summaryrefslogtreecommitdiffstats
path: root/tools/lib/bpf/btf_dump.c
blob: 61aa2c47fbd5e93102c650bd4c4c4a04d1ca1017 (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
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)

/*
 * BTF-to-C type converter.
 *
 * Copyright (c) 2019 Facebook
 */

#include <stdbool.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <linux/err.h>
#include <linux/btf.h>
#include <linux/kernel.h>
#include "btf.h"
#include "hashmap.h"
#include "libbpf.h"
#include "libbpf_internal.h"

static const char PREFIXES[] = "\t\t\t\t\t\t\t\t\t\t\t\t\t";
static const size_t PREFIX_CNT = sizeof(PREFIXES) - 1;

static const char *pfx(int lvl)
{
	return lvl >= PREFIX_CNT ? PREFIXES : &PREFIXES[PREFIX_CNT - lvl];
}

enum btf_dump_type_order_state {
	NOT_ORDERED,
	ORDERING,
	ORDERED,
};

enum btf_dump_type_emit_state {
	NOT_EMITTED,
	EMITTING,
	EMITTED,
};

/* per-type auxiliary state */
struct btf_dump_type_aux_state {
	/* topological sorting state */
	enum btf_dump_type_order_state order_state: 2;
	/* emitting state used to determine the need for forward declaration */
	enum btf_dump_type_emit_state emit_state: 2;
	/* whether forward declaration was already emitted */
	__u8 fwd_emitted: 1;
	/* whether unique non-duplicate name was already assigned */
	__u8 name_resolved: 1;
	/* whether type is referenced from any other type */
	__u8 referenced: 1;
};

struct btf_dump {
	const struct btf *btf;
	const struct btf_ext *btf_ext;
	btf_dump_printf_fn_t printf_fn;
	struct btf_dump_opts opts;
	int ptr_sz;
	bool strip_mods;
	int last_id;

	/* per-type auxiliary state */
	struct btf_dump_type_aux_state *type_states;
	size_t type_states_cap;
	/* per-type optional cached unique name, must be freed, if present */
	const char **cached_names;
	size_t cached_names_cap;

	/* topo-sorted list of dependent type definitions */
	__u32 *emit_queue;
	int emit_queue_cap;
	int emit_queue_cnt;

	/*
	 * stack of type declarations (e.g., chain of modifiers, arrays,
	 * funcs, etc)
	 */
	__u32 *decl_stack;
	int decl_stack_cap;
	int decl_stack_cnt;

	/* maps struct/union/enum name to a number of name occurrences */
	struct hashmap *type_names;
	/*
	 * maps typedef identifiers and enum value names to a number of such
	 * name occurrences
	 */
	struct hashmap *ident_names;
};

static size_t str_hash_fn(const void *key, void *ctx)
{
	return str_hash(key);
}

static bool str_equal_fn(const void *a, const void *b, void *ctx)
{
	return strcmp(a, b) == 0;
}

static const char *btf_name_of(const struct btf_dump *d, __u32 name_off)
{
	return btf__name_by_offset(d->btf, name_off);
}

static void btf_dump_printf(const struct btf_dump *d, const char *fmt, ...)
{
	va_list args;

	va_start(args, fmt);
	d->printf_fn(d->opts.ctx, fmt, args);
	va_end(args);
}

static int btf_dump_mark_referenced(struct btf_dump *d);
static int btf_dump_resize(struct btf_dump *d);

struct btf_dump *btf_dump__new(const struct btf *btf,
			       const struct btf_ext *btf_ext,
			       const struct btf_dump_opts *opts,
			       btf_dump_printf_fn_t printf_fn)
{
	struct btf_dump *d;
	int err;

	d = calloc(1, sizeof(struct btf_dump));
	if (!d)
		return ERR_PTR(-ENOMEM);

	d->btf = btf;
	d->btf_ext = btf_ext;
	d->printf_fn = printf_fn;
	d->opts.ctx = opts ? opts->ctx : NULL;
	d->ptr_sz = btf__pointer_size(btf) ? : sizeof(void *);

	d->type_names = hashmap__new(str_hash_fn, str_equal_fn, NULL);
	if (IS_ERR(d->type_names)) {
		err = PTR_ERR(d->type_names);
		d->type_names = NULL;
		goto err;
	}
	d->ident_names = hashmap__new(str_hash_fn, str_equal_fn, NULL);
	if (IS_ERR(d->ident_names)) {
		err = PTR_ERR(d->ident_names);
		d->ident_names = NULL;
		goto err;
	}

	err = btf_dump_resize(d);
	if (err)
		goto err;

	return d;
err:
	btf_dump__free(d);
	return ERR_PTR(err);
}

static int btf_dump_resize(struct btf_dump *d)
{
	int err, last_id = btf__get_nr_types(d->btf);

	if (last_id <= d->last_id)
		return 0;

	if (btf_ensure_mem((void **)&d->type_states, &d->type_states_cap,
			   sizeof(*d->type_states), last_id + 1))
		return -ENOMEM;
	if (btf_ensure_mem((void **)&d->cached_names, &d->cached_names_cap,
			   sizeof(*d->cached_names), last_id + 1))
		return -ENOMEM;

	if (d->last_id == 0) {
		/* VOID is special */
		d->type_states[0].order_state = ORDERED;
		d->type_states[0].emit_state = EMITTED;
	}

	/* eagerly determine referenced types for anon enums */
	err = btf_dump_mark_referenced(d);
	if (err)
		return err;

	d->last_id = last_id;
	return 0;
}

static void btf_dump_free_names(struct hashmap *map)
{
	size_t bkt;
	struct hashmap_entry *cur;

	hashmap__for_each_entry(map, cur, bkt)
		free((void *)cur->key);

	hashmap__free(map);
}

void btf_dump__free(struct btf_dump *d)
{
	int i;

	if (IS_ERR_OR_NULL(d))
		return;

	free(d->type_states);
	if (d->cached_names) {
		/* any set cached name is owned by us and should be freed */
		for (i = 0; i <= d->last_id; i++) {
			if (d->cached_names[i])
				free((void *)d->cached_names[i]);
		}
	}
	free(d->cached_names);
	free(d->emit_queue);
	free(d->decl_stack);
	btf_dump_free_names(d->type_names);
	btf_dump_free_names(d->ident_names);

	free(d);
}

static int btf_dump_order_type(struct btf_dump *d, __u32 id, bool through_ptr);
static void btf_dump_emit_type(struct btf_dump *d, __u32 id, __u32 cont_id);

