Free Electrons

Embedded Linux Experts

  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
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
/*
 * arch/arm/kernel/unwind.c
 *
 * Copyright (C) 2008 ARM Limited
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 *
 *
 * Stack unwinding support for ARM
 *
 * An ARM EABI version of gcc is required to generate the unwind
 * tables. For information about the structure of the unwind tables,
 * see "Exception Handling ABI for the ARM Architecture" at:
 *
 * http://infocenter.arm.com/help/topic/com.arm.doc.subset.swdev.abi/index.html
 */

#ifndef __CHECKER__
#if !defined (__ARM_EABI__)
#warning Your compiler does not have EABI support.
#warning    ARM unwind is known to compile only with EABI compilers.
#warning    Change compiler or disable ARM_UNWIND option.
#elif (__GNUC__ == 4 && __GNUC_MINOR__ <= 2) && !defined(__clang__)
#warning Your compiler is too buggy; it is known to not compile ARM unwind support.
#warning    Change compiler or disable ARM_UNWIND option.
#endif
#endif /* __CHECKER__ */

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/export.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/list.h>

#include <asm/stacktrace.h>
#include <asm/traps.h>
#include <asm/unwind.h>

/* Dummy functions to avoid linker complaints */
void __aeabi_unwind_cpp_pr0(void)
{
};
EXPORT_SYMBOL(__aeabi_unwind_cpp_pr0);

void __aeabi_unwind_cpp_pr1(void)
{
};
EXPORT_SYMBOL(__aeabi_unwind_cpp_pr1);

void __aeabi_unwind_cpp_pr2(void)
{
};
EXPORT_SYMBOL(__aeabi_unwind_cpp_pr2);

struct unwind_ctrl_block {
	unsigned long vrs[16];		/* virtual register set */
	const unsigned long *insn;	/* pointer to the current instructions word */
	unsigned long sp_high;		/* highest value of sp allowed */
	/*
	 * 1 : check for stack overflow for each register pop.
	 * 0 : save overhead if there is plenty of stack remaining.
	 */
	int check_each_pop;
	int entries;			/* number of entries left to interpret */
	int byte;			/* current byte number in the instructions word */
};

enum regs {
#ifdef CONFIG_THUMB2_KERNEL
	FP = 7,
#else
	FP = 11,
#endif
	SP = 13,
	LR = 14,
	PC = 15
};

extern const struct unwind_idx __start_unwind_idx[];
static const struct unwind_idx *__origin_unwind_idx;
extern const struct unwind_idx __stop_unwind_idx[];

static DEFINE_SPINLOCK(unwind_lock);
static LIST_HEAD(unwind_tables);

/* Convert a prel31 symbol to an absolute address */
#define prel31_to_addr(ptr)				\
({							\
	/* sign-extend to 32 bits */			\
	long offset = (((long)*(ptr)) << 1) >> 1;	\
	(unsigned long)(ptr) + offset;			\
})

/*
 * Binary search in the unwind index. The entries are
 * guaranteed to be sorted in ascending order by the linker.
 *
 * start = first entry
 * origin = first entry with positive offset (or stop if there is no such entry)
 * stop - 1 = last entry
 */
static const struct unwind_idx *search_index(unsigned long addr,
				       const struct unwind_idx *start,
				       const struct unwind_idx *origin,
				       const struct unwind_idx *stop)
{
	unsigned long addr_prel31;

	pr_debug("%s(%08lx, %p, %p, %p)\n",
			__func__, addr, start, origin, stop);

	/*
	 * only search in the section with the matching sign. This way the
	 * prel31 numbers can be compared as unsigned longs.
	 */
	if (addr < (unsigned long)start)
		/* negative offsets: [start; origin) */
		stop = origin;
	else
		/* positive offsets: [origin; stop) */
		start = origin;

	/* prel31 for address relavive to start */
	addr_prel31 = (addr - (unsigned long)start) & 0x7fffffff;

	while (start < stop - 1) {
		const struct unwind_idx *mid = start + ((stop - start) >> 1);

