summaryrefslogtreecommitdiffstats
path: root/arch/sh/kernel/dwarf.c
blob: 1a2526676a8729b08b87c3955ed7ba007c5e531c (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
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
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
/*
 * Copyright (C) 2009 Matt Fleming <matt@console-pimps.org>
 *
 * 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.
 *
 * This is an implementation of a DWARF unwinder. Its main purpose is
 * for generating stacktrace information. Based on the DWARF 3
 * specification from http://www.dwarfstd.org.
 *
 * TODO:
 *	- DWARF64 doesn't work.
 *	- Registers with DWARF_VAL_OFFSET rules aren't handled properly.
 */

/* #define DEBUG */
#include <linux/kernel.h>
#include <linux/io.h>
#include <linux/list.h>
#include <linux/mempool.h>
#include <linux/mm.h>
#include <linux/elf.h>
#include <linux/ftrace.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <asm/dwarf.h>
#include <asm/unwinder.h>
#include <asm/sections.h>
#include <asm/unaligned.h>
#include <asm/stacktrace.h>

/* Reserve enough memory for two stack frames */
#define DWARF_FRAME_MIN_REQ	2
/* ... with 4 registers per frame. */
#define DWARF_REG_MIN_REQ	(DWARF_FRAME_MIN_REQ * 4)

static struct kmem_cache *dwarf_frame_cachep;
static mempool_t *dwarf_frame_pool;

static struct kmem_cache *dwarf_reg_cachep;
static mempool_t *dwarf_reg_pool;

static struct rb_root cie_root;
static DEFINE_SPINLOCK(dwarf_cie_lock);

static struct rb_root fde_root;
static DEFINE_SPINLOCK(dwarf_fde_lock);

static struct dwarf_cie *cached_cie;

static unsigned int dwarf_unwinder_ready;

/**
 *	dwarf_frame_alloc_reg - allocate memory for a DWARF register
 *	@frame: the DWARF frame whose list of registers we insert on
 *	@reg_num: the register number
 *
 *	Allocate space for, and initialise, a dwarf reg from
 *	dwarf_reg_pool and insert it onto the (unsorted) linked-list of
 *	dwarf registers for @frame.
 *
 *	Return the initialised DWARF reg.
 */
static struct dwarf_reg *dwarf_frame_alloc_reg(struct dwarf_frame *frame,
					       unsigned int reg_num)
{
	struct dwarf_reg *reg;

	reg = mempool_alloc(dwarf_reg_pool, GFP_ATOMIC);
	if (!reg) {
		printk(KERN_WARNING "Unable to allocate a DWARF register\n");
		/*
		 * Let's just bomb hard here, we have no way to
		 * gracefully recover.
		 */
		UNWINDER_BUG();
	}

	reg->number = reg_num;
	reg->addr = 0;
	reg->flags = 0;

	list_add(&reg->link, &frame->reg_list);

	return reg;
}

static void dwarf_frame_free_regs(struct dwarf_frame *frame)
{
	struct dwarf_reg *reg, *n;

	list_for_each_entry_safe(reg, n, &frame->reg_list, link) {
		list_del(&reg->link);
		mempool_free(reg, dwarf_reg_pool);
	}
}

/**
 *	dwarf_frame_reg - return a DWARF register
 *	@frame: the DWARF frame to search in for @reg_num
 *	@reg_num: the register number to search for
 *
 *	Lookup and return the dwarf reg @reg_num for this frame. Return
 *	NULL if @reg_num is an register invalid number.
 */
static struct dwarf_reg *dwarf_frame_reg(struct dwarf_frame *frame,
					 unsigned int reg_num)
{
	struct dwarf_reg *reg;

	list_for_each_entry(reg, &frame->reg_list, link) {
		if (reg->number == reg_num)
			return reg;
	}

	return NULL;
}

/**
 *	dwarf_read_addr - read dwarf data
 *	@src: source address of data
 *	@dst: destination address to store the data to
 *
 *	Read 'n' bytes from @src, where 'n' is the size of an address on
 *	the native machine. We return the number of bytes read, which
 *	should always be 'n'. We also have to be careful when reading
 *	from @src and writing to @dst, because they can be arbitrarily
 *	aligned. Return 'n' - the number of bytes read.
 */
static inline int dwarf_read_addr(unsigned long *src, unsigned long *dst)
{
	u32 val = get_unaligned(src);
	put_unaligned(val, dst);
	return sizeof(unsigned long *);
}

