summaryrefslogtreecommitdiff
path: root/arch/xtensa/kernel/vectors.S
blob: eb2d7bb69ee071352ef9124efb75b7a743d27649 (plain)
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
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
/*
 * arch/xtensa/kernel/vectors.S
 *
 * This file contains all exception vectors (user, kernel, and double),
 * as well as the window vectors (overflow and underflow), and the debug
 * vector. These are the primary vectors executed by the processor if an
 * exception occurs.
 *
 * This file is subject to the terms and conditions of the GNU General
 * Public License.  See the file "COPYING" in the main directory of
 * this archive for more details.
 *
 * Copyright (C) 2005 Tensilica, Inc.
 *
 * Chris Zankel <chris@zankel.net>
 *
 */

/*
 * We use a two-level table approach. The user and kernel exception vectors
 * use a first-level dispatch table to dispatch the exception to a registered
 * fast handler or the default handler, if no fast handler was registered.
 * The default handler sets up a C-stack and dispatches the exception to a
 * registerd C handler in the second-level dispatch table.
 *
 * Fast handler entry condition:
 *
 *   a0:	trashed, original value saved on stack (PT_AREG0)
 *   a1:	a1
 *   a2:	new stack pointer, original value in depc
 *   a3:	dispatch table
 *   depc:	a2, original value saved on stack (PT_DEPC)
 *   excsave_1:	a3
 *
 * The value for PT_DEPC saved to stack also functions as a boolean to
 * indicate that the exception is either a double or a regular exception:
 *
 *   PT_DEPC	>= VALID_DOUBLE_EXCEPTION_ADDRESS: double exception
 *		<  VALID_DOUBLE_EXCEPTION_ADDRESS: regular exception
 *
 * Note:  Neither the kernel nor the user exception handler generate literals.
 *
 */

#include <linux/linkage.h>
#include <asm/ptrace.h>
#include <asm/ptrace.h>
#include <asm/current.h>
#include <asm/asm-offsets.h>
#include <asm/pgtable.h>
#include <asm/processor.h>
#include <asm/page.h>
#include <asm/thread_info.h>
#include <asm/processor.h>

#define WINDOW_VECTORS_SIZE   0x180


/*
 * User exception vector. (Exceptions with PS.UM == 1, PS.EXCM == 0)
 *
 * We get here when an exception occurred while we were in userland.
 * We switch to the kernel stack and jump to the first level handler
 * associated to the exception cause.
 *
 * Note: the saved kernel stack pointer (EXC_TABLE_KSTK) is already
 *       decremented by PT_USER_SIZE.
 */

	.section .UserExceptionVector.text, "ax"

ENTRY(_UserExceptionVector)

	xsr	a3, EXCSAVE_1		# save a3 and get dispatch table
	wsr	a2, DEPC		# save a2
	l32i	a2, a3, EXC_TABLE_KSTK	# load kernel stack to a2
	s32i	a0, a2, PT_AREG0	# save a0 to ESF
	rsr	a0, EXCCAUSE		# retrieve exception cause
	s32i	a0, a2, PT_DEPC		# mark it as a regular exception
	addx4	a0, a0, a3		# find entry in table
	l32i	a0, a0, EXC_TABLE_FAST_USER	# load handler
	jx	a0

/*
 * Kernel exception vector. (Exceptions with PS.UM == 0, PS.EXCM == 0)
 *
 * We get this exception when we were already in kernel space.
 * We decrement the current stack pointer (kernel) by PT_SIZE and
 * jump to the first-level handler associated with the exception cause.
 *
 * Note: we need to preserve space for the spill region.
 */

	.section .KernelExceptionVector.text, "ax"

ENTRY(_KernelExceptionVector)

	xsr	a3, EXCSAVE_1		# save a3, and get dispatch table
	wsr	a2, DEPC		# save a2
	addi	a2, a1, -16-PT_SIZE	# adjust stack pointer
	s32i	a0, a2, PT_AREG0	# save a0 to ESF
	rsr	a0, EXCCAUSE		# retrieve exception cause
	s32i	a0, a2, PT_DEPC		# mark it as a regular exception
	addx4	a0, a0, a3		# find entry in table
	l32i	a0, a0, EXC_TABLE_FAST_KERNEL	# load handler address
	jx	a0