/*
 * Dump BTF type in a compilable C syntax, including all the necessary
 * dependent types, necessary for compilation. If some of the dependent types
 * were already emitted as part of previous btf_dump__dump_type() invocation
 * for another type, they won't be emitted again. This API allows callers to
 * filter out BTF types according to user-defined criterias and emitted only
 * minimal subset of types, necessary to compile everything. Full struct/union
 * definitions will still be emitted, even if the only usage is through
 * pointer and could be satisfied with just a forward declaration.
 *
 * Dumping is done in two high-level passes:
 *   1. Topologically sort type definitions to satisfy C rules of compilation.
 *   2. Emit type definitions in C syntax.
 *
 * Returns 0 on success; <0, otherwise.
 */
int btf_dump__dump_type(struct btf_dump *d, __u32 id)
{
	int err, i;

	if (id > btf__get_nr_types(d->btf))
		return -EINVAL;

	err = btf_dump_resize(d);
	if (err)
		return err;

	d->emit_queue_cnt = 0;
	err = btf_dump_order_type(d, id, false);
	if (err < 0)
		return err;

	for (i = 0; i < d->emit_queue_cnt; i++)
		btf_dump_emit_type(d, d->emit_queue[i], 0 /*top-level*/);

	return 0;
}

/*
 * Mark all types that are referenced from any other type. This is used to
 * determine top-level anonymous enums that need to be emitted as an
 * independent type declarations.
 * Anonymous enums come in two flavors: either embedded in a struct's field
 * definition, in which case they have to be declared inline as part of field
 * type declaration; or as a top-level anonymous enum, typically used for
 * declaring global constants. It's impossible to distinguish between two
 * without knowning whether given enum type was referenced from other type:
 * top-level anonymous enum won't be referenced by anything, while embedded
 * one will.
 */
static int btf_dump_mark_referenced(struct btf_dump *d)
{
	int i, j, n = btf__get_nr_types(d->btf);
	const struct btf_type *t;
	__u16 vlen;

	for (i = d->last_id + 1; i <= n; i++) {
		t = btf__type_by_id(d->btf, i);
		vlen = btf_vlen(t);

		switch (btf_kind(t)) {
		case BTF_KIND_INT:
		case BTF_KIND_ENUM:
		case BTF_KIND_FWD:
			break;

		case BTF_KIND_VOLATILE:
		case BTF_KIND_CONST:
		case BTF_KIND_RESTRICT:
		case BTF_KIND_PTR:
		case BTF_KIND_TYPEDEF:
		case BTF_KIND_FUNC:
		case BTF_KIND_VAR:
			d->type_states[t->type].referenced = 1;
			break;

		case BTF_KIND_ARRAY: {
			const struct btf_array *a = btf_array(t);

			d->type_states[a->index_type].referenced = 1;
			d->type_states[a->type].referenced = 1;
			break;
		}
		case BTF_KIND_STRUCT:
		case BTF_KIND_UNION: {
			const struct btf_member *m = btf_members(t);

			for (j = 0; j < vlen; j++, m++)
				d->type_states[m->type].referenced = 1;
			break;
		}
		case BTF_KIND_FUNC_PROTO: {
			const struct btf_param *p = btf_params(t);

			for (j = 0; j < vlen; j++, p++)
				d->type_states[p->type].referenced = 1;
			break;
		}
		case BTF_KIND_DATASEC: {
			const struct btf_var_secinfo *v = btf_var_secinfos(t);

			for (j = 0; j < vlen; j++, v++)
				d->type_states[v->type].referenced = 1;
			break;
		}
		default:
			return -EINVAL;
		}
	}
	return 0;
}

static int btf_dump_add_emit_queue_id(struct btf_dump *d, __u32 id)
{
	__u32 *new_queue;
	size_t new_cap;

	if (d->emit_queue_cnt >= d->emit_queue_cap) {
		new_cap = max(16, d->emit_queue_cap * 3 / 2);
		new_queue = libbpf_reallocarray(d->emit_queue, new_cap, sizeof(new_queue[0]));
		if (!new_queue)
			return -ENOMEM;
		d->emit_queue = new_queue;
		d->emit_queue_cap = new_cap;
	}

	d->emit_queue[d->emit_queue_cnt++] = id;
	return 0;
}

/*
 * Determine order of emitting dependent types and specified type to satisfy
 * C compilation rules.  This is done through topological sorting with an
 * additional complication which comes from C rules. The main idea for C is
 * that if some type is "embedded" into a struct/union, it's size needs to be
 * known at the time of definition of containing type. E.g., for:
 *
 *	struct A {};
 *	struct B { struct A x; }
 *
 * struct A *HAS* to be defined before struct B, because it's "embedded",
 * i.e., it is part of struct B layout. But in the following case:
 *
 *	struct A;
 *	struct B { struct A *x; }
 *	struct A {};
 *
 * it's enough to just have a forward declaration of struct A at the time of
 * struct B definition, as struct B has a pointer to struct A, so the size of
 * field x is known without knowing struct A size: it's sizeof(void *).
 *
 * Unfortunately, there are some trickier cases we need to handle, e.g.:
 *
 *	struct A {}; // if this was forward-declaration: compilation error
 *	struct B {
 *		struct { // anonymous struct
 *			struct A y;
 *		} *x;
 *	};
 *
 * In this case, struct B's field x is a pointer, so it's size is known
 * regardless of the size of (anonymous) struct it points to. But because this
 * struct is anonymous and thus defined inline inside struct B, *and* it
 * embeds struct A, compiler requires full definition of struct A to be known
 * before struct B can be defined. This creates a transitive dependency
 * between struct A and struct B. If struct A was forward-declared before
 * struct B definition and fully defined after struct B definition, that would
 * trigger compilation error.
 *
 * All this means that while we are doing topological sorting on BTF type
 * graph, we need to determine relationships between different types (graph
 * nodes):
 *   - weak link (relationship) between X and Y, if Y *CAN* be
 *   forward-declared at the point of X definition;
 *   - strong link, if Y *HAS* to be fully-defined before X can be defined.
 *
 * The rule is as follows. Given a chain of BTF types from X to Y, if there is
 * BTF_KIND_PTR type in the chain and at least one non-anonymous type
 * Z (excluding X, including Y), then link is weak. Otherwise, it's strong.
 * Weak/strong relationship is determined recursively during DFS traversal and
 * is returned as a result from btf_dump_order_type().
 *
 * btf_dump_order_type() is trying to avoid unnecessary forward declarations,
 * but it is not guaranteeing that no extraneous forward declarations will be
 * emitted.
 *
 * To avoid extra work, algorithm marks some of BTF types as ORDERED, when
 * it's done with them, but not for all (e.g., VOLATILE, CONST, RESTRICT,
 * ARRAY, FUNC_PROTO), as weak/strong semantics for those depends on the
 * entire graph path, so depending where from one came to that BTF type, it
 * might cause weak or strong ordering. For types like STRUCT/UNION/INT/ENUM,
 * once they are processed, there is no need to do it again, so they are
 * marked as ORDERED. We can mark PTR as ORDERED as well, as it semi-forces
 * weak link, unless subsequent referenced STRUCT/UNION/ENUM is anonymous. But
 * in any case, once those are processed, no need to do it again, as the
 * result won't change.
 *
 * Returns:
 *   - 1, if type is part of strong link (so there is strong topological
 *   ordering requirements);
 *   - 0, if type is part of weak link (so can be satisfied through forward
 *   declaration);
 *   - <0, on error (e.g., unsatisfiable type loop detected).
 */
static int btf_dump_order_type(struct btf_dump *d, __u32 id, bool through_ptr)
{
	/*
	 * Order state is used to detect strong link cycles, but only for BTF
	 * kinds that are or could be an independent definition (i.e.,
	 * stand-alone fwd decl, enum, typedef, struct, union). Ptrs, arrays,
	 * func_protos, modifiers are just means to get to these definitions.
	 * Int/void don't need definitions, they are assumed to be always
	 * properly defined.  We also ignore datasec, var, and funcs for now.
	 * So for all non-defining kinds, we never even set ordering state,
	 * for defining kinds we set ORDERING and subsequently ORDERED if it
	 * forms a strong link.
	 */
	struct btf_dump_type_aux_state *tstate = &d->type_states[id];
	const struct btf_type *t;
	__u16 vlen;
	int err, i;