/**
 *	dwarf_read_uleb128 - read unsigned LEB128 data
 *	@addr: the address where the ULEB128 data is stored
 *	@ret: address to store the result
 *
 *	Decode an unsigned LEB128 encoded datum. The algorithm is taken
 *	from Appendix C of the DWARF 3 spec. For information on the
 *	encodings refer to section "7.6 - Variable Length Data". Return
 *	the number of bytes read.
 */
static inline unsigned long dwarf_read_uleb128(char *addr, unsigned int *ret)
{
	unsigned int result;
	unsigned char byte;
	int shift, count;

	result = 0;
	shift = 0;
	count = 0;

	while (1) {
		byte = __raw_readb(addr);
		addr++;
		count++;

		result |= (byte & 0x7f) << shift;
		shift += 7;

		if (!(byte & 0x80))
			break;
	}

	*ret = result;

	return count;
}

/**
 *	dwarf_read_leb128 - read signed LEB128 data
 *	@addr: the address of the LEB128 encoded data
 *	@ret: address to store the result
 *
 *	Decode signed LEB128 data. The algorithm is taken from Appendix
 *	C of the DWARF 3 spec. Return the number of bytes read.
 */
static inline unsigned long dwarf_read_leb128(char *addr, int *ret)
{
	unsigned char byte;
	int result, shift;
	int num_bits;
	int count;

	result = 0;
	shift = 0;
	count = 0;

	while (1) {
		byte = __raw_readb(addr);
		addr++;
		result |= (byte & 0x7f) << shift;
		shift += 7;
		count++;

		if (!(byte & 0x80))
			break;
	}

	/* The number of bits in a signed integer. */
	num_bits = 8 * sizeof(result);

	if ((shift < num_bits) && (byte & 0x40))
		result |= (-1 << shift);

	*ret = result;

	return count;
}

/**
 *	dwarf_read_encoded_value - return the decoded value at @addr
 *	@addr: the address of the encoded value
 *	@val: where to write the decoded value
 *	@encoding: the encoding with which we can decode @addr
 *
 *	GCC emits encoded address in the .eh_frame FDE entries. Decode
 *	the value at @addr using @encoding. The decoded value is written
 *	to @val and the number of bytes read is returned.
 */
static int dwarf_read_encoded_value(char *addr, unsigned long *val,
				    char encoding)
{
	unsigned long decoded_addr = 0;
	int count = 0;

	switch (encoding & 0x70) {
	case DW_EH_PE_absptr:
		break;
	case DW_EH_PE_pcrel:
		decoded_addr = (unsigned long)addr;
		break;
	default:
		pr_debug("encoding=0x%x\n", (encoding & 0x70));
		UNWINDER_BUG();
	}

	if ((encoding & 0x07) == 0x00)
		encoding |= DW_EH_PE_udata4;

	switch (encoding & 0x0f) {
	case DW_EH_PE_sdata4:
	case DW_EH_PE_udata4:
		count += 4;
		decoded_addr += get_unaligned((u32 *)addr);
		__raw_writel(decoded_addr, val);
		break;
	default:
		pr_debug("encoding=0x%x\n", encoding);
		UNWINDER_BUG();
	}

	return count;
}

/**
 *	dwarf_entry_len - return the length of an FDE or CIE
 *	@addr: the address of the entry
 *	@len: the length of the entry
 *
 *	Read the initial_length field of the entry and store the size of
 *	the entry in @len. We return the number of bytes read. Return a
 *	count of 0 on error.
 */
static inline int dwarf_entry_len(char *addr, unsigned long *len)
{
	u32 initial_len;
	int count;

	initial_len = get_unaligned((u32 *)addr);
	count = 4;

	/*
	 * An initial length field value in the range DW_LEN_EXT_LO -
	 * DW_LEN_EXT_HI indicates an extension, and should not be
	 * interpreted as a length. The only extension that we currently
	 * understand is the use of DWARF64 addresses.
	 */
	if (initial_len >= DW_EXT_LO && initial_len <= DW_EXT_HI) {
		/*
		 * The 64-bit length field immediately follows the
		 * compulsory 32-bit length field.
		 */
		if (initial_len == DW_EXT_DWARF64) {
			*len = get_unaligned((u64 *)addr + 4);
			count = 12;
		} else {
			printk(KERN_WARNING "Unknown DWARF extension\n");
			count = 0;
		}
	} else
		*len = initial_len;

	return count;
}

/**
 *	dwarf_lookup_cie - locate the cie
 *	@cie_ptr: pointer to help with lookup
 */
static struct dwarf_cie *dwarf_lookup_cie(unsigned long cie_ptr)
{
	struct rb_node **rb_node = &cie_root.rb_node;
	struct dwarf_cie *cie = NULL;
	unsigned long flags;

	spin_lock_irqsave(&dwarf_cie_lock, flags);