/*
 * Double exception vector (Exceptions with PS.EXCM == 1)
 * We get this exception when another exception occurs while were are
 * already in an exception, such as window overflow/underflow exception,
 * or 'expected' exceptions, for example memory exception when we were trying
 * to read data from an invalid address in user space.
 *
 * Note that this vector is never invoked for level-1 interrupts, because such
 * interrupts are disabled (masked) when PS.EXCM is set.
 *
 * We decode the exception and take the appropriate action.  However, the
 * double exception vector is much more careful, because a lot more error
 * cases go through the double exception vector than through the user and
 * kernel exception vectors.
 *
 * Occasionally, the kernel expects a double exception to occur.  This usually
 * happens when accessing user-space memory with the user's permissions
 * (l32e/s32e instructions).  The kernel state, though, is not always suitable
 * for immediate transfer of control to handle_double, where "normal" exception
 * processing occurs. Also in kernel mode, TLB misses can occur if accessing
 * vmalloc memory, possibly requiring repair in a double exception handler.
 *
 * The variable at TABLE_FIXUP offset from the pointer in EXCSAVE_1 doubles as
 * a boolean variable and a pointer to a fixup routine. If the variable
 * EXC_TABLE_FIXUP is non-zero, this handler jumps to that address. A value of
 * zero indicates to use the default kernel/user exception handler.
 * There is only one exception, when the value is identical to the exc_table
 * label, the kernel is in trouble. This mechanism is used to protect critical
 * sections, mainly when the handler writes to the stack to assert the stack
 * pointer is valid. Once the fixup/default handler leaves that area, the
 * EXC_TABLE_FIXUP variable is reset to the fixup handler or zero.
 *
 * Procedures wishing to use this mechanism should set EXC_TABLE_FIXUP to the
 * nonzero address of a fixup routine before it could cause a double exception
 * and reset it before it returns.
 *
 * Some other things to take care of when a fast exception handler doesn't
 * specify a particular fixup handler but wants to use the default handlers:
 *
 *  - The original stack pointer (in a1) must not be modified. The fast
 *    exception handler should only use a2 as the stack pointer.
 *
 *  - If the fast handler manipulates the stack pointer (in a2), it has to
 *    register a valid fixup handler and cannot use the default handlers.
 *
 *  - The handler can use any other generic register from a3 to a15, but it
 *    must save the content of these registers to stack (PT_AREG3...PT_AREGx)
 *
 *  - These registers must be saved before a double exception can occur.
 *
 *  - If we ever implement handling signals while in double exceptions, the
 *    number of registers a fast handler has saved (excluding a0 and a1) must
 *    be written to  PT_AREG1. (1 if only a3 is used, 2 for a3 and a4, etc. )
 *
 * The fixup handlers are special handlers:
 *
 *  - Fixup entry conditions differ from regular exceptions:
 *
 *	a0:	   DEPC
 *	a1: 	   a1
 *	a2:	   trashed, original value in EXC_TABLE_DOUBLE_A2
 *	a3:	   exctable
 *	depc:	   a0
 *	excsave_1: a3
 *
 *  - When the kernel enters the fixup handler, it still assumes it is in a
 *    critical section, so EXC_TABLE_FIXUP variable is set to exc_table.
 *    The fixup handler, therefore, has to re-register itself as the fixup
 *    handler before it returns from the double exception.
 *
 *  - Fixup handler can share the same exception frame with the fast handler.
 *    The kernel stack pointer is not changed when entering the fixup handler.
 *
 *  - Fixup handlers can jump to the default kernel and user exception
 *    handlers. Before it jumps, though, it has to setup a exception frame
 *    on stack. Because the default handler resets the register fixup handler
 *    the fixup handler must make sure that the default handler returns to
 *    it instead of the exception address, so it can re-register itself as
 *    the fixup handler.
 *
 * In case of a critical condition where the kernel cannot recover, we jump
 * to unrecoverable_exception with the following entry conditions.
 * All registers a0...a15 are unchanged from the last exception, except:
 *
 *	a0:	   last address before we jumped to the unrecoverable_exception.
 *	excsave_1: a0
 *
 *
 * See the handle_alloca_user and spill_registers routines for example clients.
 *
 * FIXME: Note: we currently don't allow signal handling coming from a double
 *        exception, so the item markt with (*) is not required.
 */