	/* return true, letting typedefs know that it's ok to be emitted */
	if (tstate->order_state == ORDERED)
		return 1;

	t = btf__type_by_id(d->btf, id);

	if (tstate->order_state == ORDERING) {
		/* type loop, but resolvable through fwd declaration */
		if (btf_is_composite(t) && through_ptr && t->name_off != 0)
			return 0;
		pr_warn("unsatisfiable type cycle, id:[%u]\n", id);
		return -ELOOP;
	}

	switch (btf_kind(t)) {
	case BTF_KIND_INT:
		tstate->order_state = ORDERED;
		return 0;

	case BTF_KIND_PTR:
		err = btf_dump_order_type(d, t->type, true);
		tstate->order_state = ORDERED;
		return err;

	case BTF_KIND_ARRAY:
		return btf_dump_order_type(d, btf_array(t)->type, false);

	case BTF_KIND_STRUCT:
	case BTF_KIND_UNION: {
		const struct btf_member *m = btf_members(t);
		/*
		 * struct/union is part of strong link, only if it's embedded
		 * (so no ptr in a path) or it's anonymous (so has to be
		 * defined inline, even if declared through ptr)
		 */
		if (through_ptr && t->name_off != 0)
			return 0;

		tstate->order_state = ORDERING;

		vlen = btf_vlen(t);
		for (i = 0; i < vlen; i++, m++) {
			err = btf_dump_order_type(d, m->type, false);
			if (err < 0)
				return err;
		}

		if (t->name_off != 0) {
			err = btf_dump_add_emit_queue_id(d, id);
			if (err < 0)
				return err;
		}

		tstate->order_state = ORDERED;
		return 1;
	}
	case BTF_KIND_ENUM:
	case BTF_KIND_FWD:
		/*
		 * non-anonymous or non-referenced enums are top-level
		 * declarations and should be emitted. Same logic can be
		 * applied to FWDs, it won't hurt anyways.
		 */
		if (t->name_off != 0 || !tstate->referenced) {
			err = btf_dump_add_emit_queue_id(d, id);
			if (err)
				return err;
		}
		tstate->order_state = ORDERED;
		return 1;

	case BTF_KIND_TYPEDEF: {
		int is_strong;

		is_strong = btf_dump_order_type(d, t->type, through_ptr);
		if (is_strong < 0)
			return is_strong;

		/* typedef is similar to struct/union w.r.t. fwd-decls */
		if (through_ptr && !is_strong)
			return 0;

		/* typedef is always a named definition */
		err = btf_dump_add_emit_queue_id(d, id);
		if (err)
			return err;

		d->type_states[id].order_state = ORDERED;
		return 1;
	}
	case BTF_KIND_VOLATILE:
	case BTF_KIND_CONST:
	case BTF_KIND_RESTRICT:
		return btf_dump_order_type(d, t->type, through_ptr);

	case BTF_KIND_FUNC_PROTO: {
		const struct btf_param *p = btf_params(t);
		bool is_strong;

		err = btf_dump_order_type(d, t->type, through_ptr);
		if (err < 0)
			return err;
		is_strong = err > 0;

		vlen = btf_vlen(t);
		for (i = 0; i < vlen; i++, p++) {
			err = btf_dump_order_type(d, p->type, through_ptr);
			if (err < 0)
				return err;
			if (err > 0)
				is_strong = true;
		}
		return is_strong;
	}
	case BTF_KIND_FUNC:
	case BTF_KIND_VAR:
	case BTF_KIND_DATASEC:
		d->type_states[id].order_state = ORDERED;
		return 0;

	default:
		return -EINVAL;
	}
}

static void btf_dump_emit_missing_aliases(struct btf_dump *d, __u32 id,
					  const struct btf_type *t);

static void btf_dump_emit_struct_fwd(struct btf_dump *d, __u32 id,
				     const struct btf_type *t);
static void btf_dump_emit_struct_def(struct btf_dump *d, __u32 id,
				     const struct btf_type *t, int lvl);

static void btf_dump_emit_enum_fwd(struct btf_dump *d, __u32 id,
				   const struct btf_type *t);
static void btf_dump_emit_enum_def(struct btf_dump *d, __u32 id,
				   const struct btf_type *t, int lvl);

static void btf_dump_emit_fwd_def(struct btf_dump *d, __u32 id,
				  const struct btf_type *t);

static void btf_dump_emit_typedef_def(struct btf_dump *d, __u32 id,
				      const struct btf_type *t, int lvl);