		/*
		 * As addr_prel31 is relative to start an offset is needed to
		 * make it relative to mid.
		 */
		if (addr_prel31 - ((unsigned long)mid - (unsigned long)start) <
				mid->addr_offset)
			stop = mid;
		else {
			/* keep addr_prel31 relative to start */
			addr_prel31 -= ((unsigned long)mid -
					(unsigned long)start);
			start = mid;
		}
	}

	if (likely(start->addr_offset <= addr_prel31))
		return start;
	else {
		pr_warn("unwind: Unknown symbol address %08lx\n", addr);
		return NULL;
	}
}

static const struct unwind_idx *unwind_find_origin(
		const struct unwind_idx *start, const struct unwind_idx *stop)
{
	pr_debug("%s(%p, %p)\n", __func__, start, stop);
	while (start < stop) {
		const struct unwind_idx *mid = start + ((stop - start) >> 1);

		if (mid->addr_offset >= 0x40000000)
			/* negative offset */
			start = mid + 1;
		else
			/* positive offset */
			stop = mid;
	}
	pr_debug("%s -> %p\n", __func__, stop);
	return stop;
}

static const struct unwind_idx *unwind_find_idx(unsigned long addr)
{
	const struct unwind_idx *idx = NULL;
	unsigned long flags;

	pr_debug("%s(%08lx)\n", __func__, addr);

	if (core_kernel_text(addr)) {
		if (unlikely(!__origin_unwind_idx))
			__origin_unwind_idx =
				unwind_find_origin(__start_unwind_idx,
						__stop_unwind_idx);

		/* main unwind table */
		idx = search_index(addr, __start_unwind_idx,
				   __origin_unwind_idx,
				   __stop_unwind_idx);
	} else {
		/* module unwind tables */
		struct unwind_table *table;

		spin_lock_irqsave(&unwind_lock, flags);
		list_for_each_entry(table, &unwind_tables, list) {
			if (addr >= table->begin_addr &&
			    addr < table->end_addr) {
				idx = search_index(addr, table->start,
						   table->origin,
						   table->stop);
				/* Move-to-front to exploit common traces */
				list_move(&table->list, &unwind_tables);
				break;
			}
		}
		spin_unlock_irqrestore(&unwind_lock, flags);
	}

	pr_debug("%s: idx = %p\n", __func__, idx);
	return idx;
}

static unsigned long unwind_get_byte(struct unwind_ctrl_block *ctrl)
{
	unsigned long ret;

	if (ctrl->entries <= 0) {
		pr_warn("unwind: Corrupt unwind table\n");
		return 0;
	}

	ret = (*ctrl->insn >> (ctrl->byte * 8)) & 0xff;

	if (ctrl->byte == 0) {
		ctrl->insn++;
		ctrl->entries--;
		ctrl->byte = 3;
	} else
		ctrl->byte--;

	return ret;
}

/* Before poping a register check whether it is feasible or not */
static int unwind_pop_register(struct unwind_ctrl_block *ctrl,
				unsigned long **vsp, unsigned int reg)
{
	if (unlikely(ctrl->check_each_pop))
		if (*vsp >= (unsigned long *)ctrl->sp_high)
			return -URC_FAILURE;

	ctrl->vrs[reg] = *(*vsp)++;
	return URC_OK;
}

/* Helper functions to execute the instructions */
static int unwind_exec_pop_subset_r4_to_r13(struct unwind_ctrl_block *ctrl,
						unsigned long mask)
{
	unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
	int load_sp, reg = 4;

	load_sp = mask & (1 << (13 - 4));
	while (mask) {
		if (mask & 1)
			if (unwind_pop_register(ctrl, &vsp, reg))
				return -URC_FAILURE;
		mask >>= 1;
		reg++;
	}
	if (!load_sp)
		ctrl->vrs[SP] = (unsigned long)vsp;

	return URC_OK;
}

static int unwind_exec_pop_r4_to_rN(struct unwind_ctrl_block *ctrl,
					unsigned long insn)
{
	unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
	int reg;

	/* pop R4-R[4+bbb] */
	for (reg = 4; reg <= 4 + (insn & 7); reg++)
		if (unwind_pop_register(ctrl, &vsp, reg))
				return -URC_FAILURE;

	if (insn & 0x8)
		if (unwind_pop_register(ctrl, &vsp, 14))
				return -URC_FAILURE;

	ctrl->vrs[SP] = (unsigned long)vsp;

	return URC_OK;
}

static int unwind_exec_pop_subset_r0_to_r3(struct unwind_ctrl_block *ctrl,
						unsigned long mask)
{
	unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
	int reg = 0;