	.section .DoubleExceptionVector.text, "ax"
	.begin literal_prefix .DoubleExceptionVector

ENTRY(_DoubleExceptionVector)

	/* Deliberately destroy excsave (don't assume it's value was valid). */

	wsr	a3, EXCSAVE_1		# save a3

	/* Check for kernel double exception (usually fatal). */

	rsr	a3, PS
	_bbci.l	a3, PS_UM_BIT, .Lksp

	/* Check if we are currently handling a window exception. */
	/* Note: We don't need to indicate that we enter a critical section. */

	xsr	a0, DEPC		# get DEPC, save a0

	movi	a3, XCHAL_WINDOW_VECTORS_VADDR
	_bltu	a0, a3, .Lfixup
	addi	a3, a3, WINDOW_VECTORS_SIZE
	_bgeu	a0, a3, .Lfixup

	/* Window overflow/underflow exception. Get stack pointer. */

	mov	a3, a2
	movi	a2, exc_table
	l32i	a2, a2, EXC_TABLE_KSTK

	/* Check for overflow/underflow exception, jump if overflow. */

	_bbci.l	a0, 6, .Lovfl

	/* a0: depc, a1: a1, a2: kstk, a3: a2, depc: a0, excsave: a3  */

	/* Restart window underflow exception.
	 * We return to the instruction in user space that caused the window
	 * underflow exception. Therefore, we change window base to the value
	 * before we entered the window underflow exception and prepare the
	 * registers to return as if we were coming from a regular exception
	 * by changing depc (in a0).
	 * Note: We can trash the current window frame (a0...a3) and depc!
	 */

	wsr	a2, DEPC		# save stack pointer temporarily
	rsr	a0, PS
	extui	a0, a0, PS_OWB_SHIFT, 4
	wsr	a0, WINDOWBASE
	rsync

	/* We are now in the previous window frame. Save registers again. */

	xsr	a2, DEPC		# save a2 and get stack pointer
	s32i	a0, a2, PT_AREG0

	wsr	a3, EXCSAVE_1		# save a3
	movi	a3, exc_table

	rsr	a0, EXCCAUSE
	s32i	a0, a2, PT_DEPC		# mark it as a regular exception
	addx4	a0, a0, a3
	l32i	a0, a0, EXC_TABLE_FAST_USER
	jx	a0

.Lfixup:/* Check for a fixup handler or if we were in a critical section. */

	/* a0: depc, a1: a1, a2: a2, a3: trashed, depc: a0, excsave1: a3 */

	movi	a3, exc_table
	s32i	a2, a3, EXC_TABLE_DOUBLE_SAVE	# temporary variable

	/* Enter critical section. */

	l32i	a2, a3, EXC_TABLE_FIXUP
	s32i	a3, a3, EXC_TABLE_FIXUP
	beq	a2, a3, .Lunrecoverable_fixup	# critical!
	beqz	a2, .Ldflt			# no handler was registered

	/* a0: depc, a1: a1, a2: trash, a3: exctable, depc: a0, excsave: a3 */

	jx	a2

.Ldflt:	/* Get stack pointer. */

	l32i	a3, a3, EXC_TABLE_DOUBLE_SAVE
	addi	a2, a3, -PT_USER_SIZE

.Lovfl:	/* Jump to default handlers. */

	/* a0: depc, a1: a1, a2: kstk, a3: a2, depc: a0, excsave: a3 */

	xsr	a3, DEPC
	s32i	a0, a2, PT_DEPC
	s32i	a3, a2, PT_AREG0

	/* a0: avail, a1: a1, a2: kstk, a3: avail, depc: a2, excsave: a3 */

	movi	a3, exc_table
	rsr	a0, EXCCAUSE
	addx4	a0, a0, a3
	l32i	a0, a0, EXC_TABLE_FAST_USER
	jx	a0

	/*
	 * We only allow the ITLB miss exception if we are in kernel space.
	 * All other exceptions are unexpected and thus unrecoverable!
	 */

	.extern fast_second_level_miss_double_kernel

.Lksp:	/* a0: a0, a1: a1, a2: a2, a3: trashed, depc: depc, excsave: a3 */

	rsr	a3, EXCCAUSE
	beqi	a3, EXCCAUSE_ITLB_MISS, 1f
	addi	a3, a3, -EXCCAUSE_DTLB_MISS
	bnez	a3, .Lunrecoverable
1:	movi	a3, fast_second_level_miss_double_kernel
	jx	a3