	/*
	 * We've cached the last CIE we looked up because chances are
	 * that the FDE wants this CIE.
	 */
	if (cached_cie && cached_cie->cie_pointer == cie_ptr) {
		cie = cached_cie;
		goto out;
	}

	while (*rb_node) {
		struct dwarf_cie *cie_tmp;

		cie_tmp = rb_entry(*rb_node, struct dwarf_cie, node);
		BUG_ON(!cie_tmp);

		if (cie_ptr == cie_tmp->cie_pointer) {
			cie = cie_tmp;
			cached_cie = cie_tmp;
			goto out;
		} else {
			if (cie_ptr < cie_tmp->cie_pointer)
				rb_node = &(*rb_node)->rb_left;
			else
				rb_node = &(*rb_node)->rb_right;
		}
	}

out:
	spin_unlock_irqrestore(&dwarf_cie_lock, flags);
	return cie;
}

/**
 *	dwarf_lookup_fde - locate the FDE that covers pc
 *	@pc: the program counter
 */
struct dwarf_fde *dwarf_lookup_fde(unsigned long pc)
{
	struct rb_node **rb_node = &fde_root.rb_node;
	struct dwarf_fde *fde = NULL;
	unsigned long flags;

	spin_lock_irqsave(&dwarf_fde_lock, flags);

	while (*rb_node) {
		struct dwarf_fde *fde_tmp;
		unsigned long tmp_start, tmp_end;

		fde_tmp = rb_entry(*rb_node, struct dwarf_fde, node);
		BUG_ON(!fde_tmp);

		tmp_start = fde_tmp->initial_location;
		tmp_end = fde_tmp->initial_location + fde_tmp->address_range;

		if (pc < tmp_start) {
			rb_node = &(*rb_node)->rb_left;
		} else {
			if (pc < tmp_end) {
				fde = fde_tmp;
				goto out;
			} else
				rb_node = &(*rb_node)->rb_right;
		}
	}

out:
	spin_unlock_irqrestore(&dwarf_fde_lock, flags);

	return fde;
}

/**
 *	dwarf_cfa_execute_insns - execute instructions to calculate a CFA
 *	@insn_start: address of the first instruction
 *	@insn_end: address of the last instruction
 *	@cie: the CIE for this function
 *	@fde: the FDE for this function
 *	@frame: the instructions calculate the CFA for this frame
 *	@pc: the program counter of the address we're interested in
 *
 *	Execute the Call Frame instruction sequence starting at
 *	@insn_start and ending at @insn_end. The instructions describe
 *	how to calculate the Canonical Frame Address of a stackframe.
 *	Store the results in @frame.
 */
static int dwarf_cfa_execute_insns(unsigned char *insn_start,
				   unsigned char *insn_end,
				   struct dwarf_cie *cie,
				   struct dwarf_fde *fde,
				   struct dwarf_frame *frame,
				   unsigned long pc)
{
	unsigned char insn;
	unsigned char *current_insn;
	unsigned int count, delta, reg, expr_len, offset;
	struct dwarf_reg *regp;

	current_insn = insn_start;

	while (current_insn < insn_end && frame->pc <= pc) {
		insn = __raw_readb(current_insn++);

		/*
		 * Firstly, handle the opcodes that embed their operands
		 * in the instructions.
		 */
		switch (DW_CFA_opcode(insn)) {
		case DW_CFA_advance_loc:
			delta = DW_CFA_operand(insn);
			delta *= cie->code_alignment_factor;
			frame->pc += delta;
			continue;
			/* NOTREACHED */
		case DW_CFA_offset:
			reg = DW_CFA_operand(insn);
			count = dwarf_read_uleb128(current_insn, &offset);
			current_insn += count;
			offset *= cie->data_alignment_factor;
			regp = dwarf_frame_alloc_reg(frame, reg);
			regp->addr = offset;
			regp->flags |= DWARF_REG_OFFSET;
			continue;
			/* NOTREACHED */
		case DW_CFA_restore:
			reg = DW_CFA_operand(insn);
			continue;
			/* NOTREACHED */
		}

