File: dwarf.go

package info (click to toggle)
golang-1.12 1.12.7-3
  • links: PTS, VCS
  • area: main
  • in suites: bullseye, experimental, sid
  • size: 113,080 kB
  • sloc: asm: 97,488; ansic: 8,245; perl: 2,243; sh: 1,895; xml: 623; python: 349; makefile: 127; cpp: 22; f90: 8; awk: 7
file content (2133 lines) | stat: -rw-r--r-- 69,320 bytes parent folder | download | duplicates (7)
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
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// TODO/NICETOHAVE:
//   - eliminate DW_CLS_ if not used
//   - package info in compilation units
//   - assign types to their packages
//   - gdb uses c syntax, meaning clumsy quoting is needed for go identifiers. eg
//     ptype struct '[]uint8' and qualifiers need to be quoted away
//   - file:line info for variables
//   - make strings a typedef so prettyprinters can see the underlying string type

package ld

import (
	"cmd/internal/dwarf"
	"cmd/internal/obj"
	"cmd/internal/objabi"
	"cmd/internal/sys"
	"cmd/link/internal/sym"
	"fmt"
	"log"
	"sort"
	"strings"
)

type dwctxt struct {
	linkctxt *Link
}

func (c dwctxt) PtrSize() int {
	return c.linkctxt.Arch.PtrSize
}
func (c dwctxt) AddInt(s dwarf.Sym, size int, i int64) {
	ls := s.(*sym.Symbol)
	ls.AddUintXX(c.linkctxt.Arch, uint64(i), size)
}
func (c dwctxt) AddBytes(s dwarf.Sym, b []byte) {
	ls := s.(*sym.Symbol)
	ls.AddBytes(b)
}
func (c dwctxt) AddString(s dwarf.Sym, v string) {
	Addstring(s.(*sym.Symbol), v)
}

func (c dwctxt) AddAddress(s dwarf.Sym, data interface{}, value int64) {
	if value != 0 {
		value -= (data.(*sym.Symbol)).Value
	}
	s.(*sym.Symbol).AddAddrPlus(c.linkctxt.Arch, data.(*sym.Symbol), value)
}

func (c dwctxt) AddSectionOffset(s dwarf.Sym, size int, t interface{}, ofs int64) {
	ls := s.(*sym.Symbol)
	switch size {
	default:
		Errorf(ls, "invalid size %d in adddwarfref\n", size)
		fallthrough
	case c.linkctxt.Arch.PtrSize:
		ls.AddAddr(c.linkctxt.Arch, t.(*sym.Symbol))
	case 4:
		ls.AddAddrPlus4(t.(*sym.Symbol), 0)
	}
	r := &ls.R[len(ls.R)-1]
	r.Type = objabi.R_ADDROFF
	r.Add = ofs
}

func (c dwctxt) AddDWARFAddrSectionOffset(s dwarf.Sym, t interface{}, ofs int64) {
	size := 4
	if isDwarf64(c.linkctxt) {
		size = 8
	}

	c.AddSectionOffset(s, size, t, ofs)
	ls := s.(*sym.Symbol)
	ls.R[len(ls.R)-1].Type = objabi.R_DWARFSECREF
}

func (c dwctxt) Logf(format string, args ...interface{}) {
	c.linkctxt.Logf(format, args...)
}

// At the moment these interfaces are only used in the compiler.

func (c dwctxt) AddFileRef(s dwarf.Sym, f interface{}) {
	panic("should be used only in the compiler")
}

func (c dwctxt) CurrentOffset(s dwarf.Sym) int64 {
	panic("should be used only in the compiler")
}

func (c dwctxt) RecordDclReference(s dwarf.Sym, t dwarf.Sym, dclIdx int, inlIndex int) {
	panic("should be used only in the compiler")
}

func (c dwctxt) RecordChildDieOffsets(s dwarf.Sym, vars []*dwarf.Var, offsets []int32) {
	panic("should be used only in the compiler")
}

func isDwarf64(ctxt *Link) bool {
	return ctxt.HeadType == objabi.Haix
}

var gdbscript string

var dwarfp []*sym.Symbol

func writeabbrev(ctxt *Link) *sym.Symbol {
	s := ctxt.Syms.Lookup(".debug_abbrev", 0)
	s.Type = sym.SDWARFSECT
	s.AddBytes(dwarf.GetAbbrev())
	return s
}

var dwtypes dwarf.DWDie

func newattr(die *dwarf.DWDie, attr uint16, cls int, value int64, data interface{}) *dwarf.DWAttr {
	a := new(dwarf.DWAttr)
	a.Link = die.Attr
	die.Attr = a
	a.Atr = attr
	a.Cls = uint8(cls)
	a.Value = value
	a.Data = data
	return a
}

// Each DIE (except the root ones) has at least 1 attribute: its
// name. getattr moves the desired one to the front so
// frequently searched ones are found faster.
func getattr(die *dwarf.DWDie, attr uint16) *dwarf.DWAttr {
	if die.Attr.Atr == attr {
		return die.Attr
	}

	a := die.Attr
	b := a.Link
	for b != nil {
		if b.Atr == attr {
			a.Link = b.Link
			b.Link = die.Attr
			die.Attr = b
			return b
		}

		a = b
		b = b.Link
	}

	return nil
}

// Every DIE manufactured by the linker has at least an AT_name
// attribute (but it will only be written out if it is listed in the abbrev).
// The compiler does create nameless DWARF DIEs (ex: concrete subprogram
// instance).
func newdie(ctxt *Link, parent *dwarf.DWDie, abbrev int, name string, version int) *dwarf.DWDie {
	die := new(dwarf.DWDie)
	die.Abbrev = abbrev
	die.Link = parent.Child
	parent.Child = die

	newattr(die, dwarf.DW_AT_name, dwarf.DW_CLS_STRING, int64(len(name)), name)

	if name != "" && (abbrev <= dwarf.DW_ABRV_VARIABLE || abbrev >= dwarf.DW_ABRV_NULLTYPE) {
		if abbrev != dwarf.DW_ABRV_VARIABLE || version == 0 {
			if abbrev == dwarf.DW_ABRV_COMPUNIT {
				// Avoid collisions with "real" symbol names.
				name = ".pkg." + name
			}
			s := ctxt.Syms.Lookup(dwarf.InfoPrefix+name, version)
			s.Attr |= sym.AttrNotInSymbolTable
			s.Type = sym.SDWARFINFO
			die.Sym = s
		}
	}

	return die
}

func walktypedef(die *dwarf.DWDie) *dwarf.DWDie {
	if die == nil {
		return nil
	}
	// Resolve typedef if present.
	if die.Abbrev == dwarf.DW_ABRV_TYPEDECL {
		for attr := die.Attr; attr != nil; attr = attr.Link {
			if attr.Atr == dwarf.DW_AT_type && attr.Cls == dwarf.DW_CLS_REFERENCE && attr.Data != nil {
				return attr.Data.(*dwarf.DWDie)
			}
		}
	}

	return die
}

func walksymtypedef(ctxt *Link, s *sym.Symbol) *sym.Symbol {
	if t := ctxt.Syms.ROLookup(s.Name+"..def", int(s.Version)); t != nil {
		return t
	}
	return s
}

// Find child by AT_name using hashtable if available or linear scan
// if not.
func findchild(die *dwarf.DWDie, name string) *dwarf.DWDie {
	var prev *dwarf.DWDie
	for ; die != prev; prev, die = die, walktypedef(die) {
		for a := die.Child; a != nil; a = a.Link {
			if name == getattr(a, dwarf.DW_AT_name).Data {
				return a
			}
		}
		continue
	}
	return nil
}

// Used to avoid string allocation when looking up dwarf symbols
var prefixBuf = []byte(dwarf.InfoPrefix)

func find(ctxt *Link, name string) *sym.Symbol {
	n := append(prefixBuf, name...)
	// The string allocation below is optimized away because it is only used in a map lookup.
	s := ctxt.Syms.ROLookup(string(n), 0)
	prefixBuf = n[:len(dwarf.InfoPrefix)]
	if s != nil && s.Type == sym.SDWARFINFO {
		return s
	}
	return nil
}

func mustFind(ctxt *Link, name string) *sym.Symbol {
	r := find(ctxt, name)
	if r == nil {
		Exitf("dwarf find: cannot find %s", name)
	}
	return r
}

func adddwarfref(ctxt *Link, s *sym.Symbol, t *sym.Symbol, size int) int64 {
	var result int64
	switch size {
	default:
		Errorf(s, "invalid size %d in adddwarfref\n", size)
		fallthrough
	case ctxt.Arch.PtrSize:
		result = s.AddAddr(ctxt.Arch, t)
	case 4:
		result = s.AddAddrPlus4(t, 0)
	}
	r := &s.R[len(s.R)-1]
	r.Type = objabi.R_DWARFSECREF
	return result
}

func newrefattr(die *dwarf.DWDie, attr uint16, ref *sym.Symbol) *dwarf.DWAttr {
	if ref == nil {
		return nil
	}
	return newattr(die, attr, dwarf.DW_CLS_REFERENCE, 0, ref)
}

func putdies(linkctxt *Link, ctxt dwarf.Context, syms []*sym.Symbol, die *dwarf.DWDie) []*sym.Symbol {
	for ; die != nil; die = die.Link {
		syms = putdie(linkctxt, ctxt, syms, die)
	}
	syms[len(syms)-1].AddUint8(0)

	return syms
}

func dtolsym(s dwarf.Sym) *sym.Symbol {
	if s == nil {
		return nil
	}
	return s.(*sym.Symbol)
}

func putdie(linkctxt *Link, ctxt dwarf.Context, syms []*sym.Symbol, die *dwarf.DWDie) []*sym.Symbol {
	s := dtolsym(die.Sym)
	if s == nil {
		s = syms[len(syms)-1]
	} else {
		if s.Attr.OnList() {
			log.Fatalf("symbol %s listed multiple times", s.Name)
		}
		s.Attr |= sym.AttrOnList
		syms = append(syms, s)
	}
	dwarf.Uleb128put(ctxt, s, int64(die.Abbrev))
	dwarf.PutAttrs(ctxt, s, die.Abbrev, die.Attr)
	if dwarf.HasChildren(die) {
		return putdies(linkctxt, ctxt, syms, die.Child)
	}
	return syms
}

func reverselist(list **dwarf.DWDie) {
	curr := *list
	var prev *dwarf.DWDie
	for curr != nil {
		next := curr.Link
		curr.Link = prev
		prev = curr
		curr = next
	}

	*list = prev
}

func reversetree(list **dwarf.DWDie) {
	reverselist(list)
	for die := *list; die != nil; die = die.Link {
		if dwarf.HasChildren(die) {
			reversetree(&die.Child)
		}
	}
}

func newmemberoffsetattr(die *dwarf.DWDie, offs int32) {
	newattr(die, dwarf.DW_AT_data_member_location, dwarf.DW_CLS_CONSTANT, int64(offs), nil)
}

// GDB doesn't like FORM_addr for AT_location, so emit a
// location expression that evals to a const.
func newabslocexprattr(die *dwarf.DWDie, addr int64, sym *sym.Symbol) {
	newattr(die, dwarf.DW_AT_location, dwarf.DW_CLS_ADDRESS, addr, sym)
	// below
}

