global _WindowOverflow4 | |
373 | _WindowOverflow4: | |
374 | s32e a0, a5, -16 | |
375 | s32e a1, a5, -12 | |
376 | s32e a2, a5, -8 | |
377 | s32e a3, a5, -4 | |
378 | rfwo | |
379 | ||
380 | ||
381 | /* 4-Register Window Underflow Vector (Handler) */ | |
382 | ||
383 | .align 64 | |
384 | .global _WindowUnderflow4 | |
385 | _WindowUnderflow4: | |
386 | l32e a0, a5, -16 | |
387 | l32e a1, a5, -12 | |
388 | l32e a2, a5, -8 | |
389 | l32e a3, a5, -4 | |
390 | rfwu | |
391 | ||
392 | ||
393 | /* 8-Register Window Overflow Vector (Handler) */ | |
394 | ||
395 | .align 64 | |
396 | .global _WindowOverflow8 | |
397 | _WindowOverflow8: | |
398 | s32e a0, a9, -16 | |
399 | l32e a0, a1, -12 | |
400 | s32e a2, a9, -8 | |
401 | s32e a1, a9, -12 | |
402 | s32e a3, a9, -4 | |
403 | s32e a4, a0, -32 | |
404 | s32e a5, a0, -28 | |
405 | s32e a6, a0, -24 | |
406 | s32e a7, a0, -20 | |
407 | rfwo | |
408 | ||
409 | /* 8-Register Window Underflow Vector (Handler) */ | |
410 | ||
411 | .align 64 | |
412 | .global _WindowUnderflow8 | |
413 | _WindowUnderflow8: | |
414 | l32e a1, a9, -12 | |
415 | l32e a0, a9, -16 | |
416 | l32e a7, a1, -12 | |
417 | l32e a2, a9, -8 | |
418 | l32e a4, a7, -32 | |
419 | l32e a3, a9, -4 | |
420 | l32e a5, a7, -28 | |
421 | l32e a6, a7, -24 | |
422 | l32e a7, a7, -20 | |
423 | rfwu | |
424 | ||
425 | ||
426 | /* 12-Register Window Overflow Vector (Handler) */ | |
427 | ||
428 | .align 64 | |
429 | .global _WindowOverflow12 | |
430 | _WindowOverflow12: | |
431 | s32e a0, a13, -16 | |
432 | l32e a0, a1, -12 | |
433 | s32e a1, a13, -12 | |
434 | s32e a2, a13, -8 | |
435 | s32e a3, a13, -4 | |
436 | s32e a4, a0, -48 | |
437 | s32e a5, a0, -44 | |
438 | s32e a6, a0, -40 | |
439 | s32e a7, a0, -36 | |
440 | s32e a8, a0, -32 | |
441 | s32e a9, a0, -28 | |
442 | s32e a10, a0, -24 | |
443 | s32e a11, a0, -20 | |
444 | rfwo | |
445 | ||
446 | /* 12-Register Window Underflow Vector (Handler) */ | |
447 | ||
448 | .align 64 | |
449 | .global _WindowUnderflow12 | |
450 | _WindowUnderflow12: | |
451 | l32e a1, a13, -12 | |
452 | l32e a0, a13, -16 | |
453 | l32e a11, a1, -12 | |
454 | l32e a2, a13, -8 | |
455 | l32e a4, a11, -48 | |
456 | l32e a8, a11, -32 | |
457 | l32e a3, a13, -4 | |
458 | l32e a5, a11, -44 | |
459 | l32e a6, a11, -40 | |
460 | l32e a7, a11, -36 | |
461 | l32e a9, a11, -28 | |
462 | l32e a10, a11, -24 | |
463 | l32e a11, a11, -20 | |
464 | rfwu | |
465 | ||
466 | .text | |
467 | ||
468 |