/* a local view into a shared stack */
struct id_stack {
	const __u32 *ids;
	int cnt;
};

static void btf_dump_emit_type_decl(struct btf_dump *d, __u32 id,
				    const char *fname, int lvl);
static void btf_dump_emit_type_chain(struct btf_dump *d,
				     struct id_stack *decl_stack,
				     const char *fname, int lvl);

static const char *btf_dump_type_name(struct btf_dump *d, __u32 id);
static const char *btf_dump_ident_name(struct btf_dump *d, __u32 id);
static size_t btf_dump_name_dups(struct btf_dump *d, struct hashmap *name_map,
				 const char *orig_name);

static bool btf_dump_is_blacklisted(struct btf_dump *d, __u32 id)
{
	const struct btf_type *t = btf__type_by_id(d->btf, id);

	/* __builtin_va_list is a compiler built-in, which causes compilation
	 * errors, when compiling w/ different compiler, then used to compile
	 * original code (e.g., GCC to compile kernel, Clang to use generated
	 * C header from BTF). As it is built-in, it should be already defined
	 * properly internally in compiler.
	 */
	if (t->name_off == 0)
		return false;
	return strcmp(btf_name_of(d, t->name_off), "__builtin_va_list") == 0;
}

/*
 * Emit C-syntax definitions of types from chains of BTF types.
 *
 * High-level handling of determining necessary forward declarations are handled
 * by btf_dump_emit_type() itself, but all nitty-gritty details of emitting type
 * declarations/definitions in C syntax  are handled by a combo of
 * btf_dump_emit_type_decl()/btf_dump_emit_type_chain() w/ delegation to
 * corresponding btf_dump_emit_*_{def,fwd}() functions.
 *
 * We also keep track of "containing struct/union type ID" to determine when
 * we reference it from inside and thus can avoid emitting unnecessary forward
 * declaration.
 *
 * This algorithm is designed in such a way, that even if some error occurs
 * (either technical, e.g., out of memory, or logical, i.e., malformed BTF
 * that doesn't comply to C rules completely), algorithm will try to proceed
 * and produce as much meaningful output as possible.
 */
static void btf_dump_emit_type(struct btf_dump *d, __u32 id, __u32 cont_id)
{
	struct btf_dump_type_aux_state *tstate = &d->type_states[id];
	bool top_level_def = cont_id == 0;
	const struct btf_type *t;
	__u16 kind;

	if (tstate->emit_state == EMITTED)
		return;

	t = btf__type_by_id(d->btf, id);
	kind = btf_kind(t);

	if (tstate->emit_state == EMITTING) {
		if (tstate->fwd_emitted)
			return;

		switch (kind) {
		case BTF_KIND_STRUCT:
		case BTF_KIND_UNION:
			/*
			 * if we are referencing a struct/union that we are
			 * part of - then no need for fwd declaration
			 */
			if (id == cont_id)
				return;
			if (t->name_off == 0) {
				pr_warn("anonymous struct/union loop, id:[%u]\n",
					id);
				return;
			}
			btf_dump_emit_struct_fwd(d, id, t);
			btf_dump_printf(d, ";\n\n");
			tstate->fwd_emitted = 1;
			break;
		case BTF_KIND_TYPEDEF:
			/*
			 * for typedef fwd_emitted means typedef definition
			 * was emitted, but it can be used only for "weak"
			 * references through pointer only, not for embedding
			 */
			if (!btf_dump_is_blacklisted(d, id)) {
				btf_dump_emit_typedef_def(d, id, t, 0);
				btf_dump_printf(d, ";\n\n");
			}
			tstate->fwd_emitted = 1;
			break;
		default:
			break;
		}

		return;
	}

	switch (kind) {
	case BTF_KIND_INT:
		/* Emit type alias definitions if necessary */
		btf_dump_emit_missing_aliases(d, id, t);

		tstate->emit_state = EMITTED;
		break;
	case BTF_KIND_ENUM:
		if (top_level_def) {
			btf_dump_emit_enum_def(d, id, t, 0);
			btf_dump_printf(d, ";\n\n");
		}
		tstate->emit_state = EMITTED;
		break;
	case BTF_KIND_PTR:
	case BTF_KIND_VOLATILE:
	case BTF_KIND_CONST:
	case BTF_KIND_RESTRICT:
		btf_dump_emit_type(d, t->type, cont_id);
		break;
	case BTF_KIND_ARRAY:
		btf_dump_emit_type(d, btf_array(t)->type, cont_id);
		break;
	case BTF_KIND_FWD:
		btf_dump_emit_fwd_def(d, id, t);
		btf_dump_printf(d, ";\n\n");
		tstate->emit_state = EMITTED;
		break;
	case BTF_KIND_TYPEDEF:
		tstate->emit_state = EMITTING;
		btf_dump_emit_type(d, t->type, id);
		/*
		 * typedef can server as both definition and forward
		 * declaration; at this stage someone depends on
		 * typedef as a forward declaration (refers to it
		 * through pointer), so unless we already did it,
		 * emit typedef as a forward declaration
		 */
		if (!tstate->fwd_emitted && !btf_dump_is_blacklisted(d, id)) {
			btf_dump_emit_typedef_def(d, id, t, 0);
			btf_dump_printf(d, ";\n\n");
		}
		tstate->emit_state = EMITTED;
		break;
	case BTF_KIND_STRUCT:
	case BTF_KIND_UNION:
		tstate->emit_state = EMITTING;
		/* if it's a top-level struct/union definition or struct/union
		 * is anonymous, then in C we'll be emitting all fields and
		 * their types (as opposed to just `struct X`), so we need to
		 * make sure that all types, referenced from struct/union
		 * members have necessary forward-declarations, where
		 * applicable
		 */
		if (top_level_def || t->name_off == 0) {
			const struct btf_member *m = btf_members(t);
			__u16 vlen = btf_vlen(t);
			int i, new_cont_id;

			new_cont_id = t->name_off == 0 ? cont_id : id;
			for (i = 0; i < vlen; i++, m++)
				btf_dump_emit_type(d, m->type, new_cont_id);
		} else if (!tstate->fwd_emitted && id != cont_id) {
			btf_dump_emit_struct_fwd(d, id, t);
			btf_dump_printf(d, ";\n\n");
			tstate->fwd_emitted = 1;
		}

		if (top_level_def) {
			btf_dump_emit_struct_def(d, id, t, 0);
			btf_dump_printf(d, ";\n\n");
			tstate->emit_state = EMITTED;
		} else {
			tstate->emit_state = NOT_EMITTED;
		}
		break;
	case BTF_KIND_FUNC_PROTO: {
		const struct btf_param *p = btf_params(t);
		__u16 vlen = btf_vlen(t);
		int i;