// Lookup predefined types
func lookupOrDiag(ctxt *Link, n string) *sym.Symbol {
	s := ctxt.Syms.ROLookup(n, 0)
	if s == nil || s.Size == 0 {
		Exitf("dwarf: missing type: %s", n)
	}

	return s
}

// dwarfFuncSym looks up a DWARF metadata symbol for function symbol s.
// If the symbol does not exist, it creates it if create is true,
// or returns nil otherwise.
func dwarfFuncSym(ctxt *Link, s *sym.Symbol, meta string, create bool) *sym.Symbol {
	// All function ABIs use symbol version 0 for the DWARF data.
	//
	// TODO(austin): It may be useful to have DWARF info for ABI
	// wrappers, in which case we may want these versions to
	// align. Better yet, replace these name lookups with a
	// general way to attach metadata to a symbol.
	ver := 0
	if s.IsFileLocal() {
		ver = int(s.Version)
	}
	if create {
		return ctxt.Syms.Lookup(meta+s.Name, ver)
	}
	return ctxt.Syms.ROLookup(meta+s.Name, ver)
}

func dotypedef(ctxt *Link, parent *dwarf.DWDie, name string, def *dwarf.DWDie) *dwarf.DWDie {
	// Only emit typedefs for real names.
	if strings.HasPrefix(name, "map[") {
		return nil
	}
	if strings.HasPrefix(name, "struct {") {
		return nil
	}
	if strings.HasPrefix(name, "chan ") {
		return nil
	}
	if name[0] == '[' || name[0] == '*' {
		return nil
	}
	if def == nil {
		Errorf(nil, "dwarf: bad def in dotypedef")
	}

	s := ctxt.Syms.Lookup(dtolsym(def.Sym).Name+"..def", 0)
	s.Attr |= sym.AttrNotInSymbolTable
	s.Type = sym.SDWARFINFO
	def.Sym = s

	// The typedef entry must be created after the def,
	// so that future lookups will find the typedef instead
	// of the real definition. This hooks the typedef into any
	// circular definition loops, so that gdb can understand them.
	die := newdie(ctxt, parent, dwarf.DW_ABRV_TYPEDECL, name, 0)

	newrefattr(die, dwarf.DW_AT_type, s)

	return die
}

// Define gotype, for composite ones recurse into constituents.
func defgotype(ctxt *Link, gotype *sym.Symbol) *sym.Symbol {
	if gotype == nil {
		return mustFind(ctxt, "<unspecified>")
	}

	if !strings.HasPrefix(gotype.Name, "type.") {
		Errorf(gotype, "dwarf: type name doesn't start with \"type.\"")
		return mustFind(ctxt, "<unspecified>")
	}

	name := gotype.Name[5:] // could also decode from Type.string

	sdie := find(ctxt, name)

	if sdie != nil {
		return sdie
	}

	return newtype(ctxt, gotype).Sym.(*sym.Symbol)
}

func newtype(ctxt *Link, gotype *sym.Symbol) *dwarf.DWDie {
	name := gotype.Name[5:] // could also decode from Type.string
	kind := decodetypeKind(ctxt.Arch, gotype)
	bytesize := decodetypeSize(ctxt.Arch, gotype)

	var die, typedefdie *dwarf.DWDie
	switch kind {
	case objabi.KindBool:
		die = newdie(ctxt, &dwtypes, dwarf.DW_ABRV_BASETYPE, name, 0)
		newattr(die, dwarf.DW_AT_encoding, dwarf.DW_CLS_CONSTANT, dwarf.DW_ATE_boolean, 0)
		newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, bytesize, 0)

	case objabi.KindInt,
		objabi.KindInt8,
		objabi.KindInt16,
		objabi.KindInt32,
		objabi.KindInt64:
		die = newdie(ctxt, &dwtypes, dwarf.DW_ABRV_BASETYPE, name, 0)
		newattr(die, dwarf.DW_AT_encoding, dwarf.DW_CLS_CONSTANT, dwarf.DW_ATE_signed, 0)
		newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, bytesize, 0)

	case objabi.KindUint,
		objabi.KindUint8,
		objabi.KindUint16,
		objabi.KindUint32,
		objabi.KindUint64,
		objabi.KindUintptr:
		die = newdie(ctxt, &dwtypes, dwarf.DW_ABRV_BASETYPE, name, 0)
		newattr(die, dwarf.DW_AT_encoding, dwarf.DW_CLS_CONSTANT, dwarf.DW_ATE_unsigned, 0)
		newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, bytesize, 0)

	case objabi.KindFloat32,
		objabi.KindFloat64:
		die = newdie(ctxt, &dwtypes, dwarf.DW_ABRV_BASETYPE, name, 0)
		newattr(die, dwarf.DW_AT_encoding, dwarf.DW_CLS_CONSTANT, dwarf.DW_ATE_float, 0)
		newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, bytesize, 0)

	case objabi.KindComplex64,
		objabi.KindComplex128:
		die = newdie(ctxt, &dwtypes, dwarf.DW_ABRV_BASETYPE, name, 0)
		newattr(die, dwarf.DW_AT_encoding, dwarf.DW_CLS_CONSTANT, dwarf.DW_ATE_complex_float, 0)
		newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, bytesize, 0)

	case objabi.KindArray:
		die = newdie(ctxt, &dwtypes, dwarf.DW_ABRV_ARRAYTYPE, name, 0)
		typedefdie = dotypedef(ctxt, &dwtypes, name, die)
		newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, bytesize, 0)
		s := decodetypeArrayElem(ctxt.Arch, gotype)
		newrefattr(die, dwarf.DW_AT_type, defgotype(ctxt, s))
		fld := newdie(ctxt, die, dwarf.DW_ABRV_ARRAYRANGE, "range", 0)

		// use actual length not upper bound; correct for 0-length arrays.
		newattr(fld, dwarf.DW_AT_count, dwarf.DW_CLS_CONSTANT, decodetypeArrayLen(ctxt.Arch, gotype), 0)

		newrefattr(fld, dwarf.DW_AT_type, mustFind(ctxt, "uintptr"))

	case objabi.KindChan:
		die = newdie(ctxt, &dwtypes, dwarf.DW_ABRV_CHANTYPE, name, 0)
		s := decodetypeChanElem(ctxt.Arch, gotype)
		newrefattr(die, dwarf.DW_AT_go_elem, defgotype(ctxt, s))
		// Save elem type for synthesizechantypes. We could synthesize here
		// but that would change the order of DIEs we output.
		newrefattr(die, dwarf.DW_AT_type, s)

	case objabi.KindFunc:
		die = newdie(ctxt, &dwtypes, dwarf.DW_ABRV_FUNCTYPE, name, 0)
		newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, bytesize, 0)
		typedefdie = dotypedef(ctxt, &dwtypes, name, die)
		nfields := decodetypeFuncInCount(ctxt.Arch, gotype)
		for i := 0; i < nfields; i++ {
			s := decodetypeFuncInType(ctxt.Arch, gotype, i)
			fld := newdie(ctxt, die, dwarf.DW_ABRV_FUNCTYPEPARAM, s.Name[5:], 0)
			newrefattr(fld, dwarf.DW_AT_type, defgotype(ctxt, s))
		}

		if decodetypeFuncDotdotdot(ctxt.Arch, gotype) {
			newdie(ctxt, die, dwarf.DW_ABRV_DOTDOTDOT, "...", 0)
		}
		nfields = decodetypeFuncOutCount(ctxt.Arch, gotype)
		for i := 0; i < nfields; i++ {
			s := decodetypeFuncOutType(ctxt.Arch, gotype, i)
			fld := newdie(ctxt, die, dwarf.DW_ABRV_FUNCTYPEPARAM, s.Name[5:], 0)
			newrefattr(fld, dwarf.DW_AT_type, defptrto(ctxt, defgotype(ctxt, s)))
		}

	case objabi.KindInterface:
		die = newdie(ctxt, &dwtypes, dwarf.DW_ABRV_IFACETYPE, name, 0)
		typedefdie = dotypedef(ctxt, &dwtypes, name, die)
		nfields := int(decodetypeIfaceMethodCount(ctxt.Arch, gotype))
		var s *sym.Symbol
		if nfields == 0 {
			s = lookupOrDiag(ctxt, "type.runtime.eface")
		} else {
			s = lookupOrDiag(ctxt, "type.runtime.iface")
		}
		newrefattr(die, dwarf.DW_AT_type, defgotype(ctxt, s))

	case objabi.KindMap:
		die = newdie(ctxt, &dwtypes, dwarf.DW_ABRV_MAPTYPE, name, 0)
		s := decodetypeMapKey(ctxt.Arch, gotype)
		newrefattr(die, dwarf.DW_AT_go_key, defgotype(ctxt, s))
		s = decodetypeMapValue(ctxt.Arch, gotype)
		newrefattr(die, dwarf.DW_AT_go_elem, defgotype(ctxt, s))
		// Save gotype for use in synthesizemaptypes. We could synthesize here,
		// but that would change the order of the DIEs.
		newrefattr(die, dwarf.DW_AT_type, gotype)

	case objabi.KindPtr:
		die = newdie(ctxt, &dwtypes, dwarf.DW_ABRV_PTRTYPE, name, 0)
		typedefdie = dotypedef(ctxt, &dwtypes, name, die)
		s := decodetypePtrElem(ctxt.Arch, gotype)
		newrefattr(die, dwarf.DW_AT_type, defgotype(ctxt, s))

	case objabi.KindSlice:
		die = newdie(ctxt, &dwtypes, dwarf.DW_ABRV_SLICETYPE, name, 0)
		typedefdie = dotypedef(ctxt, &dwtypes, name, die)
		newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, bytesize, 0)
		s := decodetypeArrayElem(ctxt.Arch, gotype)
		elem := defgotype(ctxt, s)
		newrefattr(die, dwarf.DW_AT_go_elem, elem)

	case objabi.KindString:
		die = newdie(ctxt, &dwtypes, dwarf.DW_ABRV_STRINGTYPE, name, 0)
		newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, bytesize, 0)

	case objabi.KindStruct:
		die = newdie(ctxt, &dwtypes, dwarf.DW_ABRV_STRUCTTYPE, name, 0)
		typedefdie = dotypedef(ctxt, &dwtypes, name, die)
		newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, bytesize, 0)
		nfields := decodetypeStructFieldCount(ctxt.Arch, gotype)
		for i := 0; i < nfields; i++ {
			f := decodetypeStructFieldName(ctxt.Arch, gotype, i)
			s := decodetypeStructFieldType(ctxt.Arch, gotype, i)
			if f == "" {
				f = s.Name[5:] // skip "type."
			}
			fld := newdie(ctxt, die, dwarf.DW_ABRV_STRUCTFIELD, f, 0)
			newrefattr(fld, dwarf.DW_AT_type, defgotype(ctxt, s))
			offsetAnon := decodetypeStructFieldOffsAnon(ctxt.Arch, gotype, i)
			newmemberoffsetattr(fld, int32(offsetAnon>>1))
			if offsetAnon&1 != 0 { // is embedded field
				newattr(fld, dwarf.DW_AT_go_embedded_field, dwarf.DW_CLS_FLAG, 1, 0)
			}
		}

	case objabi.KindUnsafePointer:
		die = newdie(ctxt, &dwtypes, dwarf.DW_ABRV_BARE_PTRTYPE, name, 0)

	default:
		Errorf(gotype, "dwarf: definition of unknown kind %d", kind)
		die = newdie(ctxt, &dwtypes, dwarf.DW_ABRV_TYPEDECL, name, 0)
		newrefattr(die, dwarf.DW_AT_type, mustFind(ctxt, "<unspecified>"))
	}

	newattr(die, dwarf.DW_AT_go_kind, dwarf.DW_CLS_CONSTANT, int64(kind), 0)
	if gotype.Attr.Reachable() {
		newattr(die, dwarf.DW_AT_go_runtime_type, dwarf.DW_CLS_GO_TYPEREF, 0, gotype)
	}

	if _, ok := prototypedies[gotype.Name]; ok {
		prototypedies[gotype.Name] = die
	}

	if typedefdie != nil {
		return typedefdie
	}
	return die
}

func nameFromDIESym(dwtype *sym.Symbol) string {
	return strings.TrimSuffix(dwtype.Name[len(dwarf.InfoPrefix):], "..def")
}