		/*
		 * Secondly, handle the opcodes that don't embed their
		 * operands in the instruction.
		 */
		switch (insn) {
		case DW_CFA_nop:
			continue;
		case DW_CFA_advance_loc1:
			delta = *current_insn++;
			frame->pc += delta * cie->code_alignment_factor;
			break;
		case DW_CFA_advance_loc2:
			delta = get_unaligned((u16 *)current_insn);
			current_insn += 2;
			frame->pc += delta * cie->code_alignment_factor;
			break;
		case DW_CFA_advance_loc4:
			delta = get_unaligned((u32 *)current_insn);
			current_insn += 4;
			frame->pc += delta * cie->code_alignment_factor;
			break;
		case DW_CFA_offset_extended:
			count = dwarf_read_uleb128(current_insn, &reg);
			current_insn += count;
			count = dwarf_read_uleb128(current_insn, &offset);
			current_insn += count;
			offset *= cie->data_alignment_factor;
			break;
		case DW_CFA_restore_extended:
			count = dwarf_read_uleb128(current_insn, &reg);
			current_insn += count;
			break;
		case DW_CFA_undefined:
			count = dwarf_read_uleb128(current_insn, &reg);
			current_insn += count;
			regp = dwarf_frame_alloc_reg(frame, reg);
			regp->flags |= DWARF_UNDEFINED;
			break;
		case DW_CFA_def_cfa:
			count = dwarf_read_uleb128(current_insn,
						   &frame->cfa_register);
			current_insn += count;
			count = dwarf_read_uleb128(current_insn,
						   &frame->cfa_offset);
			current_insn += count;

			frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
			break;
		case DW_CFA_def_cfa_register:
			count = dwarf_read_uleb128(current_insn,
						   &frame->cfa_register);
			current_insn += count;
			frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
			break;
		case DW_CFA_def_cfa_offset:
			count = dwarf_read_uleb128(current_insn, &offset);
			current_insn += count;
			frame->cfa_offset = offset;
			break;
		case DW_CFA_def_cfa_expression:
			count = dwarf_read_uleb128(current_insn, &expr_len);
			current_insn += count;

			frame->cfa_expr = current_insn;
			frame->cfa_expr_len = expr_len;
			current_insn += expr_len;

			frame->flags |= DWARF_FRAME_CFA_REG_EXP;
			break;
		case DW_CFA_offset_extended_sf:
			count = dwarf_read_uleb128(current_insn, &reg);
			current_insn += count;
			count = dwarf_read_leb128(current_insn, &offset);
			current_insn += count;
			offset *= cie->data_alignment_factor;
			regp = dwarf_frame_alloc_reg(frame, reg);
			regp->flags |= DWARF_REG_OFFSET;
			regp->addr = offset;
			break;
		case DW_CFA_val_offset:
			count = dwarf_read_uleb128(current_insn, &reg);
			current_insn += count;
			count = dwarf_read_leb128(current_insn, &offset);
			offset *= cie->data_alignment_factor;
			regp = dwarf_frame_alloc_reg(frame, reg);
			regp->flags |= DWARF_VAL_OFFSET;
			regp->addr = offset;
			break;
		case DW_CFA_GNU_args_size:
			count = dwarf_read_uleb128(current_insn, &offset);
			current_insn += count;
			break;
		case DW_CFA_GNU_negative_offset_extended:
			count = dwarf_read_uleb128(current_insn, &reg);
			current_insn += count;
			count = dwarf_read_uleb128(current_insn, &offset);
			offset *= cie->data_alignment_factor;

			regp = dwarf_frame_alloc_reg(frame, reg);
			regp->flags |= DWARF_REG_OFFSET;
			regp->addr = -offset;
			break;
		default:
			pr_debug("unhandled DWARF instruction 0x%x\n", insn);
			UNWINDER_BUG();
			break;
		}
	}

	return 0;
}

/**
 *	dwarf_free_frame - free the memory allocated for @frame
 *	@frame: the frame to free
 */
void dwarf_free_frame(struct dwarf_frame *frame)
{
	dwarf_frame_free_regs(frame);
	mempool_free(frame, dwarf_frame_pool);
}

extern void ret_from_irq(void);

/**
 *	dwarf_unwind_stack - unwind the stack
 *
 *	@pc: address of the function to unwind
 *	@prev: struct dwarf_frame of the previous stackframe on the callstack
 *
 *	Return a struct dwarf_frame representing the most recent frame
 *	on the callstack. Each of the lower (older) stack frames are
 *	linked via the "prev" member.
 */
struct dwarf_frame *dwarf_unwind_stack(unsigned long pc,
				       struct dwarf_frame *prev)
{
	struct dwarf_frame *frame;
	struct dwarf_cie *cie;
	struct dwarf_fde *fde;
	struct dwarf_reg *reg;
	unsigned long addr;

	/*
	 * If we've been called in to before initialization has
	 * completed, bail out immediately.
	 */
	if (!dwarf_unwinder_ready)
		return NULL;