		btf_dump_emit_type(d, t->type, cont_id);
		for (i = 0; i < vlen; i++, p++)
			btf_dump_emit_type(d, p->type, cont_id);

		break;
	}
	default:
		break;
	}
}

static bool btf_is_struct_packed(const struct btf *btf, __u32 id,
				 const struct btf_type *t)
{
	const struct btf_member *m;
	int max_align = 1, align, i, bit_sz;
	__u16 vlen;

	m = btf_members(t);
	vlen = btf_vlen(t);
	/* all non-bitfield fields have to be naturally aligned */
	for (i = 0; i < vlen; i++, m++) {
		align = btf__align_of(btf, m->type);
		bit_sz = btf_member_bitfield_size(t, i);
		if (align && bit_sz == 0 && m->offset % (8 * align) != 0)
			return true;
		max_align = max(align, max_align);
	}
	/* size of a non-packed struct has to be a multiple of its alignment */
	if (t->size % max_align != 0)
		return true;
	/*
	 * if original struct was marked as packed, but its layout is
	 * naturally aligned, we'll detect that it's not packed
	 */
	return false;
}

static void btf_dump_emit_bit_padding(const struct btf_dump *d,
				      int cur_off, int next_off, int next_align,
				      bool in_bitfield, int lvl)
{
	const struct {
		const char *name;
		int bits;
	} pads[] = {
		{"long", d->ptr_sz * 8}, {"int", 32}, {"short", 16}, {"char", 8}
	};
	int new_off, pad_bits, bits, i;
	const char *pad_type;

	if (cur_off >= next_off)
		return; /* no gap */

	/* For filling out padding we want to take advantage of
	 * natural alignment rules to minimize unnecessary explicit
	 * padding. First, we find the largest type (among long, int,
	 * short, or char) that can be used to force naturally aligned
	 * boundary. Once determined, we'll use such type to fill in
	 * the remaining padding gap. In some cases we can rely on
	 * compiler filling some gaps, but sometimes we need to force
	 * alignment to close natural alignment with markers like
	 * `long: 0` (this is always the case for bitfields).  Note
	 * that even if struct itself has, let's say 4-byte alignment
	 * (i.e., it only uses up to int-aligned types), using `long:
	 * X;` explicit padding doesn't actually change struct's
	 * overall alignment requirements, but compiler does take into
	 * account that type's (long, in this example) natural
	 * alignment requirements when adding implicit padding. We use
	 * this fact heavily and don't worry about ruining correct
	 * struct alignment requirement.
	 */
	for (i = 0; i < ARRAY_SIZE(pads); i++) {
		pad_bits = pads[i].bits;
		pad_type = pads[i].name;

		new_off = roundup(cur_off, pad_bits);
		if (new_off <= next_off)
			break;
	}

	if (new_off > cur_off && new_off <= next_off) {
		/* We need explicit `<type>: 0` aligning mark if next
		 * field is right on alignment offset and its
		 * alignment requirement is less strict than <type>'s
		 * alignment (so compiler won't naturally align to the
		 * offset we expect), or if subsequent `<type>: X`,
		 * will actually completely fit in the remaining hole,
		 * making compiler basically ignore `<type>: X`
		 * completely.
		 */
		if (in_bitfield ||
		    (new_off == next_off && roundup(cur_off, next_align * 8) != new_off) ||
		    (new_off != next_off && next_off - new_off <= new_off - cur_off))
			/* but for bitfields we'll emit explicit bit count */
			btf_dump_printf(d, "\n%s%s: %d;", pfx(lvl), pad_type,
					in_bitfield ? new_off - cur_off : 0);
		cur_off = new_off;
	}

	/* Now we know we start at naturally aligned offset for a chosen
	 * padding type (long, int, short, or char), and so the rest is just
	 * a straightforward filling of remaining padding gap with full
	 * `<type>: sizeof(<type>);` markers, except for the last one, which
	 * might need smaller than sizeof(<type>) padding.
	 */
	while (cur_off != next_off) {
		bits = min(next_off - cur_off, pad_bits);
		if (bits == pad_bits) {
			btf_dump_printf(d, "\n%s%s: %d;", pfx(lvl), pad_type, pad_bits);
			cur_off += bits;
			continue;
		}
		/* For the remainder padding that doesn't cover entire
		 * pad_type bit length, we pick the smallest necessary type.
		 * This is pure aesthetics, we could have just used `long`,
		 * but having smallest necessary one communicates better the
		 * scale of the padding gap.
		 */
		for (i = ARRAY_SIZE(pads) - 1; i >= 0; i--) {
			pad_type = pads[i].name;
			pad_bits = pads[i].bits;
			if (pad_bits < bits)
				continue;

			btf_dump_printf(d, "\n%s%s: %d;", pfx(lvl), pad_type, bits);
			cur_off += bits;
			break;
		}
	}
}

static void btf_dump_emit_struct_fwd(struct btf_dump *d, __u32 id,
				     const struct btf_type *t)
{
	btf_dump_printf(d, "%s %s",
			btf_is_struct(t) ? "struct" : "union",
			btf_dump_type_name(d, id));
}

static void btf_dump_emit_struct_def(struct btf_dump *d,
				     __u32 id,
				     const struct btf_type *t,
				     int lvl)
{
	const struct btf_member *m = btf_members(t);
	bool is_struct = btf_is_struct(t);
	bool packed, prev_bitfield = false;
	int align, i, off = 0;
	__u16 vlen = btf_vlen(t);

	align = btf__align_of(d->btf, id);
	packed = is_struct ? btf_is_struct_packed(d->btf, id, t) : 0;

	btf_dump_printf(d, "%s%s%s {",
			is_struct ? "struct" : "union",
			t->name_off ? " " : "",
			btf_dump_type_name(d, id));

	for (i = 0; i < vlen; i++, m++) {
		const char *fname;
		int m_off, m_sz, m_align;
		bool in_bitfield;

		fname = btf_name_of(d, m->name_off);
		m_sz = btf_member_bitfield_size(t, i);
		m_off = btf_member_bit_offset(t, i);
		m_align = packed ? 1 : btf__align_of(d->btf, m->type);

		in_bitfield = prev_bitfield && m_sz != 0;

		btf_dump_emit_bit_padding(d, off, m_off, m_align, in_bitfield, lvl + 1);
		btf_dump_printf(d, "\n%s", pfx(lvl + 1));
		btf_dump_emit_type_decl(d, m->type, fname, lvl + 1);

		if (m_sz) {
			btf_dump_printf(d, ": %d", m_sz);
			off = m_off + m_sz;
			prev_bitfield = true;
		} else {
			m_sz = max((__s64)0, btf__resolve_size(d->btf, m->type));
			off = m_off + m_sz * 8;
			prev_bitfield = false;
		}

		btf_dump_printf(d, ";");
	}

	/* pad at the end, if necessary */
	if (is_struct)
		btf_dump_emit_bit_padding(d, off, t->size * 8, align, false, lvl + 1);