// Find or construct *T given T.
func defptrto(ctxt *Link, dwtype *sym.Symbol) *sym.Symbol {
	ptrname := "*" + nameFromDIESym(dwtype)
	if die := find(ctxt, ptrname); die != nil {
		return die
	}

	pdie := newdie(ctxt, &dwtypes, dwarf.DW_ABRV_PTRTYPE, ptrname, 0)
	newrefattr(pdie, dwarf.DW_AT_type, dwtype)

	// The DWARF info synthesizes pointer types that don't exist at the
	// language level, like *hash<...> and *bucket<...>, and the data
	// pointers of slices. Link to the ones we can find.
	gotype := ctxt.Syms.ROLookup("type."+ptrname, 0)
	if gotype != nil && gotype.Attr.Reachable() {
		newattr(pdie, dwarf.DW_AT_go_runtime_type, dwarf.DW_CLS_GO_TYPEREF, 0, gotype)
	}
	return dtolsym(pdie.Sym)
}

// Copies src's children into dst. Copies attributes by value.
// DWAttr.data is copied as pointer only. If except is one of
// the top-level children, it will not be copied.
func copychildrenexcept(ctxt *Link, dst *dwarf.DWDie, src *dwarf.DWDie, except *dwarf.DWDie) {
	for src = src.Child; src != nil; src = src.Link {
		if src == except {
			continue
		}
		c := newdie(ctxt, dst, src.Abbrev, getattr(src, dwarf.DW_AT_name).Data.(string), 0)
		for a := src.Attr; a != nil; a = a.Link {
			newattr(c, a.Atr, int(a.Cls), a.Value, a.Data)
		}
		copychildrenexcept(ctxt, c, src, nil)
	}

	reverselist(&dst.Child)
}

func copychildren(ctxt *Link, dst *dwarf.DWDie, src *dwarf.DWDie) {
	copychildrenexcept(ctxt, dst, src, nil)
}

// Search children (assumed to have TAG_member) for the one named
// field and set its AT_type to dwtype
func substitutetype(structdie *dwarf.DWDie, field string, dwtype *sym.Symbol) {
	child := findchild(structdie, field)
	if child == nil {
		Exitf("dwarf substitutetype: %s does not have member %s",
			getattr(structdie, dwarf.DW_AT_name).Data, field)
		return
	}

	a := getattr(child, dwarf.DW_AT_type)
	if a != nil {
		a.Data = dwtype
	} else {
		newrefattr(child, dwarf.DW_AT_type, dwtype)
	}
}

func findprotodie(ctxt *Link, name string) *dwarf.DWDie {
	die, ok := prototypedies[name]
	if ok && die == nil {
		defgotype(ctxt, lookupOrDiag(ctxt, name))
		die = prototypedies[name]
	}
	return die
}

func synthesizestringtypes(ctxt *Link, die *dwarf.DWDie) {
	prototype := walktypedef(findprotodie(ctxt, "type.runtime.stringStructDWARF"))
	if prototype == nil {
		return
	}

	for ; die != nil; die = die.Link {
		if die.Abbrev != dwarf.DW_ABRV_STRINGTYPE {
			continue
		}
		copychildren(ctxt, die, prototype)
	}
}

func synthesizeslicetypes(ctxt *Link, die *dwarf.DWDie) {
	prototype := walktypedef(findprotodie(ctxt, "type.runtime.slice"))
	if prototype == nil {
		return
	}

	for ; die != nil; die = die.Link {
		if die.Abbrev != dwarf.DW_ABRV_SLICETYPE {
			continue
		}
		copychildren(ctxt, die, prototype)
		elem := getattr(die, dwarf.DW_AT_go_elem).Data.(*sym.Symbol)
		substitutetype(die, "array", defptrto(ctxt, elem))
	}
}

func mkinternaltypename(base string, arg1 string, arg2 string) string {
	if arg2 == "" {
		return fmt.Sprintf("%s<%s>", base, arg1)
	}
	return fmt.Sprintf("%s<%s,%s>", base, arg1, arg2)
}

// synthesizemaptypes is way too closely married to runtime/hashmap.c
const (
	MaxKeySize = 128
	MaxValSize = 128
	BucketSize = 8
)

func mkinternaltype(ctxt *Link, abbrev int, typename, keyname, valname string, f func(*dwarf.DWDie)) *sym.Symbol {
	name := mkinternaltypename(typename, keyname, valname)
	symname := dwarf.InfoPrefix + name
	s := ctxt.Syms.ROLookup(symname, 0)
	if s != nil && s.Type == sym.SDWARFINFO {
		return s
	}
	die := newdie(ctxt, &dwtypes, abbrev, name, 0)
	f(die)
	return dtolsym(die.Sym)
}

func synthesizemaptypes(ctxt *Link, die *dwarf.DWDie) {
	hash := walktypedef(findprotodie(ctxt, "type.runtime.hmap"))
	bucket := walktypedef(findprotodie(ctxt, "type.runtime.bmap"))

	if hash == nil {
		return
	}

	for ; die != nil; die = die.Link {
		if die.Abbrev != dwarf.DW_ABRV_MAPTYPE {
			continue
		}
		gotype := getattr(die, dwarf.DW_AT_type).Data.(*sym.Symbol)
		keytype := decodetypeMapKey(ctxt.Arch, gotype)
		valtype := decodetypeMapValue(ctxt.Arch, gotype)
		keysize, valsize := decodetypeSize(ctxt.Arch, keytype), decodetypeSize(ctxt.Arch, valtype)
		keytype, valtype = walksymtypedef(ctxt, defgotype(ctxt, keytype)), walksymtypedef(ctxt, defgotype(ctxt, valtype))

		// compute size info like hashmap.c does.
		indirectKey, indirectVal := false, false
		if keysize > MaxKeySize {
			keysize = int64(ctxt.Arch.PtrSize)
			indirectKey = true
		}
		if valsize > MaxValSize {
			valsize = int64(ctxt.Arch.PtrSize)
			indirectVal = true
		}

		// Construct type to represent an array of BucketSize keys
		keyname := nameFromDIESym(keytype)
		dwhks := mkinternaltype(ctxt, dwarf.DW_ABRV_ARRAYTYPE, "[]key", keyname, "", func(dwhk *dwarf.DWDie) {
			newattr(dwhk, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, BucketSize*keysize, 0)
			t := keytype
			if indirectKey {
				t = defptrto(ctxt, keytype)
			}
			newrefattr(dwhk, dwarf.DW_AT_type, t)
			fld := newdie(ctxt, dwhk, dwarf.DW_ABRV_ARRAYRANGE, "size", 0)
			newattr(fld, dwarf.DW_AT_count, dwarf.DW_CLS_CONSTANT, BucketSize, 0)
			newrefattr(fld, dwarf.DW_AT_type, mustFind(ctxt, "uintptr"))
		})

		// Construct type to represent an array of BucketSize values
		valname := nameFromDIESym(valtype)
		dwhvs := mkinternaltype(ctxt, dwarf.DW_ABRV_ARRAYTYPE, "[]val", valname, "", func(dwhv *dwarf.DWDie) {
			newattr(dwhv, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, BucketSize*valsize, 0)
			t := valtype
			if indirectVal {
				t = defptrto(ctxt, valtype)
			}
			newrefattr(dwhv, dwarf.DW_AT_type, t)
			fld := newdie(ctxt, dwhv, dwarf.DW_ABRV_ARRAYRANGE, "size", 0)
			newattr(fld, dwarf.DW_AT_count, dwarf.DW_CLS_CONSTANT, BucketSize, 0)
			newrefattr(fld, dwarf.DW_AT_type, mustFind(ctxt, "uintptr"))
		})

		// Construct bucket<K,V>
		dwhbs := mkinternaltype(ctxt, dwarf.DW_ABRV_STRUCTTYPE, "bucket", keyname, valname, func(dwhb *dwarf.DWDie) {
			// Copy over all fields except the field "data" from the generic
			// bucket. "data" will be replaced with keys/values below.
			copychildrenexcept(ctxt, dwhb, bucket, findchild(bucket, "data"))

			fld := newdie(ctxt, dwhb, dwarf.DW_ABRV_STRUCTFIELD, "keys", 0)
			newrefattr(fld, dwarf.DW_AT_type, dwhks)
			newmemberoffsetattr(fld, BucketSize)
			fld = newdie(ctxt, dwhb, dwarf.DW_ABRV_STRUCTFIELD, "values", 0)
			newrefattr(fld, dwarf.DW_AT_type, dwhvs)
			newmemberoffsetattr(fld, BucketSize+BucketSize*int32(keysize))
			fld = newdie(ctxt, dwhb, dwarf.DW_ABRV_STRUCTFIELD, "overflow", 0)
			newrefattr(fld, dwarf.DW_AT_type, defptrto(ctxt, dtolsym(dwhb.Sym)))
			newmemberoffsetattr(fld, BucketSize+BucketSize*(int32(keysize)+int32(valsize)))
			if ctxt.Arch.RegSize > ctxt.Arch.PtrSize {
				fld = newdie(ctxt, dwhb, dwarf.DW_ABRV_STRUCTFIELD, "pad", 0)
				newrefattr(fld, dwarf.DW_AT_type, mustFind(ctxt, "uintptr"))
				newmemberoffsetattr(fld, BucketSize+BucketSize*(int32(keysize)+int32(valsize))+int32(ctxt.Arch.PtrSize))
			}

			newattr(dwhb, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, BucketSize+BucketSize*keysize+BucketSize*valsize+int64(ctxt.Arch.RegSize), 0)
		})

		// Construct hash<K,V>
		dwhs := mkinternaltype(ctxt, dwarf.DW_ABRV_STRUCTTYPE, "hash", keyname, valname, func(dwh *dwarf.DWDie) {
			copychildren(ctxt, dwh, hash)
			substitutetype(dwh, "buckets", defptrto(ctxt, dwhbs))
			substitutetype(dwh, "oldbuckets", defptrto(ctxt, dwhbs))
			newattr(dwh, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, getattr(hash, dwarf.DW_AT_byte_size).Value, nil)
		})