	/*
	 * If we're starting at the top of the stack we need get the
	 * contents of a physical register to get the CFA in order to
	 * begin the virtual unwinding of the stack.
	 *
	 * NOTE: the return address is guaranteed to be setup by the
	 * time this function makes its first function call.
	 */
	if (!pc || !prev)
		pc = (unsigned long)current_text_addr();

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
	/*
	 * If our stack has been patched by the function graph tracer
	 * then we might see the address of return_to_handler() where we
	 * expected to find the real return address.
	 */
	if (pc == (unsigned long)&return_to_handler) {
		int index = current->curr_ret_stack;

		/*
		 * We currently have no way of tracking how many
		 * return_to_handler()'s we've seen. If there is more
		 * than one patched return address on our stack,
		 * complain loudly.
		 */
		WARN_ON(index > 0);

		pc = current->ret_stack[index].ret;
	}
#endif

	frame = mempool_alloc(dwarf_frame_pool, GFP_ATOMIC);
	if (!frame) {
		printk(KERN_ERR "Unable to allocate a dwarf frame\n");
		UNWINDER_BUG();
	}

	INIT_LIST_HEAD(&frame->reg_list);
	frame->flags = 0;
	frame->prev = prev;
	frame->return_addr = 0;

	fde = dwarf_lookup_fde(pc);
	if (!fde) {
		/*
		 * This is our normal exit path. There are two reasons
		 * why we might exit here,
		 *
		 *	a) pc has no asscociated DWARF frame info and so
		 *	we don't know how to unwind this frame. This is
		 *	usually the case when we're trying to unwind a
		 *	frame that was called from some assembly code
		 *	that has no DWARF info, e.g. syscalls.
		 *
		 *	b) the DEBUG info for pc is bogus. There's
		 *	really no way to distinguish this case from the
		 *	case above, which sucks because we could print a
		 *	warning here.
		 */
		goto bail;
	}

	cie = dwarf_lookup_cie(fde->cie_pointer);

	frame->pc = fde->initial_location;

	/* CIE initial instructions */
	dwarf_cfa_execute_insns(cie->initial_instructions,
				cie->instructions_end, cie, fde,
				frame, pc);

	/* FDE instructions */
	dwarf_cfa_execute_insns(fde->instructions, fde->end, cie,
				fde, frame, pc);

	/* Calculate the CFA */
	switch (frame->flags) {
	case DWARF_FRAME_CFA_REG_OFFSET:
		if (prev) {
			reg = dwarf_frame_reg(prev, frame->cfa_register);
			UNWINDER_BUG_ON(!reg);
			UNWINDER_BUG_ON(reg->flags != DWARF_REG_OFFSET);

			addr = prev->cfa + reg->addr;
			frame->cfa = __raw_readl(addr);

		} else {
			/*
			 * Again, we're starting from the top of the
			 * stack. We need to physically read
			 * the contents of a register in order to get
			 * the Canonical Frame Address for this
			 * function.
			 */
			frame->cfa = dwarf_read_arch_reg(frame->cfa_register);
		}

		frame->cfa += frame->cfa_offset;
		break;
	default:
		UNWINDER_BUG();
	}

	reg = dwarf_frame_reg(frame, DWARF_ARCH_RA_REG);

	/*
	 * If we haven't seen the return address register or the return
	 * address column is undefined then we must assume that this is
	 * the end of the callstack.
	 */
	if (!reg || reg->flags == DWARF_UNDEFINED)
		goto bail;

	UNWINDER_BUG_ON(reg->flags != DWARF_REG_OFFSET);

	addr = frame->cfa + reg->addr;
	frame->return_addr = __raw_readl(addr);

	/*
	 * Ah, the joys of unwinding through interrupts.
	 *
	 * Interrupts are tricky - the DWARF info needs to be _really_
	 * accurate and unfortunately I'm seeing a lot of bogus DWARF
	 * info. For example, I've seen interrupts occur in epilogues
	 * just after the frame pointer (r14) had been restored. The
	 * problem was that the DWARF info claimed that the CFA could be
	 * reached by using the value of the frame pointer before it was
	 * restored.
	 *
	 * So until the compiler can be trusted to produce reliable
	 * DWARF info when it really matters, let's stop unwinding once
	 * we've calculated the function that was interrupted.
	 */
	if (prev && prev->pc == (unsigned long)ret_from_irq)
		frame->return_addr = 0;

	return frame;

bail:
	dwarf_free_frame(frame);
	return NULL;
}

static int dwarf_parse_cie(void *entry, void *p, unsigned long len,
			   unsigned char *end, struct module *mod)
{
	struct rb_node **rb_node = &cie_root.rb_node;
	struct rb_node *parent = *rb_node;
	struct dwarf_cie *cie;
	unsigned long flags;
	int count;

	cie = kzalloc(sizeof(*cie), GFP_KERNEL);
	if (!cie)
		return -ENOMEM;

	cie->length = len;