	/* Critical! We can't handle this situation. PANIC! */

	.extern unrecoverable_exception

.Lunrecoverable_fixup:
	l32i	a2, a3, EXC_TABLE_DOUBLE_SAVE
	xsr	a0, DEPC

.Lunrecoverable:
	rsr	a3, EXCSAVE_1
	wsr	a0, EXCSAVE_1
	movi	a0, unrecoverable_exception
	callx0	a0

	.end literal_prefix


/*
 * Debug interrupt vector
 *
 * There is not much space here, so simply jump to another handler.
 * EXCSAVE[DEBUGLEVEL] has been set to that handler.
 */

	.section .DebugInterruptVector.text, "ax"

ENTRY(_DebugInterruptVector)
	xsr	a0, EXCSAVE + XCHAL_DEBUGLEVEL
	jx	a0



/* Window overflow and underflow handlers.
 * The handlers must be 64 bytes apart, first starting with the underflow
 * handlers underflow-4 to underflow-12, then the overflow handlers
 * overflow-4 to overflow-12.
 *
 * Note: We rerun the underflow handlers if we hit an exception, so
 *	 we try to access any page that would cause a page fault early.
 */

	.section		.WindowVectors.text, "ax"


/* 4-Register Window Overflow Vector (Handler) */

	.align 64
.global _WindowOverflow4
_WindowOverflow4:
	s32e	a0, a5, -16
	s32e	a1, a5, -12
	s32e	a2, a5,  -8
	s32e	a3, a5,  -4
	rfwo


/* 4-Register Window Underflow Vector (Handler) */

	.align 64
.global _WindowUnderflow4
_WindowUnderflow4:
	l32e	a0, a5, -16
	l32e	a1, a5, -12
	l32e	a2, a5,  -8
	l32e	a3, a5,  -4
	rfwu


/* 8-Register Window Overflow Vector (Handler) */

	.align 64
.global _WindowOverflow8
_WindowOverflow8:
	s32e	a0, a9, -16
	l32e	a0, a1, -12
	s32e	a2, a9,  -8
	s32e	a1, a9, -12
	s32e	a3, a9,  -4
	s32e	a4, a0, -32
	s32e	a5, a0, -28
	s32e	a6, a0, -24
	s32e	a7, a0, -20
	rfwo

/* 8-Register Window Underflow Vector (Handler) */

	.align 64
.global _WindowUnderflow8
_WindowUnderflow8:
	l32e	a1, a9, -12
	l32e	a0, a9, -16
	l32e	a7, a1, -12
	l32e	a2, a9,  -8
	l32e	a4, a7, -32
	l32e	a3, a9,  -4
	l32e	a5, a7, -28
	l32e	a6, a7, -24
	l32e	a7, a7, -20
	rfwu


/* 12-Register Window Overflow Vector (Handler) */

	.align 64
.global _WindowOverflow12
_WindowOverflow12:
	s32e	a0,  a13, -16
	l32e	a0,  a1,  -12
	s32e	a1,  a13, -12
	s32e	a2,  a13,  -8
	s32e	a3,  a13,  -4
	s32e	a4,  a0,  -48
	s32e	a5,  a0,  -44
	s32e	a6,  a0,  -40
	s32e	a7,  a0,  -36
	s32e	a8,  a0,  -32
	s32e	a9,  a0,  -28
	s32e	a10, a0,  -24
	s32e	a11, a0,  -20
	rfwo

/* 12-Register Window Underflow Vector (Handler) */

	.align 64
.global _WindowUnderflow12
_WindowUnderflow12:
	l32e	a1,  a13, -12
	l32e	a0,  a13, -16
	l32e	a11, a1,  -12
	l32e	a2,  a13,  -8
	l32e	a4,  a11, -48
	l32e	a8,  a11, -32
	l32e	a3,  a13,  -4
	l32e	a5,  a11, -44
	l32e	a6,  a11, -40
	l32e	a7,  a11, -36
	l32e	a9,  a11, -28
	l32e	a10, a11, -24
	l32e	a11, a11, -20
	rfwu

	.text