		// make map type a pointer to hash<K,V>
		newrefattr(die, dwarf.DW_AT_type, defptrto(ctxt, dwhs))
	}
}

func synthesizechantypes(ctxt *Link, die *dwarf.DWDie) {
	sudog := walktypedef(findprotodie(ctxt, "type.runtime.sudog"))
	waitq := walktypedef(findprotodie(ctxt, "type.runtime.waitq"))
	hchan := walktypedef(findprotodie(ctxt, "type.runtime.hchan"))
	if sudog == nil || waitq == nil || hchan == nil {
		return
	}

	sudogsize := int(getattr(sudog, dwarf.DW_AT_byte_size).Value)

	for ; die != nil; die = die.Link {
		if die.Abbrev != dwarf.DW_ABRV_CHANTYPE {
			continue
		}
		elemgotype := getattr(die, dwarf.DW_AT_type).Data.(*sym.Symbol)
		elemname := elemgotype.Name[5:]
		elemtype := walksymtypedef(ctxt, defgotype(ctxt, elemgotype))

		// sudog<T>
		dwss := mkinternaltype(ctxt, dwarf.DW_ABRV_STRUCTTYPE, "sudog", elemname, "", func(dws *dwarf.DWDie) {
			copychildren(ctxt, dws, sudog)
			substitutetype(dws, "elem", defptrto(ctxt, elemtype))
			newattr(dws, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, int64(sudogsize), nil)
		})

		// waitq<T>
		dwws := mkinternaltype(ctxt, dwarf.DW_ABRV_STRUCTTYPE, "waitq", elemname, "", func(dww *dwarf.DWDie) {

			copychildren(ctxt, dww, waitq)
			substitutetype(dww, "first", defptrto(ctxt, dwss))
			substitutetype(dww, "last", defptrto(ctxt, dwss))
			newattr(dww, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, getattr(waitq, dwarf.DW_AT_byte_size).Value, nil)
		})

		// hchan<T>
		dwhs := mkinternaltype(ctxt, dwarf.DW_ABRV_STRUCTTYPE, "hchan", elemname, "", func(dwh *dwarf.DWDie) {
			copychildren(ctxt, dwh, hchan)
			substitutetype(dwh, "recvq", dwws)
			substitutetype(dwh, "sendq", dwws)
			newattr(dwh, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, getattr(hchan, dwarf.DW_AT_byte_size).Value, nil)
		})

		newrefattr(die, dwarf.DW_AT_type, defptrto(ctxt, dwhs))
	}
}

func dwarfDefineGlobal(ctxt *Link, s *sym.Symbol, str string, v int64, gotype *sym.Symbol) {
	lib := s.Lib
	if lib == nil {
		lib = ctxt.LibraryByPkg["runtime"]
	}
	dv := newdie(ctxt, ctxt.compUnitByPackage[lib].dwinfo, dwarf.DW_ABRV_VARIABLE, str, int(s.Version))
	newabslocexprattr(dv, v, s)
	if !s.IsFileLocal() {
		newattr(dv, dwarf.DW_AT_external, dwarf.DW_CLS_FLAG, 1, 0)
	}
	dt := defgotype(ctxt, gotype)
	newrefattr(dv, dwarf.DW_AT_type, dt)
}

// For use with pass.c::genasmsym
func defdwsymb(ctxt *Link, s *sym.Symbol, str string, t SymbolType, v int64, gotype *sym.Symbol) {
	if strings.HasPrefix(str, "go.string.") {
		return
	}
	if strings.HasPrefix(str, "runtime.gcbits.") {
		return
	}

	switch t {
	case DataSym, BSSSym:
		switch s.Type {
		case sym.SDATA, sym.SNOPTRDATA, sym.STYPE, sym.SBSS, sym.SNOPTRBSS, sym.STLSBSS:
			// ok
		case sym.SRODATA:
			if gotype != nil {
				defgotype(ctxt, gotype)
			}
			return
		default:
			return
		}
		if ctxt.LinkMode != LinkExternal && isStaticTemp(s.Name) {
			return
		}
		dwarfDefineGlobal(ctxt, s, str, v, gotype)

	case AutoSym, ParamSym, DeletedAutoSym:
		defgotype(ctxt, gotype)
	}
}

// createUnitLength creates the initial length field with value v and update
// offset of unit_length if needed.
func createUnitLength(ctxt *Link, s *sym.Symbol, v uint64) {
	if isDwarf64(ctxt) {
		s.AddUint32(ctxt.Arch, 0xFFFFFFFF)
	}
	addDwarfAddrField(ctxt, s, v)
}

// addDwarfAddrField adds a DWARF field in DWARF 64bits or 32bits.
func addDwarfAddrField(ctxt *Link, s *sym.Symbol, v uint64) {
	if isDwarf64(ctxt) {
		s.AddUint(ctxt.Arch, v)
	} else {
		s.AddUint32(ctxt.Arch, uint32(v))
	}
}

// addDwarfAddrRef adds a DWARF pointer in DWARF 64bits or 32bits.
func addDwarfAddrRef(ctxt *Link, s *sym.Symbol, t *sym.Symbol) {
	if isDwarf64(ctxt) {
		adddwarfref(ctxt, s, t, 8)
	} else {
		adddwarfref(ctxt, s, t, 4)
	}
}

// compilationUnit is per-compilation unit (equivalently, per-package)
// debug-related data.
type compilationUnit struct {
	lib       *sym.Library
	consts    *sym.Symbol   // Package constants DIEs
	pcs       []dwarf.Range // PC ranges, relative to textp[0]
	dwinfo    *dwarf.DWDie  // CU root DIE
	funcDIEs  []*sym.Symbol // Function DIE subtrees
	absFnDIEs []*sym.Symbol // Abstract function DIE subtrees
	rangeSyms []*sym.Symbol // symbols for debug_range
}

// calcCompUnitRanges calculates the PC ranges of the compilation units.
func calcCompUnitRanges(ctxt *Link) {
	var prevUnit *compilationUnit
	for _, s := range ctxt.Textp {
		if s.FuncInfo == nil {
			continue
		}
		unit := ctxt.compUnitByPackage[s.Lib]

		// Update PC ranges.
		//
		// We don't simply compare the end of the previous
		// symbol with the start of the next because there's
		// often a little padding between them. Instead, we
		// only create boundaries between symbols from
		// different units.
		if prevUnit != unit {
			unit.pcs = append(unit.pcs, dwarf.Range{Start: s.Value - unit.lib.Textp[0].Value})
			prevUnit = unit
		}
		unit.pcs[len(unit.pcs)-1].End = s.Value - unit.lib.Textp[0].Value + s.Size
	}
}

func movetomodule(ctxt *Link, parent *dwarf.DWDie) {
	runtimelib := ctxt.LibraryByPkg["runtime"]
	die := ctxt.compUnitByPackage[runtimelib].dwinfo.Child
	if die == nil {
		ctxt.compUnitByPackage[runtimelib].dwinfo.Child = parent.Child
		return
	}
	for die.Link != nil {
		die = die.Link
	}
	die.Link = parent.Child
}

// If the pcln table contains runtime/proc.go, use that to set gdbscript path.
func finddebugruntimepath(s *sym.Symbol) {
	if gdbscript != "" {
		return
	}

	for i := range s.FuncInfo.File {
		f := s.FuncInfo.File[i]
		// We can't use something that may be dead-code
		// eliminated from a binary here. proc.go contains
		// main and the scheduler, so it's not going anywhere.
		if i := strings.Index(f.Name, "runtime/proc.go"); i >= 0 {
			gdbscript = f.Name[:i] + "runtime/runtime-gdb.py"
			break
		}
	}
}

/*
 * Generate a sequence of opcodes that is as short as possible.
 * See section 6.2.5
 */
const (
	LINE_BASE   = -4
	LINE_RANGE  = 10
	PC_RANGE    = (255 - OPCODE_BASE) / LINE_RANGE
	OPCODE_BASE = 11
)

func putpclcdelta(linkctxt *Link, ctxt dwarf.Context, s *sym.Symbol, deltaPC uint64, deltaLC int64) {
	// Choose a special opcode that minimizes the number of bytes needed to
	// encode the remaining PC delta and LC delta.
	var opcode int64
	if deltaLC < LINE_BASE {
		if deltaPC >= PC_RANGE {
			opcode = OPCODE_BASE + (LINE_RANGE * PC_RANGE)
		} else {
			opcode = OPCODE_BASE + (LINE_RANGE * int64(deltaPC))
		}
	} else if deltaLC < LINE_BASE+LINE_RANGE {
		if deltaPC >= PC_RANGE {
			opcode = OPCODE_BASE + (deltaLC - LINE_BASE) + (LINE_RANGE * PC_RANGE)
			if opcode > 255 {
				opcode -= LINE_RANGE
			}
		} else {
			opcode = OPCODE_BASE + (deltaLC - LINE_BASE) + (LINE_RANGE * int64(deltaPC))
		}
	} else {
		if deltaPC <= PC_RANGE {
			opcode = OPCODE_BASE + (LINE_RANGE - 1) + (LINE_RANGE * int64(deltaPC))
			if opcode > 255 {
				opcode = 255
			}
		} else {
			// Use opcode 249 (pc+=23, lc+=5) or 255 (pc+=24, lc+=1).
			//
			// Let x=deltaPC-PC_RANGE.  If we use opcode 255, x will be the remaining
			// deltaPC that we need to encode separately before emitting 255.  If we
			// use opcode 249, we will need to encode x+1.  If x+1 takes one more
			// byte to encode than x, then we use opcode 255.
			//
			// In all other cases x and x+1 take the same number of bytes to encode,
			// so we use opcode 249, which may save us a byte in encoding deltaLC,
			// for similar reasons.
			switch deltaPC - PC_RANGE {
			// PC_RANGE is the largest deltaPC we can encode in one byte, using
			// DW_LNS_const_add_pc.
			//
			// (1<<16)-1 is the largest deltaPC we can encode in three bytes, using
			// DW_LNS_fixed_advance_pc.
			//
			// (1<<(7n))-1 is the largest deltaPC we can encode in n+1 bytes for
			// n=1,3,4,5,..., using DW_LNS_advance_pc.
			case PC_RANGE, (1 << 7) - 1, (1 << 16) - 1, (1 << 21) - 1, (1 << 28) - 1,
				(1 << 35) - 1, (1 << 42) - 1, (1 << 49) - 1, (1 << 56) - 1, (1 << 63) - 1:
				opcode = 255
			default:
				opcode = OPCODE_BASE + LINE_RANGE*PC_RANGE - 1 // 249
			}
		}
	}
	if opcode < OPCODE_BASE || opcode > 255 {
		panic(fmt.Sprintf("produced invalid special opcode %d", opcode))
	}

	// Subtract from deltaPC and deltaLC the amounts that the opcode will add.
	deltaPC -= uint64((opcode - OPCODE_BASE) / LINE_RANGE)
	deltaLC -= (opcode-OPCODE_BASE)%LINE_RANGE + LINE_BASE

	// Encode deltaPC.
	if deltaPC != 0 {
		if deltaPC <= PC_RANGE {
			// Adjust the opcode so that we can use the 1-byte DW_LNS_const_add_pc
			// instruction.
			opcode -= LINE_RANGE * int64(PC_RANGE-deltaPC)
			if opcode < OPCODE_BASE {
				panic(fmt.Sprintf("produced invalid special opcode %d", opcode))
			}
			s.AddUint8(dwarf.DW_LNS_const_add_pc)
		} else if (1<<14) <= deltaPC && deltaPC < (1<<16) {
			s.AddUint8(dwarf.DW_LNS_fixed_advance_pc)
			s.AddUint16(linkctxt.Arch, uint16(deltaPC))
		} else {
			s.AddUint8(dwarf.DW_LNS_advance_pc)
			dwarf.Uleb128put(ctxt, s, int64(deltaPC))
		}
	}