	/*
	 * Record the offset into the .eh_frame section
	 * for this CIE. It allows this CIE to be
	 * quickly and easily looked up from the
	 * corresponding FDE.
	 */
	cie->cie_pointer = (unsigned long)entry;

	cie->version = *(char *)p++;
	UNWINDER_BUG_ON(cie->version != 1);

	cie->augmentation = p;
	p += strlen(cie->augmentation) + 1;

	count = dwarf_read_uleb128(p, &cie->code_alignment_factor);
	p += count;

	count = dwarf_read_leb128(p, &cie->data_alignment_factor);
	p += count;

	/*
	 * Which column in the rule table contains the
	 * return address?
	 */
	if (cie->version == 1) {
		cie->return_address_reg = __raw_readb(p);
		p++;
	} else {
		count = dwarf_read_uleb128(p, &cie->return_address_reg);
		p += count;
	}

	if (cie->augmentation[0] == 'z') {
		unsigned int length, count;
		cie->flags |= DWARF_CIE_Z_AUGMENTATION;

		count = dwarf_read_uleb128(p, &length);
		p += count;

		UNWINDER_BUG_ON((unsigned char *)p > end);

		cie->initial_instructions = p + length;
		cie->augmentation++;
	}

	while (*cie->augmentation) {
		/*
		 * "L" indicates a byte showing how the
		 * LSDA pointer is encoded. Skip it.
		 */
		if (*cie->augmentation == 'L') {
			p++;
			cie->augmentation++;
		} else if (*cie->augmentation == 'R') {
			/*
			 * "R" indicates a byte showing
			 * how FDE addresses are
			 * encoded.
			 */
			cie->encoding = *(char *)p++;
			cie->augmentation++;
		} else if (*cie->augmentation == 'P') {
			/*
			 * "R" indicates a personality
			 * routine in the CIE
			 * augmentation.
			 */
			UNWINDER_BUG();
		} else if (*cie->augmentation == 'S') {
			UNWINDER_BUG();
		} else {
			/*
			 * Unknown augmentation. Assume
			 * 'z' augmentation.
			 */
			p = cie->initial_instructions;
			UNWINDER_BUG_ON(!p);
			break;
		}
	}

	cie->initial_instructions = p;
	cie->instructions_end = end;

	/* Add to list */
	spin_lock_irqsave(&dwarf_cie_lock, flags);

	while (*rb_node) {
		struct dwarf_cie *cie_tmp;

		cie_tmp = rb_entry(*rb_node, struct dwarf_cie, node);

		parent = *rb_node;

		if (cie->cie_pointer < cie_tmp->cie_pointer)
			rb_node = &parent->rb_left;
		else if (cie->cie_pointer >= cie_tmp->cie_pointer)
			rb_node = &parent->rb_right;
		else
			WARN_ON(1);
	}

	rb_link_node(&cie->node, parent, rb_node);
	rb_insert_color(&cie->node, &cie_root);

#ifdef CONFIG_MODULES
	if (mod != NULL)
		list_add_tail(&cie->link, &mod->arch.cie_list);
#endif

	spin_unlock_irqrestore(&dwarf_cie_lock, flags);

	return 0;
}

static int dwarf_parse_fde(void *entry, u32 entry_type,
			   void *start, unsigned long len,
			   unsigned char *end, struct module *mod)
{
	struct rb_node **rb_node = &fde_root.rb_node;
	struct rb_node *parent = *rb_node;
	struct dwarf_fde *fde;
	struct dwarf_cie *cie;
	unsigned long flags;
	int count;
	void *p = start;

	fde = kzalloc(sizeof(*fde), GFP_KERNEL);
	if (!fde)
		return -ENOMEM;

	fde->length = len;

	/*
	 * In a .eh_frame section the CIE pointer is the
	 * delta between the address within the FDE
	 */
	fde->cie_pointer = (unsigned long)(p - entry_type - 4);

	cie = dwarf_lookup_cie(fde->cie_pointer);
	fde->cie = cie;

	if (cie->encoding)
		count = dwarf_read_encoded_value(p, &fde->initial_location,
						 cie->encoding);
	else
		count = dwarf_read_addr(p, &fde->initial_location);

	p += count;

	if (cie->encoding)
		count = dwarf_read_encoded_value(p, &fde->address_range,
						 cie->encoding & 0x0f);
	else
		count = dwarf_read_addr(p, &fde->address_range);

	p += count;

	if (fde->cie->flags & DWARF_CIE_Z_AUGMENTATION) {
		unsigned int length;
		count = dwarf_read_uleb128(p, &length);
		p += count + length;
	}