	/* pop R0-R3 according to mask */
	while (mask) {
		if (mask & 1)
			if (unwind_pop_register(ctrl, &vsp, reg))
				return -URC_FAILURE;
		mask >>= 1;
		reg++;
	}
	ctrl->vrs[SP] = (unsigned long)vsp;

	return URC_OK;
}

/*
 * Execute the current unwind instruction.
 */
static int unwind_exec_insn(struct unwind_ctrl_block *ctrl)
{
	unsigned long insn = unwind_get_byte(ctrl);
	int ret = URC_OK;

	pr_debug("%s: insn = %08lx\n", __func__, insn);

	if ((insn & 0xc0) == 0x00)
		ctrl->vrs[SP] += ((insn & 0x3f) << 2) + 4;
	else if ((insn & 0xc0) == 0x40)
		ctrl->vrs[SP] -= ((insn & 0x3f) << 2) + 4;
	else if ((insn & 0xf0) == 0x80) {
		unsigned long mask;

		insn = (insn << 8) | unwind_get_byte(ctrl);
		mask = insn & 0x0fff;
		if (mask == 0) {
			pr_warn("unwind: 'Refuse to unwind' instruction %04lx\n",
				insn);
			return -URC_FAILURE;
		}

		ret = unwind_exec_pop_subset_r4_to_r13(ctrl, mask);
		if (ret)
			goto error;
	} else if ((insn & 0xf0) == 0x90 &&
		   (insn & 0x0d) != 0x0d)
		ctrl->vrs[SP] = ctrl->vrs[insn & 0x0f];
	else if ((insn & 0xf0) == 0xa0) {
		ret = unwind_exec_pop_r4_to_rN(ctrl, insn);
		if (ret)
			goto error;
	} else if (insn == 0xb0) {
		if (ctrl->vrs[PC] == 0)
			ctrl->vrs[PC] = ctrl->vrs[LR];
		/* no further processing */
		ctrl->entries = 0;
	} else if (insn == 0xb1) {
		unsigned long mask = unwind_get_byte(ctrl);

		if (mask == 0 || mask & 0xf0) {
			pr_warn("unwind: Spare encoding %04lx\n",
				(insn << 8) | mask);
			return -URC_FAILURE;
		}

		ret = unwind_exec_pop_subset_r0_to_r3(ctrl, mask);
		if (ret)
			goto error;
	} else if (insn == 0xb2) {
		unsigned long uleb128 = unwind_get_byte(ctrl);

		ctrl->vrs[SP] += 0x204 + (uleb128 << 2);
	} else {
		pr_warn("unwind: Unhandled instruction %02lx\n", insn);
		return -URC_FAILURE;
	}

	pr_debug("%s: fp = %08lx sp = %08lx lr = %08lx pc = %08lx\n", __func__,
		 ctrl->vrs[FP], ctrl->vrs[SP], ctrl->vrs[LR], ctrl->vrs[PC]);

error:
	return ret;
}

/*
 * Unwind a single frame starting with *sp for the symbol at *pc. It
 * updates the *pc and *sp with the new values.
 */
int unwind_frame(struct stackframe *frame)
{
	unsigned long low;
	const struct unwind_idx *idx;
	struct unwind_ctrl_block ctrl;

	/* store the highest address on the stack to avoid crossing it*/
	low = frame->sp;
	ctrl.sp_high = ALIGN(low, THREAD_SIZE);

	pr_debug("%s(pc = %08lx lr = %08lx sp = %08lx)\n", __func__,
		 frame->pc, frame->lr, frame->sp);

	if (!kernel_text_address(frame->pc))
		return -URC_FAILURE;

	idx = unwind_find_idx(frame->pc);
	if (!idx) {
		pr_warn("unwind: Index not found %08lx\n", frame->pc);
		return -URC_FAILURE;
	}

	ctrl.vrs[FP] = frame->fp;
	ctrl.vrs[SP] = frame->sp;
	ctrl.vrs[LR] = frame->lr;
	ctrl.vrs[PC] = 0;

	if (idx->insn == 1)
		/* can't unwind */
		return -URC_FAILURE;
	else if ((idx->insn & 0x80000000) == 0)
		/* prel31 to the unwind table */
		ctrl.insn = (unsigned long *)prel31_to_addr(&idx->insn);
	else if ((idx->insn & 0xff000000) == 0x80000000)
		/* only personality routine 0 supported in the index */
		ctrl.insn = &idx->insn;
	else {
		pr_warn("unwind: Unsupported personality routine %08lx in the index at %p\n",
			idx->insn, idx);
		return -URC_FAILURE;
	}