	// Encode deltaLC.
	if deltaLC != 0 {
		s.AddUint8(dwarf.DW_LNS_advance_line)
		dwarf.Sleb128put(ctxt, s, deltaLC)
	}

	// Output the special opcode.
	s.AddUint8(uint8(opcode))
}

/*
 * Walk prog table, emit line program and build DIE tree.
 */

func getCompilationDir() string {
	// OSX requires this be set to something, but it's not easy to choose
	// a value. Linking takes place in a temporary directory, so there's
	// no point including it here. Paths in the file table are usually
	// absolute, in which case debuggers will ignore this value. -trimpath
	// produces relative paths, but we don't know where they start, so
	// all we can do here is try not to make things worse.
	return "."
}

func importInfoSymbol(ctxt *Link, dsym *sym.Symbol) {
	dsym.Attr |= sym.AttrNotInSymbolTable | sym.AttrReachable
	dsym.Type = sym.SDWARFINFO
	for i := range dsym.R {
		r := &dsym.R[i] // Copying sym.Reloc has measurable impact on performance
		if r.Type == objabi.R_DWARFSECREF && r.Sym.Size == 0 {
			n := nameFromDIESym(r.Sym)
			defgotype(ctxt, ctxt.Syms.Lookup("type."+n, 0))
		}
	}
}

func writelines(ctxt *Link, unit *compilationUnit, ls *sym.Symbol) {

	var dwarfctxt dwarf.Context = dwctxt{ctxt}
	is_stmt := uint8(1) // initially = recommended default_is_stmt = 1, tracks is_stmt toggles.

	unitstart := int64(-1)
	headerstart := int64(-1)
	headerend := int64(-1)

	newattr(unit.dwinfo, dwarf.DW_AT_stmt_list, dwarf.DW_CLS_PTR, ls.Size, ls)

	// Write .debug_line Line Number Program Header (sec 6.2.4)
	// Fields marked with (*) must be changed for 64-bit dwarf
	unitLengthOffset := ls.Size
	createUnitLength(ctxt, ls, 0) // unit_length (*), filled in at end
	unitstart = ls.Size
	ls.AddUint16(ctxt.Arch, 2) // dwarf version (appendix F) -- version 3 is incompatible w/ XCode 9.0's dsymutil, latest supported on OSX 10.12 as of 2018-05
	headerLengthOffset := ls.Size
	addDwarfAddrField(ctxt, ls, 0) // header_length (*), filled in at end
	headerstart = ls.Size

	// cpos == unitstart + 4 + 2 + 4
	ls.AddUint8(1)                // minimum_instruction_length
	ls.AddUint8(is_stmt)          // default_is_stmt
	ls.AddUint8(LINE_BASE & 0xFF) // line_base
	ls.AddUint8(LINE_RANGE)       // line_range
	ls.AddUint8(OPCODE_BASE)      // opcode_base
	ls.AddUint8(0)                // standard_opcode_lengths[1]
	ls.AddUint8(1)                // standard_opcode_lengths[2]
	ls.AddUint8(1)                // standard_opcode_lengths[3]
	ls.AddUint8(1)                // standard_opcode_lengths[4]
	ls.AddUint8(1)                // standard_opcode_lengths[5]
	ls.AddUint8(0)                // standard_opcode_lengths[6]
	ls.AddUint8(0)                // standard_opcode_lengths[7]
	ls.AddUint8(0)                // standard_opcode_lengths[8]
	ls.AddUint8(1)                // standard_opcode_lengths[9]
	ls.AddUint8(0)                // standard_opcode_lengths[10]
	ls.AddUint8(0)                // include_directories  (empty)

	// Create the file table. fileNums maps from global file
	// indexes (created by numberfile) to CU-local indexes.
	fileNums := make(map[int]int)
	for _, s := range unit.lib.Textp { // textp has been dead-code-eliminated already.
		dsym := dwarfFuncSym(ctxt, s, dwarf.InfoPrefix, true)
		for _, f := range s.FuncInfo.File {
			if _, ok := fileNums[int(f.Value)]; ok {
				continue
			}
			// File indexes are 1-based.
			fileNums[int(f.Value)] = len(fileNums) + 1
			Addstring(ls, applyBuildPathPrefixMap(f.Name))
			ls.AddUint8(0)
			ls.AddUint8(0)
			ls.AddUint8(0)
		}
		for ri := 0; ri < len(dsym.R); ri++ {
			r := &dsym.R[ri]
			if r.Type != objabi.R_DWARFFILEREF {
				continue
			}
			// A file that is only mentioned in an inlined subroutine will appear
			// as a R_DWARFFILEREF but not in s.FuncInfo.File
			if _, ok := fileNums[int(r.Sym.Value)]; ok {
				continue
			}
			fileNums[int(r.Sym.Value)] = len(fileNums) + 1
			Addstring(ls, r.Sym.Name)
			ls.AddUint8(0)
			ls.AddUint8(0)
			ls.AddUint8(0)
		}
	}

	// 4 zeros: the string termination + 3 fields.
	ls.AddUint8(0)
	// terminate file_names.
	headerend = ls.Size

	ls.AddUint8(0) // start extended opcode
	dwarf.Uleb128put(dwarfctxt, ls, 1+int64(ctxt.Arch.PtrSize))
	ls.AddUint8(dwarf.DW_LNE_set_address)

	s := unit.lib.Textp[0]
	pc := s.Value
	line := 1
	file := 1
	ls.AddAddr(ctxt.Arch, s)

	var pcfile Pciter
	var pcline Pciter
	var pcstmt Pciter
	for i, s := range unit.lib.Textp {
		finddebugruntimepath(s)

		pciterinit(ctxt, &pcfile, &s.FuncInfo.Pcfile)
		pciterinit(ctxt, &pcline, &s.FuncInfo.Pcline)

		isStmtSym := dwarfFuncSym(ctxt, s, dwarf.IsStmtPrefix, false)
		if isStmtSym != nil && len(isStmtSym.P) > 0 {
			pciterinit(ctxt, &pcstmt, &sym.Pcdata{P: isStmtSym.P})
		} else {
			// Assembly files lack a pcstmt section, we assume that every instruction
			// is a valid statement.
			pcstmt.done = 1
			pcstmt.value = 1
		}

		var thispc uint32
		// TODO this loop looks like it could exit with work remaining.
		for pcfile.done == 0 && pcline.done == 0 {
			// Only changed if it advanced
			if int32(file) != pcfile.value {
				ls.AddUint8(dwarf.DW_LNS_set_file)
				idx, ok := fileNums[int(pcfile.value)]
				if !ok {
					Exitf("pcln table file missing from DWARF line table")
				}
				dwarf.Uleb128put(dwarfctxt, ls, int64(idx))
				file = int(pcfile.value)
			}

			// Only changed if it advanced
			if is_stmt != uint8(pcstmt.value) {
				new_stmt := uint8(pcstmt.value)
				switch new_stmt &^ 1 {
				case obj.PrologueEnd:
					ls.AddUint8(uint8(dwarf.DW_LNS_set_prologue_end))
				case obj.EpilogueBegin:
					// TODO if there is a use for this, add it.
					// Don't forget to increase OPCODE_BASE by 1 and add entry for standard_opcode_lengths[11]
				}
				new_stmt &= 1
				if is_stmt != new_stmt {
					is_stmt = new_stmt
					ls.AddUint8(uint8(dwarf.DW_LNS_negate_stmt))
				}
			}

			// putpcldelta makes a row in the DWARF matrix, always, even if line is unchanged.
			putpclcdelta(ctxt, dwarfctxt, ls, uint64(s.Value+int64(thispc)-pc), int64(pcline.value)-int64(line))

			pc = s.Value + int64(thispc)
			line = int(pcline.value)

			// Take the minimum step forward for the three iterators
			thispc = pcfile.nextpc
			if pcline.nextpc < thispc {
				thispc = pcline.nextpc
			}
			if pcstmt.done == 0 && pcstmt.nextpc < thispc {
				thispc = pcstmt.nextpc
			}

			if pcfile.nextpc == thispc {
				pciternext(&pcfile)
			}
			if pcstmt.done == 0 && pcstmt.nextpc == thispc {
				pciternext(&pcstmt)
			}
			if pcline.nextpc == thispc {
				pciternext(&pcline)
			}
		}
		if is_stmt == 0 && i < len(unit.lib.Textp)-1 {
			// If there is more than one function, ensure default value is established.
			is_stmt = 1
			ls.AddUint8(uint8(dwarf.DW_LNS_negate_stmt))
		}
	}

	ls.AddUint8(0) // start extended opcode
	dwarf.Uleb128put(dwarfctxt, ls, 1)
	ls.AddUint8(dwarf.DW_LNE_end_sequence)

	if ctxt.HeadType == objabi.Haix {
		saveDwsectCUSize(".debug_line", unit.lib.String(), uint64(ls.Size-unitLengthOffset))
	}
	if isDwarf64(ctxt) {
		ls.SetUint(ctxt.Arch, unitLengthOffset+4, uint64(ls.Size-unitstart)) // +4 because of 0xFFFFFFFF
		ls.SetUint(ctxt.Arch, headerLengthOffset, uint64(headerend-headerstart))
	} else {
		ls.SetUint32(ctxt.Arch, unitLengthOffset, uint32(ls.Size-unitstart))
		ls.SetUint32(ctxt.Arch, headerLengthOffset, uint32(headerend-headerstart))
	}

	// Apply any R_DWARFFILEREF relocations, since we now know the
	// line table file indices for this compilation unit. Note that
	// this loop visits only subprogram DIEs: if the compiler is
	// changed to generate DW_AT_decl_file attributes for other
	// DIE flavors (ex: variables) then those DIEs would need to
	// be included below.
	missing := make(map[int]interface{})
	for _, f := range unit.funcDIEs {
		for ri := range f.R {
			r := &f.R[ri]
			if r.Type != objabi.R_DWARFFILEREF {
				continue
			}
			// Mark relocation as applied (signal to relocsym)
			r.Done = true
			idx, ok := fileNums[int(r.Sym.Value)]
			if ok {
				if int(int32(idx)) != idx {
					Errorf(f, "bad R_DWARFFILEREF relocation: file index overflow")
				}
				if r.Siz != 4 {
					Errorf(f, "bad R_DWARFFILEREF relocation: has size %d, expected 4", r.Siz)
				}
				if r.Off < 0 || r.Off+4 > int32(len(f.P)) {
					Errorf(f, "bad R_DWARFFILEREF relocation offset %d + 4 would write past length %d", r.Off, len(s.P))
					continue
				}
				ctxt.Arch.ByteOrder.PutUint32(f.P[r.Off:r.Off+4], uint32(idx))
			} else {
				_, found := missing[int(r.Sym.Value)]
				if !found {
					Errorf(f, "R_DWARFFILEREF relocation file missing: %v idx %d", r.Sym, r.Sym.Value)
					missing[int(r.Sym.Value)] = nil
				}
			}
		}
	}
}

// writepcranges generates the DW_AT_ranges table for compilation unit cu.
func writepcranges(ctxt *Link, cu *dwarf.DWDie, base *sym.Symbol, pcs []dwarf.Range, ranges *sym.Symbol) {
	var dwarfctxt dwarf.Context = dwctxt{ctxt}