	/* Call frame instructions. */
	fde->instructions = p;
	fde->end = end;

	/* Add to list. */
	spin_lock_irqsave(&dwarf_fde_lock, flags);

	while (*rb_node) {
		struct dwarf_fde *fde_tmp;
		unsigned long tmp_start, tmp_end;
		unsigned long start, end;

		fde_tmp = rb_entry(*rb_node, struct dwarf_fde, node);

		start = fde->initial_location;
		end = fde->initial_location + fde->address_range;

		tmp_start = fde_tmp->initial_location;
		tmp_end = fde_tmp->initial_location + fde_tmp->address_range;

		parent = *rb_node;

		if (start < tmp_start)
			rb_node = &parent->rb_left;
		else if (start >= tmp_end)
			rb_node = &parent->rb_right;
		else
			WARN_ON(1);
	}

	rb_link_node(&fde->node, parent, rb_node);
	rb_insert_color(&fde->node, &fde_root);

#ifdef CONFIG_MODULES
	if (mod != NULL)
		list_add_tail(&fde->link, &mod->arch.fde_list);
#endif

	spin_unlock_irqrestore(&dwarf_fde_lock, flags);

	return 0;
}

static void dwarf_unwinder_dump(struct task_struct *task,
				struct pt_regs *regs,
				unsigned long *sp,
				const struct stacktrace_ops *ops,
				void *data)
{
	struct dwarf_frame *frame, *_frame;
	unsigned long return_addr;

	_frame = NULL;
	return_addr = 0;

	while (1) {
		frame = dwarf_unwind_stack(return_addr, _frame);

		if (_frame)
			dwarf_free_frame(_frame);

		_frame = frame;

		if (!frame || !frame->return_addr)
			break;

		return_addr = frame->return_addr;
		ops->address(data, return_addr, 1);
	}

	if (frame)
		dwarf_free_frame(frame);
}

static struct unwinder dwarf_unwinder = {
	.name = "dwarf-unwinder",
	.dump = dwarf_unwinder_dump,
	.rating = 150,
};

static void __init dwarf_unwinder_cleanup(void)
{
	struct dwarf_fde *fde, *next_fde;
	struct dwarf_cie *cie, *next_cie;

	/*
	 * Deallocate all the memory allocated for the DWARF unwinder.
	 * Traverse all the FDE/CIE lists and remove and free all the
	 * memory associated with those data structures.
	 */
	rbtree_postorder_for_each_entry_safe(fde, next_fde, &fde_root, node)
		kfree(fde);

	rbtree_postorder_for_each_entry_safe(cie, next_cie, &cie_root, node)
		kfree(cie);

	mempool_destroy(dwarf_reg_pool);
	mempool_destroy(dwarf_frame_pool);
	kmem_cache_destroy(dwarf_reg_cachep);
	kmem_cache_destroy(dwarf_frame_cachep);
}

/**
 *	dwarf_parse_section - parse DWARF section
 *	@eh_frame_start: start address of the .eh_frame section
 *	@eh_frame_end: end address of the .eh_frame section
 *	@mod: the kernel module containing the .eh_frame section
 *
 *	Parse the information in a .eh_frame section.
 */
static int dwarf_parse_section(char *eh_frame_start, char *eh_frame_end,
			       struct module *mod)
{
	u32 entry_type;
	void *p, *entry;
	int count, err = 0;
	unsigned long len = 0;
	unsigned int c_entries, f_entries;
	unsigned char *end;

	c_entries = 0;
	f_entries = 0;
	entry = eh_frame_start;

	while ((char *)entry < eh_frame_end) {
		p = entry;

		count = dwarf_entry_len(p, &len);
		if (count == 0) {
			/*
			 * We read a bogus length field value. There is
			 * nothing we can do here apart from disabling
			 * the DWARF unwinder. We can't even skip this
			 * entry and move to the next one because 'len'
			 * tells us where our next entry is.
			 */
			err = -EINVAL;
			goto out;
		} else
			p += count;