	/*
	 * Keep `struct empty {}` on a single line,
	 * only print newline when there are regular or padding fields.
	 */
	if (vlen || t->size) {
		btf_dump_printf(d, "\n");
		btf_dump_printf(d, "%s}", pfx(lvl));
	} else {
		btf_dump_printf(d, "}");
	}
	if (packed)
		btf_dump_printf(d, " __attribute__((packed))");
}

static const char *missing_base_types[][2] = {
	/*
	 * GCC emits typedefs to its internal __PolyX_t types when compiling Arm
	 * SIMD intrinsics. Alias them to standard base types.
	 */
	{ "__Poly8_t",		"unsigned char" },
	{ "__Poly16_t",		"unsigned short" },
	{ "__Poly64_t",		"unsigned long long" },
	{ "__Poly128_t",	"unsigned __int128" },
};

static void btf_dump_emit_missing_aliases(struct btf_dump *d, __u32 id,
					  const struct btf_type *t)
{
	const char *name = btf_dump_type_name(d, id);
	int i;

	for (i = 0; i < ARRAY_SIZE(missing_base_types); i++) {
		if (strcmp(name, missing_base_types[i][0]) == 0) {
			btf_dump_printf(d, "typedef %s %s;\n\n",
					missing_base_types[i][1], name);
			break;
		}
	}
}

static void btf_dump_emit_enum_fwd(struct btf_dump *d, __u32 id,
				   const struct btf_type *t)
{
	btf_dump_printf(d, "enum %s", btf_dump_type_name(d, id));
}

static void btf_dump_emit_enum_def(struct btf_dump *d, __u32 id,
				   const struct btf_type *t,
				   int lvl)
{
	const struct btf_enum *v = btf_enum(t);
	__u16 vlen = btf_vlen(t);
	const char *name;
	size_t dup_cnt;
	int i;

	btf_dump_printf(d, "enum%s%s",
			t->name_off ? " " : "",
			btf_dump_type_name(d, id));

	if (vlen) {
		btf_dump_printf(d, " {");
		for (i = 0; i < vlen; i++, v++) {
			name = btf_name_of(d, v->name_off);
			/* enumerators share namespace with typedef idents */
			dup_cnt = btf_dump_name_dups(d, d->ident_names, name);
			if (dup_cnt > 1) {
				btf_dump_printf(d, "\n%s%s___%zu = %u,",
						pfx(lvl + 1), name, dup_cnt,
						(__u32)v->val);
			} else {
				btf_dump_printf(d, "\n%s%s = %u,",
						pfx(lvl + 1), name,
						(__u32)v->val);
			}
		}
		btf_dump_printf(d, "\n%s}", pfx(lvl));
	}
}

static void btf_dump_emit_fwd_def(struct btf_dump *d, __u32 id,
				  const struct btf_type *t)
{
	const char *name = btf_dump_type_name(d, id);

	if (btf_kflag(t))
		btf_dump_printf(d, "union %s", name);
	else
		btf_dump_printf(d, "struct %s", name);
}

static void btf_dump_emit_typedef_def(struct btf_dump *d, __u32 id,
				     const struct btf_type *t, int lvl)
{
	const char *name = btf_dump_ident_name(d, id);

	/*
	 * Old GCC versions are emitting invalid typedef for __gnuc_va_list
	 * pointing to VOID. This generates warnings from btf_dump() and
	 * results in uncompilable header file, so we are fixing it up here
	 * with valid typedef into __builtin_va_list.
	 */
	if (t->type == 0 && strcmp(name, "__gnuc_va_list") == 0) {
		btf_dump_printf(d, "typedef __builtin_va_list __gnuc_va_list");
		return;
	}

	btf_dump_printf(d, "typedef ");
	btf_dump_emit_type_decl(d, t->type, name, lvl);
}

static int btf_dump_push_decl_stack_id(struct btf_dump *d, __u32 id)
{
	__u32 *new_stack;
	size_t new_cap;

	if (d->decl_stack_cnt >= d->decl_stack_cap) {
		new_cap = max(16, d->decl_stack_cap * 3 / 2);
		new_stack = libbpf_reallocarray(d->decl_stack, new_cap, sizeof(new_stack[0]));
		if (!new_stack)
			return -ENOMEM;
		d->decl_stack = new_stack;
		d->decl_stack_cap = new_cap;
	}

	d->decl_stack[d->decl_stack_cnt++] = id;

	return 0;
}

/*
 * Emit type declaration (e.g., field type declaration in a struct or argument
 * declaration in function prototype) in correct C syntax.
 *
 * For most types it's trivial, but there are few quirky type declaration
 * cases worth mentioning:
 *   - function prototypes (especially nesting of function prototypes);
 *   - arrays;
 *   - const/volatile/restrict for pointers vs other types.
 *
 * For a good discussion of *PARSING* C syntax (as a human), see
 * Peter van der Linden's "Expert C Programming: Deep C Secrets",
 * Ch.3 "Unscrambling Declarations in C".
 *
 * It won't help with BTF to C conversion much, though, as it's an opposite
 * problem. So we came up with this algorithm in reverse to van der Linden's
 * parsing algorithm. It goes from structured BTF representation of type
 * declaration to a valid compilable C syntax.
 *
 * For instance, consider this C typedef:
 *	typedef const int * const * arr[10] arr_t;
 * It will be represented in BTF with this chain of BTF types:
 *	[typedef] -> [array] -> [ptr] -> [const] -> [ptr] -> [const] -> [int]
 *
 * Notice how [const] modifier always goes before type it modifies in BTF type
 * graph, but in C syntax, const/volatile/restrict modifiers are written to
 * the right of pointers, but to the left of other types. There are also other
 * quirks, like function pointers, arrays of them, functions returning other
 * functions, etc.
 *
 * We handle that by pushing all the types to a stack, until we hit "terminal"
 * type (int/enum/struct/union/fwd). Then depending on the kind of a type on
 * top of a stack, modifiers are handled differently. Array/function pointers
 * have also wildly different syntax and how nesting of them are done. See
 * code for authoritative definition.
 *
 * To avoid allocating new stack for each independent chain of BTF types, we
 * share one bigger stack, with each chain working only on its own local view
 * of a stack frame. Some care is required to "pop" stack frames after
 * processing type declaration chain.
 */
int btf_dump__emit_type_decl(struct btf_dump *d, __u32 id,
			     const struct btf_dump_emit_type_decl_opts *opts)
{
	const char *fname;
	int lvl, err;