	// Create PC ranges for this CU.
	newattr(cu, dwarf.DW_AT_ranges, dwarf.DW_CLS_PTR, ranges.Size, ranges)
	newattr(cu, dwarf.DW_AT_low_pc, dwarf.DW_CLS_ADDRESS, base.Value, base)
	dwarf.PutRanges(dwarfctxt, ranges, nil, pcs)
}

/*
 *  Emit .debug_frame
 */
const (
	dataAlignmentFactor = -4
)

// appendPCDeltaCFA appends per-PC CFA deltas to b and returns the final slice.
func appendPCDeltaCFA(arch *sys.Arch, b []byte, deltapc, cfa int64) []byte {
	b = append(b, dwarf.DW_CFA_def_cfa_offset_sf)
	b = dwarf.AppendSleb128(b, cfa/dataAlignmentFactor)

	switch {
	case deltapc < 0x40:
		b = append(b, uint8(dwarf.DW_CFA_advance_loc+deltapc))
	case deltapc < 0x100:
		b = append(b, dwarf.DW_CFA_advance_loc1)
		b = append(b, uint8(deltapc))
	case deltapc < 0x10000:
		b = append(b, dwarf.DW_CFA_advance_loc2, 0, 0)
		arch.ByteOrder.PutUint16(b[len(b)-2:], uint16(deltapc))
	default:
		b = append(b, dwarf.DW_CFA_advance_loc4, 0, 0, 0, 0)
		arch.ByteOrder.PutUint32(b[len(b)-4:], uint32(deltapc))
	}
	return b
}

func writeframes(ctxt *Link, syms []*sym.Symbol) []*sym.Symbol {
	var dwarfctxt dwarf.Context = dwctxt{ctxt}
	fs := ctxt.Syms.Lookup(".debug_frame", 0)
	fs.Type = sym.SDWARFSECT
	syms = append(syms, fs)

	// Emit the CIE, Section 6.4.1
	cieReserve := uint32(16)
	if haslinkregister(ctxt) {
		cieReserve = 32
	}
	createUnitLength(ctxt, fs, uint64(cieReserve))             // initial length, must be multiple of thearch.ptrsize
	addDwarfAddrField(ctxt, fs, 0xffffffff)                    // cid.
	fs.AddUint8(3)                                             // dwarf version (appendix F)
	fs.AddUint8(0)                                             // augmentation ""
	dwarf.Uleb128put(dwarfctxt, fs, 1)                         // code_alignment_factor
	dwarf.Sleb128put(dwarfctxt, fs, dataAlignmentFactor)       // all CFI offset calculations include multiplication with this factor
	dwarf.Uleb128put(dwarfctxt, fs, int64(thearch.Dwarfreglr)) // return_address_register

	fs.AddUint8(dwarf.DW_CFA_def_cfa)                          // Set the current frame address..
	dwarf.Uleb128put(dwarfctxt, fs, int64(thearch.Dwarfregsp)) // ...to use the value in the platform's SP register (defined in l.go)...
	if haslinkregister(ctxt) {
		dwarf.Uleb128put(dwarfctxt, fs, int64(0)) // ...plus a 0 offset.

		fs.AddUint8(dwarf.DW_CFA_same_value) // The platform's link register is unchanged during the prologue.
		dwarf.Uleb128put(dwarfctxt, fs, int64(thearch.Dwarfreglr))

		fs.AddUint8(dwarf.DW_CFA_val_offset)                       // The previous value...
		dwarf.Uleb128put(dwarfctxt, fs, int64(thearch.Dwarfregsp)) // ...of the platform's SP register...
		dwarf.Uleb128put(dwarfctxt, fs, int64(0))                  // ...is CFA+0.
	} else {
		dwarf.Uleb128put(dwarfctxt, fs, int64(ctxt.Arch.PtrSize)) // ...plus the word size (because the call instruction implicitly adds one word to the frame).

		fs.AddUint8(dwarf.DW_CFA_offset_extended)                                      // The previous value...
		dwarf.Uleb128put(dwarfctxt, fs, int64(thearch.Dwarfreglr))                     // ...of the return address...
		dwarf.Uleb128put(dwarfctxt, fs, int64(-ctxt.Arch.PtrSize)/dataAlignmentFactor) // ...is saved at [CFA - (PtrSize/4)].
	}

	// 4 is to exclude the length field.
	pad := int64(cieReserve) + 4 - fs.Size

	if pad < 0 {
		Exitf("dwarf: cieReserve too small by %d bytes.", -pad)
	}

	fs.AddBytes(zeros[:pad])

	var deltaBuf []byte
	var pcsp Pciter
	for _, s := range ctxt.Textp {
		if s.FuncInfo == nil {
			continue
		}

		// Emit a FDE, Section 6.4.1.
		// First build the section contents into a byte buffer.
		deltaBuf = deltaBuf[:0]
		for pciterinit(ctxt, &pcsp, &s.FuncInfo.Pcsp); pcsp.done == 0; pciternext(&pcsp) {
			nextpc := pcsp.nextpc

			// pciterinit goes up to the end of the function,
			// but DWARF expects us to stop just before the end.
			if int64(nextpc) == s.Size {
				nextpc--
				if nextpc < pcsp.pc {
					continue
				}
			}

			if haslinkregister(ctxt) {
				// TODO(bryanpkc): This is imprecise. In general, the instruction
				// that stores the return address to the stack frame is not the
				// same one that allocates the frame.
				if pcsp.value > 0 {
					// The return address is preserved at (CFA-frame_size)
					// after a stack frame has been allocated.
					deltaBuf = append(deltaBuf, dwarf.DW_CFA_offset_extended_sf)
					deltaBuf = dwarf.AppendUleb128(deltaBuf, uint64(thearch.Dwarfreglr))
					deltaBuf = dwarf.AppendSleb128(deltaBuf, -int64(pcsp.value)/dataAlignmentFactor)
				} else {
					// The return address is restored into the link register
					// when a stack frame has been de-allocated.
					deltaBuf = append(deltaBuf, dwarf.DW_CFA_same_value)
					deltaBuf = dwarf.AppendUleb128(deltaBuf, uint64(thearch.Dwarfreglr))
				}
				deltaBuf = appendPCDeltaCFA(ctxt.Arch, deltaBuf, int64(nextpc)-int64(pcsp.pc), int64(pcsp.value))
			} else {
				deltaBuf = appendPCDeltaCFA(ctxt.Arch, deltaBuf, int64(nextpc)-int64(pcsp.pc), int64(ctxt.Arch.PtrSize)+int64(pcsp.value))
			}
		}
		pad := int(Rnd(int64(len(deltaBuf)), int64(ctxt.Arch.PtrSize))) - len(deltaBuf)
		deltaBuf = append(deltaBuf, zeros[:pad]...)

		// Emit the FDE header, Section 6.4.1.
		//	4 bytes: length, must be multiple of thearch.ptrsize
		//	4 bytes: Pointer to the CIE above, at offset 0
		//	ptrsize: initial location
		//	ptrsize: address range
		fs.AddUint32(ctxt.Arch, uint32(4+2*ctxt.Arch.PtrSize+len(deltaBuf))) // length (excludes itself)
		if ctxt.LinkMode == LinkExternal {
			addDwarfAddrRef(ctxt, fs, fs)
		} else {
			addDwarfAddrField(ctxt, fs, 0) // CIE offset
		}
		fs.AddAddr(ctxt.Arch, s)
		fs.AddUintXX(ctxt.Arch, uint64(s.Size), ctxt.Arch.PtrSize) // address range
		fs.AddBytes(deltaBuf)
	}
	return syms
}

/*
 *  Walk DWarfDebugInfoEntries, and emit .debug_info
 */
const (
	COMPUNITHEADERSIZE = 4 + 2 + 4 + 1
)

func writeinfo(ctxt *Link, syms []*sym.Symbol, units []*compilationUnit, abbrevsym *sym.Symbol) []*sym.Symbol {
	infosec := ctxt.Syms.Lookup(".debug_info", 0)
	infosec.Type = sym.SDWARFINFO
	infosec.Attr |= sym.AttrReachable
	syms = append(syms, infosec)

	var dwarfctxt dwarf.Context = dwctxt{ctxt}

	for _, u := range units {
		compunit := u.dwinfo
		s := dtolsym(compunit.Sym)

		if len(u.lib.Textp) == 0 && u.dwinfo.Child == nil {
			continue
		}

		// Write .debug_info Compilation Unit Header (sec 7.5.1)
		// Fields marked with (*) must be changed for 64-bit dwarf
		// This must match COMPUNITHEADERSIZE above.
		createUnitLength(ctxt, s, 0) // unit_length (*), will be filled in later.
		s.AddUint16(ctxt.Arch, 4)    // dwarf version (appendix F)

		// debug_abbrev_offset (*)
		addDwarfAddrRef(ctxt, s, abbrevsym)

		s.AddUint8(uint8(ctxt.Arch.PtrSize)) // address_size

		dwarf.Uleb128put(dwarfctxt, s, int64(compunit.Abbrev))
		dwarf.PutAttrs(dwarfctxt, s, compunit.Abbrev, compunit.Attr)

		cu := []*sym.Symbol{s}
		cu = append(cu, u.absFnDIEs...)
		cu = append(cu, u.funcDIEs...)
		if u.consts != nil {
			cu = append(cu, u.consts)
		}
		cu = putdies(ctxt, dwarfctxt, cu, compunit.Child)
		var cusize int64
		for _, child := range cu {
			cusize += child.Size
		}
		// Save size for AIX symbol table.
		if ctxt.HeadType == objabi.Haix {
			saveDwsectCUSize(".debug_info", getPkgFromCUSym(s), uint64(cusize))
		}
		if isDwarf64(ctxt) {
			cusize -= 12                            // exclude the length field.
			s.SetUint(ctxt.Arch, 4, uint64(cusize)) // 4 because of 0XFFFFFFFF
		} else {
			cusize -= 4 // exclude the length field.
			s.SetUint32(ctxt.Arch, 0, uint32(cusize))
		}
		// Leave a breadcrumb for writepub. This does not
		// appear in the DWARF output.
		newattr(compunit, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, cusize, 0)
		syms = append(syms, cu...)
	}
	return syms
}

/*
 *  Emit .debug_pubnames/_types.  _info must have been written before,
 *  because we need die->offs and infoo/infosize;
 */
func ispubname(die *dwarf.DWDie) bool {
	switch die.Abbrev {
	case dwarf.DW_ABRV_FUNCTION, dwarf.DW_ABRV_VARIABLE:
		a := getattr(die, dwarf.DW_AT_external)
		return a != nil && a.Value != 0
	}

	return false
}

func ispubtype(die *dwarf.DWDie) bool {
	return die.Abbrev >= dwarf.DW_ABRV_NULLTYPE
}

func writepub(ctxt *Link, sname string, ispub func(*dwarf.DWDie) bool, syms []*sym.Symbol) []*sym.Symbol {
	s := ctxt.Syms.Lookup(sname, 0)
	s.Type = sym.SDWARFSECT
	syms = append(syms, s)

	for _, u := range ctxt.compUnits {
		if len(u.lib.Textp) == 0 && u.dwinfo.Child == nil {
			continue
		}
		compunit := u.dwinfo
		sectionstart := s.Size
		culength := uint32(getattr(compunit, dwarf.DW_AT_byte_size).Value) + 4