		/* initial length does not include itself */
		end = p + len;

		entry_type = get_unaligned((u32 *)p);
		p += 4;

		if (entry_type == DW_EH_FRAME_CIE) {
			err = dwarf_parse_cie(entry, p, len, end, mod);
			if (err < 0)
				goto out;
			else
				c_entries++;
		} else {
			err = dwarf_parse_fde(entry, entry_type, p, len,
					      end, mod);
			if (err < 0)
				goto out;
			else
				f_entries++;
		}

		entry = (char *)entry + len + 4;
	}

	printk(KERN_INFO "DWARF unwinder initialised: read %u CIEs, %u FDEs\n",
	       c_entries, f_entries);

	return 0;

out:
	return err;
}

#ifdef CONFIG_MODULES
int module_dwarf_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
			  struct module *me)
{
	unsigned int i, err;
	unsigned long start, end;
	char *secstrings = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;

	start = end = 0;

	for (i = 1; i < hdr->e_shnum; i++) {
		/* Alloc bit cleared means "ignore it." */
		if ((sechdrs[i].sh_flags & SHF_ALLOC)
		    && !strcmp(secstrings+sechdrs[i].sh_name, ".eh_frame")) {
			start = sechdrs[i].sh_addr;
			end = start + sechdrs[i].sh_size;
			break;
		}
	}

	/* Did we find the .eh_frame section? */
	if (i != hdr->e_shnum) {
		INIT_LIST_HEAD(&me->arch.cie_list);
		INIT_LIST_HEAD(&me->arch.fde_list);
		err = dwarf_parse_section((char *)start, (char *)end, me);
		if (err) {
			printk(KERN_WARNING "%s: failed to parse DWARF info\n",
			       me->name);
			return err;
		}
	}

	return 0;
}

/**
 *	module_dwarf_cleanup - remove FDE/CIEs associated with @mod
 *	@mod: the module that is being unloaded
 *
 *	Remove any FDEs and CIEs from the global lists that came from
 *	@mod's .eh_frame section because @mod is being unloaded.
 */
void module_dwarf_cleanup(struct module *mod)
{
	struct dwarf_fde *fde, *ftmp;
	struct dwarf_cie *cie, *ctmp;
	unsigned long flags;

	spin_lock_irqsave(&dwarf_cie_lock, flags);

	list_for_each_entry_safe(cie, ctmp, &mod->arch.cie_list, link) {
		list_del(&cie->link);
		rb_erase(&cie->node, &cie_root);
		kfree(cie);
	}

	spin_unlock_irqrestore(&dwarf_cie_lock, flags);

	spin_lock_irqsave(&dwarf_fde_lock, flags);

	list_for_each_entry_safe(fde, ftmp, &mod->arch.fde_list, link) {
		list_del(&fde->link);
		rb_erase(&fde->node, &fde_root);
		kfree(fde);
	}

	spin_unlock_irqrestore(&dwarf_fde_lock, flags);
}
#endif /* CONFIG_MODULES */

/**
 *	dwarf_unwinder_init - initialise the dwarf unwinder
 *
 *	Build the data structures describing the .dwarf_frame section to
 *	make it easier to lookup CIE and FDE entries. Because the
 *	.eh_frame section is packed as tightly as possible it is not
 *	easy to lookup the FDE for a given PC, so we build a list of FDE
 *	and CIE entries that make it easier.
 */
static int __init dwarf_unwinder_init(void)
{
	int err = -ENOMEM;

	dwarf_frame_cachep = kmem_cache_create("dwarf_frames",
			sizeof(struct dwarf_frame), 0,
			SLAB_PANIC | SLAB_HWCACHE_ALIGN, NULL);

	dwarf_reg_cachep = kmem_cache_create("dwarf_regs",
			sizeof(struct dwarf_reg), 0,
			SLAB_PANIC | SLAB_HWCACHE_ALIGN, NULL);

	dwarf_frame_pool = mempool_create_slab_pool(DWARF_FRAME_MIN_REQ,
						    dwarf_frame_cachep);
	if (!dwarf_frame_pool)
		goto out;

	dwarf_reg_pool = mempool_create_slab_pool(DWARF_REG_MIN_REQ,
						  dwarf_reg_cachep);
	if (!dwarf_reg_pool)
		goto out;

	err = dwarf_parse_section(__start_eh_frame, __stop_eh_frame, NULL);
	if (err)
		goto out;

	err = unwinder_register(&dwarf_unwinder);
	if (err)
		goto out;

	dwarf_unwinder_ready = 1;

	return 0;

out:
	printk(KERN_ERR "Failed to initialise DWARF unwinder: %d\n", err);
	dwarf_unwinder_cleanup();
	return err;
}
early_initcall(dwarf_unwinder_init);