	if (!OPTS_VALID(opts, btf_dump_emit_type_decl_opts))
		return -EINVAL;

	err = btf_dump_resize(d);
	if (err)
		return -EINVAL;

	fname = OPTS_GET(opts, field_name, "");
	lvl = OPTS_GET(opts, indent_level, 0);
	d->strip_mods = OPTS_GET(opts, strip_mods, false);
	btf_dump_emit_type_decl(d, id, fname, lvl);
	d->strip_mods = false;
	return 0;
}

static void btf_dump_emit_type_decl(struct btf_dump *d, __u32 id,
				    const char *fname, int lvl)
{
	struct id_stack decl_stack;
	const struct btf_type *t;
	int err, stack_start;

	stack_start = d->decl_stack_cnt;
	for (;;) {
		t = btf__type_by_id(d->btf, id);
		if (d->strip_mods && btf_is_mod(t))
			goto skip_mod;

		err = btf_dump_push_decl_stack_id(d, id);
		if (err < 0) {
			/*
			 * if we don't have enough memory for entire type decl
			 * chain, restore stack, emit warning, and try to
			 * proceed nevertheless
			 */
			pr_warn("not enough memory for decl stack:%d", err);
			d->decl_stack_cnt = stack_start;
			return;
		}
skip_mod:
		/* VOID */
		if (id == 0)
			break;

		switch (btf_kind(t)) {
		case BTF_KIND_PTR:
		case BTF_KIND_VOLATILE:
		case BTF_KIND_CONST:
		case BTF_KIND_RESTRICT:
		case BTF_KIND_FUNC_PROTO:
			id = t->type;
			break;
		case BTF_KIND_ARRAY:
			id = btf_array(t)->type;
			break;
		case BTF_KIND_INT:
		case BTF_KIND_ENUM:
		case BTF_KIND_FWD:
		case BTF_KIND_STRUCT:
		case BTF_KIND_UNION:
		case BTF_KIND_TYPEDEF:
			goto done;
		default:
			pr_warn("unexpected type in decl chain, kind:%u, id:[%u]\n",
				btf_kind(t), id);
			goto done;
		}
	}
done:
	/*
	 * We might be inside a chain of declarations (e.g., array of function
	 * pointers returning anonymous (so inlined) structs, having another
	 * array field). Each of those needs its own "stack frame" to handle
	 * emitting of declarations. Those stack frames are non-overlapping
	 * portions of shared btf_dump->decl_stack. To make it a bit nicer to
	 * handle this set of nested stacks, we create a view corresponding to
	 * our own "stack frame" and work with it as an independent stack.
	 * We'll need to clean up after emit_type_chain() returns, though.
	 */
	decl_stack.ids = d->decl_stack + stack_start;
	decl_stack.cnt = d->decl_stack_cnt - stack_start;
	btf_dump_emit_type_chain(d, &decl_stack, fname, lvl);
	/*
	 * emit_type_chain() guarantees that it will pop its entire decl_stack
	 * frame before returning. But it works with a read-only view into
	 * decl_stack, so it doesn't actually pop anything from the
	 * perspective of shared btf_dump->decl_stack, per se. We need to
	 * reset decl_stack state to how it was before us to avoid it growing
	 * all the time.
	 */
	d->decl_stack_cnt = stack_start;
}

static void btf_dump_emit_mods(struct btf_dump *d, struct id_stack *decl_stack)
{
	const struct btf_type *t;
	__u32 id;

	while (decl_stack->cnt) {
		id = decl_stack->ids[decl_stack->cnt - 1];
		t = btf__type_by_id(d->btf, id);

		switch (btf_kind(t)) {
		case BTF_KIND_VOLATILE:
			btf_dump_printf(d, "volatile ");
			break;
		case BTF_KIND_CONST:
			btf_dump_printf(d, "const ");
			break;
		case BTF_KIND_RESTRICT:
			btf_dump_printf(d, "restrict ");
			break;
		default:
			return;
		}
		decl_stack->cnt--;
	}
}

static void btf_dump_drop_mods(struct btf_dump *d, struct id_stack *decl_stack)
{
	const struct btf_type *t;
	__u32 id;

	while (decl_stack->cnt) {
		id = decl_stack->ids[decl_stack->cnt - 1];
		t = btf__type_by_id(d->btf, id);
		if (!btf_is_mod(t))
			return;
		decl_stack->cnt--;
	}
}

static void btf_dump_emit_name(const struct btf_dump *d,
			       const char *name, bool last_was_ptr)
{
	bool separate = name[0] && !last_was_ptr;

	btf_dump_printf(d, "%s%s", separate ? " " : "", name);
}

static void btf_dump_emit_type_chain(struct btf_dump *d,
				     struct id_stack *decls,
				     const char *fname, int lvl)
{
	/*
	 * last_was_ptr is used to determine if we need to separate pointer
	 * asterisk (*) from previous part of type signature with space, so
	 * that we get `int ***`, instead of `int * * *`. We default to true
	 * for cases where we have single pointer in a chain. E.g., in ptr ->
	 * func_proto case. func_proto will start a new emit_type_chain call
	 * with just ptr, which should be emitted as (*) or (*<fname>), so we
	 * don't want to prepend space for that last pointer.
	 */
	bool last_was_ptr = true;
	const struct btf_type *t;
	const char *name;
	__u16 kind;
	__u32 id;

	while (decls->cnt) {
		id = decls->ids[--decls->cnt];
		if (id == 0) {
			/* VOID is a special snowflake */
			btf_dump_emit_mods(d, decls);
			btf_dump_printf(d, "void");
			last_was_ptr = false;
			continue;
		}

		t = btf__type_by_id(d->btf, id);
		kind = btf_kind(t);