		// Write .debug_pubnames/types	Header (sec 6.1.1)
		createUnitLength(ctxt, s, 0)                    // unit_length (*), will be filled in later.
		s.AddUint16(ctxt.Arch, 2)                       // dwarf version (appendix F)
		addDwarfAddrRef(ctxt, s, dtolsym(compunit.Sym)) // debug_info_offset (of the Comp unit Header)
		addDwarfAddrField(ctxt, s, uint64(culength))    // debug_info_length

		for die := compunit.Child; die != nil; die = die.Link {
			if !ispub(die) {
				continue
			}
			dwa := getattr(die, dwarf.DW_AT_name)
			name := dwa.Data.(string)
			if die.Sym == nil {
				fmt.Println("Missing sym for ", name)
			}
			addDwarfAddrRef(ctxt, s, dtolsym(die.Sym))
			Addstring(s, name)
		}

		addDwarfAddrField(ctxt, s, 0) // Null offset

		// On AIX, save the current size of this compilation unit.
		if ctxt.HeadType == objabi.Haix {
			saveDwsectCUSize(sname, getPkgFromCUSym(dtolsym(compunit.Sym)), uint64(s.Size-sectionstart))
		}
		if isDwarf64(ctxt) {
			s.SetUint(ctxt.Arch, sectionstart+4, uint64(s.Size-sectionstart)-12) // exclude the length field.
		} else {
			s.SetUint32(ctxt.Arch, sectionstart, uint32(s.Size-sectionstart)-4) // exclude the length field.
		}
	}

	return syms
}

func writegdbscript(ctxt *Link, syms []*sym.Symbol) []*sym.Symbol {
	// TODO (aix): make it available
	if ctxt.HeadType == objabi.Haix {
		return syms
	}
	if ctxt.LinkMode == LinkExternal && ctxt.HeadType == objabi.Hwindows && ctxt.BuildMode == BuildModeCArchive {
		// gcc on Windows places .debug_gdb_scripts in the wrong location, which
		// causes the program not to run. See https://golang.org/issue/20183
		// Non c-archives can avoid this issue via a linker script
		// (see fix near writeGDBLinkerScript).
		// c-archive users would need to specify the linker script manually.
		// For UX it's better not to deal with this.
		return syms
	}

	if gdbscript != "" {
		s := ctxt.Syms.Lookup(".debug_gdb_scripts", 0)
		s.Type = sym.SDWARFSECT
		syms = append(syms, s)
		s.AddUint8(1) // magic 1 byte?
		Addstring(s, gdbscript)
	}

	return syms
}

var prototypedies map[string]*dwarf.DWDie

func dwarfEnabled(ctxt *Link) bool {
	if *FlagW { // disable dwarf
		return false
	}
	if *FlagS && ctxt.HeadType != objabi.Hdarwin {
		return false
	}
	if ctxt.HeadType == objabi.Hplan9 || ctxt.HeadType == objabi.Hjs {
		return false
	}

	if ctxt.LinkMode == LinkExternal {
		switch {
		case ctxt.IsELF:
		case ctxt.HeadType == objabi.Hdarwin:
		case ctxt.HeadType == objabi.Hwindows:
		default:
			return false
		}
	}

	return true
}

// dwarfGenerateDebugInfo generated debug info entries for all types,
// variables and functions in the program.
// Along with dwarfGenerateDebugSyms they are the two main entry points into
// dwarf generation: dwarfGenerateDebugInfo does all the work that should be
// done before symbol names are mangled while dwarfgeneratedebugsyms does
// all the work that can only be done after addresses have been assigned to
// text symbols.
func dwarfGenerateDebugInfo(ctxt *Link) {
	if !dwarfEnabled(ctxt) {
		return
	}

	ctxt.compUnitByPackage = make(map[*sym.Library]*compilationUnit)

	// Forctxt.Diagnostic messages.
	newattr(&dwtypes, dwarf.DW_AT_name, dwarf.DW_CLS_STRING, int64(len("dwtypes")), "dwtypes")

	// Some types that must exist to define other ones.
	newdie(ctxt, &dwtypes, dwarf.DW_ABRV_NULLTYPE, "<unspecified>", 0)

	newdie(ctxt, &dwtypes, dwarf.DW_ABRV_NULLTYPE, "void", 0)
	newdie(ctxt, &dwtypes, dwarf.DW_ABRV_BARE_PTRTYPE, "unsafe.Pointer", 0)

	die := newdie(ctxt, &dwtypes, dwarf.DW_ABRV_BASETYPE, "uintptr", 0) // needed for array size
	newattr(die, dwarf.DW_AT_encoding, dwarf.DW_CLS_CONSTANT, dwarf.DW_ATE_unsigned, 0)
	newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, int64(ctxt.Arch.PtrSize), 0)
	newattr(die, dwarf.DW_AT_go_kind, dwarf.DW_CLS_CONSTANT, objabi.KindUintptr, 0)
	newattr(die, dwarf.DW_AT_go_runtime_type, dwarf.DW_CLS_ADDRESS, 0, lookupOrDiag(ctxt, "type.uintptr"))

	// Prototypes needed for type synthesis.
	prototypedies = map[string]*dwarf.DWDie{
		"type.runtime.stringStructDWARF": nil,
		"type.runtime.slice":             nil,
		"type.runtime.hmap":              nil,
		"type.runtime.bmap":              nil,
		"type.runtime.sudog":             nil,
		"type.runtime.waitq":             nil,
		"type.runtime.hchan":             nil,
	}

	// Needed by the prettyprinter code for interface inspection.
	for _, typ := range []string{
		"type.runtime._type",
		"type.runtime.arraytype",
		"type.runtime.chantype",
		"type.runtime.functype",
		"type.runtime.maptype",
		"type.runtime.ptrtype",
		"type.runtime.slicetype",
		"type.runtime.structtype",
		"type.runtime.interfacetype",
		"type.runtime.itab",
		"type.runtime.imethod"} {
		defgotype(ctxt, lookupOrDiag(ctxt, typ))
	}

	// fake root DIE for compile unit DIEs
	var dwroot dwarf.DWDie

	for _, lib := range ctxt.Library {
		unit := &compilationUnit{lib: lib}
		if s := ctxt.Syms.ROLookup(dwarf.ConstInfoPrefix+lib.Pkg, 0); s != nil {
			importInfoSymbol(ctxt, s)
			unit.consts = s
		}
		ctxt.compUnits = append(ctxt.compUnits, unit)
		ctxt.compUnitByPackage[lib] = unit

		unit.dwinfo = newdie(ctxt, &dwroot, dwarf.DW_ABRV_COMPUNIT, unit.lib.Pkg, 0)
		newattr(unit.dwinfo, dwarf.DW_AT_language, dwarf.DW_CLS_CONSTANT, int64(dwarf.DW_LANG_Go), 0)
		// OS X linker requires compilation dir or absolute path in comp unit name to output debug info.
		compDir := applyBuildPathPrefixMap(getCompilationDir())
		// TODO: Make this be the actual compilation directory, not
		// the linker directory. If we move CU construction into the
		// compiler, this should happen naturally.
		newattr(unit.dwinfo, dwarf.DW_AT_comp_dir, dwarf.DW_CLS_STRING, int64(len(compDir)), compDir)
		producerExtra := ctxt.Syms.Lookup(dwarf.CUInfoPrefix+"producer."+unit.lib.Pkg, 0)
		producer := "Go cmd/compile " + objabi.Version
		if len(producerExtra.P) > 0 {
			// We put a semicolon before the flags to clearly
			// separate them from the version, which can be long
			// and have lots of weird things in it in development
			// versions. We promise not to put a semicolon in the
			// version, so it should be safe for readers to scan
			// forward to the semicolon.
			producer += "; " + string(producerExtra.P)
		}
		newattr(unit.dwinfo, dwarf.DW_AT_producer, dwarf.DW_CLS_STRING, int64(len(producer)), producer)

		if len(lib.Textp) == 0 {
			unit.dwinfo.Abbrev = dwarf.DW_ABRV_COMPUNIT_TEXTLESS
		}

		// Scan all functions in this compilation unit, create DIEs for all
		// referenced types, create the file table for debug_line, find all
		// referenced abstract functions.
		// Collect all debug_range symbols in unit.rangeSyms
		for _, s := range lib.Textp { // textp has been dead-code-eliminated already.
			dsym := dwarfFuncSym(ctxt, s, dwarf.InfoPrefix, false)
			dsym.Attr |= sym.AttrNotInSymbolTable | sym.AttrReachable
			dsym.Type = sym.SDWARFINFO
			unit.funcDIEs = append(unit.funcDIEs, dsym)

			rangeSym := dwarfFuncSym(ctxt, s, dwarf.RangePrefix, false)
			if rangeSym != nil && rangeSym.Size > 0 {
				rangeSym.Attr |= sym.AttrReachable | sym.AttrNotInSymbolTable
				rangeSym.Type = sym.SDWARFRANGE
				// LLVM doesn't support base address entries. Strip them out so LLDB and dsymutil don't get confused.
				if ctxt.HeadType == objabi.Hdarwin {
					removeDwarfAddrListBaseAddress(ctxt, dsym, rangeSym, false)
				}
				unit.rangeSyms = append(unit.rangeSyms, rangeSym)
			}

			for ri := 0; ri < len(dsym.R); ri++ {
				r := &dsym.R[ri]
				if r.Type == objabi.R_DWARFSECREF {
					rsym := r.Sym
					if strings.HasPrefix(rsym.Name, dwarf.InfoPrefix) && strings.HasSuffix(rsym.Name, dwarf.AbstractFuncSuffix) && !rsym.Attr.OnList() {
						// abstract function
						rsym.Attr |= sym.AttrOnList
						unit.absFnDIEs = append(unit.absFnDIEs, rsym)
						importInfoSymbol(ctxt, rsym)
					} else if rsym.Size == 0 {
						// a type we do not have a DIE for
						n := nameFromDIESym(rsym)
						defgotype(ctxt, ctxt.Syms.Lookup("type."+n, 0))
					}
				}
			}
		}
	}

	// Create DIEs for global variables and the types they use.
	genasmsym(ctxt, defdwsymb)

	synthesizestringtypes(ctxt, dwtypes.Child)
	synthesizeslicetypes(ctxt, dwtypes.Child)
	synthesizemaptypes(ctxt, dwtypes.Child)
	synthesizechantypes(ctxt, dwtypes.Child)
}

// dwarfGenerateDebugSyms constructs debug_line, debug_frame, debug_loc,
// debug_pubnames and debug_pubtypes. It also writes out the debug_info
// section using symbols generated in dwarfGenerateDebugInfo.
func dwarfGenerateDebugSyms(ctxt *Link) {
	if !dwarfEnabled(ctxt) {
		return
	}

	if ctxt.Debugvlog != 0 {
		ctxt.Logf("%5.2f dwarf\n", Cputime())
	}

	abbrev := writeabbrev(ctxt)
	syms := []*sym.Symbol{abbrev}

	calcCompUnitRanges(ctxt)
	sort.Sort(compilationUnitByStartPC(ctxt.compUnits))