	/* check the personality routine */
	if ((*ctrl.insn & 0xff000000) == 0x80000000) {
		ctrl.byte = 2;
		ctrl.entries = 1;
	} else if ((*ctrl.insn & 0xff000000) == 0x81000000) {
		ctrl.byte = 1;
		ctrl.entries = 1 + ((*ctrl.insn & 0x00ff0000) >> 16);
	} else {
		pr_warn("unwind: Unsupported personality routine %08lx at %p\n",
			*ctrl.insn, ctrl.insn);
		return -URC_FAILURE;
	}

	ctrl.check_each_pop = 0;

	while (ctrl.entries > 0) {
		int urc;
		if ((ctrl.sp_high - ctrl.vrs[SP]) < sizeof(ctrl.vrs))
			ctrl.check_each_pop = 1;
		urc = unwind_exec_insn(&ctrl);
		if (urc < 0)
			return urc;
		if (ctrl.vrs[SP] < low || ctrl.vrs[SP] >= ctrl.sp_high)
			return -URC_FAILURE;
	}

	if (ctrl.vrs[PC] == 0)
		ctrl.vrs[PC] = ctrl.vrs[LR];

	/* check for infinite loop */
	if (frame->pc == ctrl.vrs[PC])
		return -URC_FAILURE;

	frame->fp = ctrl.vrs[FP];
	frame->sp = ctrl.vrs[SP];
	frame->lr = ctrl.vrs[LR];
	frame->pc = ctrl.vrs[PC];

	return URC_OK;
}

void unwind_backtrace(struct pt_regs *regs, struct task_struct *tsk)
{
	struct stackframe frame;

	pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);

	if (!tsk)
		tsk = current;

	if (regs) {
		arm_get_current_stackframe(regs, &frame);
		/* PC might be corrupted, use LR in that case. */
		if (!kernel_text_address(regs->ARM_pc))
			frame.pc = regs->ARM_lr;
	} else if (tsk == current) {
		frame.fp = (unsigned long)__builtin_frame_address(0);
		frame.sp = current_stack_pointer;
		frame.lr = (unsigned long)__builtin_return_address(0);
		frame.pc = (unsigned long)unwind_backtrace;
	} else {
		/* task blocked in __switch_to */
		frame.fp = thread_saved_fp(tsk);
		frame.sp = thread_saved_sp(tsk);
		/*
		 * The function calling __switch_to cannot be a leaf function
		 * so LR is recovered from the stack.
		 */
		frame.lr = 0;
		frame.pc = thread_saved_pc(tsk);
	}

	while (1) {
		int urc;
		unsigned long where = frame.pc;

		urc = unwind_frame(&frame);
		if (urc < 0)
			break;
		dump_backtrace_entry(where, frame.pc, frame.sp - 4);
	}
}

struct unwind_table *unwind_table_add(unsigned long start, unsigned long size,
				      unsigned long text_addr,
				      unsigned long text_size)
{
	unsigned long flags;
	struct unwind_table *tab = kmalloc(sizeof(*tab), GFP_KERNEL);

	pr_debug("%s(%08lx, %08lx, %08lx, %08lx)\n", __func__, start, size,
		 text_addr, text_size);

	if (!tab)
		return tab;

	tab->start = (const struct unwind_idx *)start;
	tab->stop = (const struct unwind_idx *)(start + size);
	tab->origin = unwind_find_origin(tab->start, tab->stop);
	tab->begin_addr = text_addr;
	tab->end_addr = text_addr + text_size;

	spin_lock_irqsave(&unwind_lock, flags);
	list_add_tail(&tab->list, &unwind_tables);
	spin_unlock_irqrestore(&unwind_lock, flags);

	return tab;
}

void unwind_table_del(struct unwind_table *tab)
{
	unsigned long flags;

	if (!tab)
		return;

	spin_lock_irqsave(&unwind_lock, flags);
	list_del(&tab->list);
	spin_unlock_irqrestore(&unwind_lock, flags);

	kfree(tab);
}