		switch (kind) {
		case BTF_KIND_INT:
			btf_dump_emit_mods(d, decls);
			name = btf_name_of(d, t->name_off);
			btf_dump_printf(d, "%s", name);
			break;
		case BTF_KIND_STRUCT:
		case BTF_KIND_UNION:
			btf_dump_emit_mods(d, decls);
			/* inline anonymous struct/union */
			if (t->name_off == 0)
				btf_dump_emit_struct_def(d, id, t, lvl);
			else
				btf_dump_emit_struct_fwd(d, id, t);
			break;
		case BTF_KIND_ENUM:
			btf_dump_emit_mods(d, decls);
			/* inline anonymous enum */
			if (t->name_off == 0)
				btf_dump_emit_enum_def(d, id, t, lvl);
			else
				btf_dump_emit_enum_fwd(d, id, t);
			break;
		case BTF_KIND_FWD:
			btf_dump_emit_mods(d, decls);
			btf_dump_emit_fwd_def(d, id, t);
			break;
		case BTF_KIND_TYPEDEF:
			btf_dump_emit_mods(d, decls);
			btf_dump_printf(d, "%s", btf_dump_ident_name(d, id));
			break;
		case BTF_KIND_PTR:
			btf_dump_printf(d, "%s", last_was_ptr ? "*" : " *");
			break;
		case BTF_KIND_VOLATILE:
			btf_dump_printf(d, " volatile");
			break;
		case BTF_KIND_CONST:
			btf_dump_printf(d, " const");
			break;
		case BTF_KIND_RESTRICT:
			btf_dump_printf(d, " restrict");
			break;
		case BTF_KIND_ARRAY: {
			const struct btf_array *a = btf_array(t);
			const struct btf_type *next_t;
			__u32 next_id;
			bool multidim;
			/*
			 * GCC has a bug
			 * (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=8354)
			 * which causes it to emit extra const/volatile
			 * modifiers for an array, if array's element type has
			 * const/volatile modifiers. Clang doesn't do that.
			 * In general, it doesn't seem very meaningful to have
			 * a const/volatile modifier for array, so we are
			 * going to silently skip them here.
			 */
			btf_dump_drop_mods(d, decls);

			if (decls->cnt == 0) {
				btf_dump_emit_name(d, fname, last_was_ptr);
				btf_dump_printf(d, "[%u]", a->nelems);
				return;
			}

			next_id = decls->ids[decls->cnt - 1];
			next_t = btf__type_by_id(d->btf, next_id);
			multidim = btf_is_array(next_t);
			/* we need space if we have named non-pointer */
			if (fname[0] && !last_was_ptr)
				btf_dump_printf(d, " ");
			/* no parentheses for multi-dimensional array */
			if (!multidim)
				btf_dump_printf(d, "(");
			btf_dump_emit_type_chain(d, decls, fname, lvl);
			if (!multidim)
				btf_dump_printf(d, ")");
			btf_dump_printf(d, "[%u]", a->nelems);
			return;
		}
		case BTF_KIND_FUNC_PROTO: {
			const struct btf_param *p = btf_params(t);
			__u16 vlen = btf_vlen(t);
			int i;

			/*
			 * GCC emits extra volatile qualifier for
			 * __attribute__((noreturn)) function pointers. Clang
			 * doesn't do it. It's a GCC quirk for backwards
			 * compatibility with code written for GCC <2.5. So,
			 * similarly to extra qualifiers for array, just drop
			 * them, instead of handling them.
			 */
			btf_dump_drop_mods(d, decls);
			if (decls->cnt) {
				btf_dump_printf(d, " (");
				btf_dump_emit_type_chain(d, decls, fname, lvl);
				btf_dump_printf(d, ")");
			} else {
				btf_dump_emit_name(d, fname, last_was_ptr);
			}
			btf_dump_printf(d, "(");
			/*
			 * Clang for BPF target generates func_proto with no
			 * args as a func_proto with a single void arg (e.g.,
			 * `int (*f)(void)` vs just `int (*f)()`). We are
			 * going to pretend there are no args for such case.
			 */
			if (vlen == 1 && p->type == 0) {
				btf_dump_printf(d, ")");
				return;
			}

			for (i = 0; i < vlen; i++, p++) {
				if (i > 0)
					btf_dump_printf(d, ", ");

				/* last arg of type void is vararg */
				if (i == vlen - 1 && p->type == 0) {
					btf_dump_printf(d, "...");
					break;
				}

				name = btf_name_of(d, p->name_off);
				btf_dump_emit_type_decl(d, p->type, name, lvl);
			}

			btf_dump_printf(d, ")");
			return;
		}
		default:
			pr_warn("unexpected type in decl chain, kind:%u, id:[%u]\n",
				kind, id);
			return;
		}

		last_was_ptr = kind == BTF_KIND_PTR;
	}

	btf_dump_emit_name(d, fname, last_was_ptr);
}

/* return number of duplicates (occurrences) of a given name */
static size_t btf_dump_name_dups(struct btf_dump *d, struct hashmap *name_map,
				 const char *orig_name)
{
	char *old_name, *new_name;
	size_t dup_cnt = 0;
	int err;

	new_name = strdup(orig_name);
	if (!new_name)
		return 1;

	hashmap__find(name_map, orig_name, (void **)&dup_cnt);
	dup_cnt++;

	err = hashmap__set(name_map, new_name, (void *)dup_cnt,
			   (const void **)&old_name, NULL);
	if (err)
		free(new_name);

	free(old_name);

	return dup_cnt;
}

static const char *btf_dump_resolve_name(struct btf_dump *d, __u32 id,
					 struct hashmap *name_map)
{
	struct btf_dump_type_aux_state *s = &d->type_states[id];
	const struct btf_type *t = btf__type_by_id(d->btf, id);
	const char *orig_name = btf_name_of(d, t->name_off);
	const char **cached_name = &d->cached_names[id];
	size_t dup_cnt;

	if (t->name_off == 0)
		return "";

	if (s->name_resolved)
		return *cached_name ? *cached_name : orig_name;

	if (btf_is_fwd(t) || (btf_is_enum(t) && btf_vlen(t) == 0)) {
		s->name_resolved = 1;
		return orig_name;
	}

	dup_cnt = btf_dump_name_dups(d, name_map, orig_name);
	if (dup_cnt > 1) {
		const size_t max_len = 256;
		char new_name[max_len];

		snprintf(new_name, max_len, "%s___%zu", orig_name, dup_cnt);
		*cached_name = strdup(new_name);
	}

	s->name_resolved = 1;
	return *cached_name ? *cached_name : orig_name;
}

static const char *btf_dump_type_name(struct btf_dump *d, __u32 id)
{
	return btf_dump_resolve_name(d, id, d->type_names);
}

static const char *btf_dump_ident_name(struct btf_dump *d, __u32 id)
{
	return btf_dump_resolve_name(d, id, d->ident_names);
}