	// Write per-package line and range tables and start their CU DIEs.
	debugLine := ctxt.Syms.Lookup(".debug_line", 0)
	debugLine.Type = sym.SDWARFSECT
	debugRanges := ctxt.Syms.Lookup(".debug_ranges", 0)
	debugRanges.Type = sym.SDWARFRANGE
	debugRanges.Attr |= sym.AttrReachable
	syms = append(syms, debugLine)
	for _, u := range ctxt.compUnits {
		reversetree(&u.dwinfo.Child)
		if u.dwinfo.Abbrev == dwarf.DW_ABRV_COMPUNIT_TEXTLESS {
			continue
		}
		writelines(ctxt, u, debugLine)
		writepcranges(ctxt, u.dwinfo, u.lib.Textp[0], u.pcs, debugRanges)
	}

	// newdie adds DIEs to the *beginning* of the parent's DIE list.
	// Now that we're done creating DIEs, reverse the trees so DIEs
	// appear in the order they were created.
	reversetree(&dwtypes.Child)
	movetomodule(ctxt, &dwtypes)

	// Need to reorder symbols so sym.SDWARFINFO is after all sym.SDWARFSECT
	// (but we need to generate dies before writepub)
	infosyms := writeinfo(ctxt, nil, ctxt.compUnits, abbrev)

	syms = writeframes(ctxt, syms)
	syms = writepub(ctxt, ".debug_pubnames", ispubname, syms)
	syms = writepub(ctxt, ".debug_pubtypes", ispubtype, syms)
	syms = writegdbscript(ctxt, syms)
	// Now we're done writing SDWARFSECT symbols, so we can write
	// other SDWARF* symbols.
	syms = append(syms, infosyms...)
	syms = collectlocs(ctxt, syms, ctxt.compUnits)
	syms = append(syms, debugRanges)
	for _, unit := range ctxt.compUnits {
		syms = append(syms, unit.rangeSyms...)
	}
	dwarfp = syms
}

func collectlocs(ctxt *Link, syms []*sym.Symbol, units []*compilationUnit) []*sym.Symbol {
	empty := true
	for _, u := range units {
		for _, fn := range u.funcDIEs {
			for i := range fn.R {
				reloc := &fn.R[i] // Copying sym.Reloc has measurable impact on performance
				if reloc.Type == objabi.R_DWARFSECREF && strings.HasPrefix(reloc.Sym.Name, dwarf.LocPrefix) {
					reloc.Sym.Attr |= sym.AttrReachable | sym.AttrNotInSymbolTable
					syms = append(syms, reloc.Sym)
					empty = false
					// LLVM doesn't support base address entries. Strip them out so LLDB and dsymutil don't get confused.
					if ctxt.HeadType == objabi.Hdarwin {
						removeDwarfAddrListBaseAddress(ctxt, fn, reloc.Sym, true)
					}
					// One location list entry per function, but many relocations to it. Don't duplicate.
					break
				}
			}
		}
	}
	// Don't emit .debug_loc if it's empty -- it makes the ARM linker mad.
	if !empty {
		locsym := ctxt.Syms.Lookup(".debug_loc", 0)
		locsym.Type = sym.SDWARFLOC
		locsym.Attr |= sym.AttrReachable
		syms = append(syms, locsym)
	}
	return syms
}

// removeDwarfAddrListBaseAddress removes base address selector entries from
// DWARF location lists and range lists.
func removeDwarfAddrListBaseAddress(ctxt *Link, info, list *sym.Symbol, isloclist bool) {
	// The list symbol contains multiple lists, but they're all for the
	// same function, and it's not empty.
	fn := list.R[0].Sym

	// Discard the relocations for the base address entries.
	list.R = list.R[:0]

	// Add relocations for each location entry's start and end addresses,
	// so that the base address entries aren't necessary.
	// We could remove them entirely, but that's more work for a relatively
	// small size win. If dsymutil runs it'll throw them away anyway.

	// relocate adds a CU-relative relocation to fn+addr at offset.
	relocate := func(addr uint64, offset int) {
		list.R = append(list.R, sym.Reloc{
			Off:  int32(offset),
			Siz:  uint8(ctxt.Arch.PtrSize),
			Type: objabi.R_ADDRCUOFF,
			Add:  int64(addr),
			Sym:  fn,
		})
	}

	for i := 0; i < len(list.P); {
		first := readPtr(ctxt, list.P[i:])
		second := readPtr(ctxt, list.P[i+ctxt.Arch.PtrSize:])

		if (first == 0 && second == 0) ||
			first == ^uint64(0) ||
			(ctxt.Arch.PtrSize == 4 && first == uint64(^uint32(0))) {
			// Base address selection entry or end of list. Ignore.
			i += ctxt.Arch.PtrSize * 2
			continue
		}

		relocate(first, i)
		relocate(second, i+ctxt.Arch.PtrSize)

		// Skip past the actual location.
		i += ctxt.Arch.PtrSize * 2
		if isloclist {
			i += 2 + int(ctxt.Arch.ByteOrder.Uint16(list.P[i:]))
		}
	}

	// Rewrite the DIE's relocations to point to the first location entry,
	// not the now-useless base address selection entry.
	for i := range info.R {
		r := &info.R[i]
		if r.Sym != list {
			continue
		}
		r.Add += int64(2 * ctxt.Arch.PtrSize)
	}
}

// Read a pointer-sized uint from the beginning of buf.
func readPtr(ctxt *Link, buf []byte) uint64 {
	switch ctxt.Arch.PtrSize {
	case 4:
		return uint64(ctxt.Arch.ByteOrder.Uint32(buf))
	case 8:
		return ctxt.Arch.ByteOrder.Uint64(buf)
	default:
		panic("unexpected pointer size")
	}
}

/*
 *  Elf.
 */
func dwarfaddshstrings(ctxt *Link, shstrtab *sym.Symbol) {
	if *FlagW { // disable dwarf
		return
	}

	secs := []string{"abbrev", "frame", "info", "loc", "line", "pubnames", "pubtypes", "gdb_scripts", "ranges"}
	for _, sec := range secs {
		Addstring(shstrtab, ".debug_"+sec)
		if ctxt.LinkMode == LinkExternal {
			Addstring(shstrtab, elfRelType+".debug_"+sec)
		} else {
			Addstring(shstrtab, ".zdebug_"+sec)
		}
	}
}

// Add section symbols for DWARF debug info.  This is called before
// dwarfaddelfheaders.
func dwarfaddelfsectionsyms(ctxt *Link) {
	if *FlagW { // disable dwarf
		return
	}
	if ctxt.LinkMode != LinkExternal {
		return
	}

	s := ctxt.Syms.Lookup(".debug_info", 0)
	putelfsectionsym(ctxt.Out, s, s.Sect.Elfsect.(*ElfShdr).shnum)
	s = ctxt.Syms.Lookup(".debug_abbrev", 0)
	putelfsectionsym(ctxt.Out, s, s.Sect.Elfsect.(*ElfShdr).shnum)
	s = ctxt.Syms.Lookup(".debug_line", 0)
	putelfsectionsym(ctxt.Out, s, s.Sect.Elfsect.(*ElfShdr).shnum)
	s = ctxt.Syms.Lookup(".debug_frame", 0)
	putelfsectionsym(ctxt.Out, s, s.Sect.Elfsect.(*ElfShdr).shnum)
	s = ctxt.Syms.Lookup(".debug_loc", 0)
	if s.Sect != nil {
		putelfsectionsym(ctxt.Out, s, s.Sect.Elfsect.(*ElfShdr).shnum)
	}
	s = ctxt.Syms.Lookup(".debug_ranges", 0)
	if s.Sect != nil {
		putelfsectionsym(ctxt.Out, s, s.Sect.Elfsect.(*ElfShdr).shnum)
	}
}

// dwarfcompress compresses the DWARF sections. This must happen after
// relocations are applied. After this, dwarfp will contain a
// different (new) set of symbols, and sections may have been replaced.
func dwarfcompress(ctxt *Link) {
	supported := ctxt.IsELF || ctxt.HeadType == objabi.Hwindows || ctxt.HeadType == objabi.Hdarwin
	if !ctxt.compressDWARF || !supported || ctxt.LinkMode != LinkInternal {
		return
	}

	var start int
	var newDwarfp []*sym.Symbol
	Segdwarf.Sections = Segdwarf.Sections[:0]
	for i, s := range dwarfp {
		// Find the boundaries between sections and compress
		// the whole section once we've found the last of its
		// symbols.
		if i+1 >= len(dwarfp) || s.Sect != dwarfp[i+1].Sect {
			s1 := compressSyms(ctxt, dwarfp[start:i+1])
			if s1 == nil {
				// Compression didn't help.
				newDwarfp = append(newDwarfp, dwarfp[start:i+1]...)
				Segdwarf.Sections = append(Segdwarf.Sections, s.Sect)
			} else {
				compressedSegName := ".zdebug_" + s.Sect.Name[len(".debug_"):]
				sect := addsection(ctxt.Arch, &Segdwarf, compressedSegName, 04)
				sect.Length = uint64(len(s1))
				newSym := ctxt.Syms.Lookup(compressedSegName, 0)
				newSym.P = s1
				newSym.Size = int64(len(s1))
				newSym.Sect = sect
				newDwarfp = append(newDwarfp, newSym)
			}
			start = i + 1
		}
	}
	dwarfp = newDwarfp

	// Re-compute the locations of the compressed DWARF symbols
	// and sections, since the layout of these within the file is
	// based on Section.Vaddr and Symbol.Value.
	pos := Segdwarf.Vaddr
	var prevSect *sym.Section
	for _, s := range dwarfp {
		s.Value = int64(pos)
		if s.Sect != prevSect {
			s.Sect.Vaddr = uint64(s.Value)
			prevSect = s.Sect
		}
		if s.Sub != nil {
			log.Fatalf("%s: unexpected sub-symbols", s)
		}
		pos += uint64(s.Size)
		if ctxt.HeadType == objabi.Hwindows {
			pos = uint64(Rnd(int64(pos), PEFILEALIGN))
		}

	}
	Segdwarf.Length = pos - Segdwarf.Vaddr
}

type compilationUnitByStartPC []*compilationUnit

func (v compilationUnitByStartPC) Len() int      { return len(v) }
func (v compilationUnitByStartPC) Swap(i, j int) { v[i], v[j] = v[j], v[i] }

func (v compilationUnitByStartPC) Less(i, j int) bool {
	switch {
	case len(v[i].lib.Textp) == 0 && len(v[j].lib.Textp) == 0:
		return v[i].lib.Pkg < v[j].lib.Pkg
	case len(v[i].lib.Textp) != 0 && len(v[j].lib.Textp) == 0:
		return true
	case len(v[i].lib.Textp) == 0 && len(v[j].lib.Textp) != 0:
		return false
	default:
		return v[i].lib.Textp[0].Value < v[j].lib.Textp[0].Value
	}
}

// On AIX, the symbol table needs to know where are the compilation units parts
// for a specific package in each .dw section.
// dwsectCUSize map will save the size of a compilation unit for
// the corresponding .dw section.
// This size can later be retrieved with the index "sectionName.pkgName".
var dwsectCUSize map[string]uint64

// getDwsectCUSize retrieves the corresponding package size inside the current section.
func getDwsectCUSize(sname string, pkgname string) uint64 {
	return dwsectCUSize[sname+"."+pkgname]
}

func saveDwsectCUSize(sname string, pkgname string, size uint64) {
	dwsectCUSize[sname+"."+pkgname] = size
}

// getPkgFromCUSym returns the package name for the compilation unit
// represented by s.
// The prefix dwarf.InfoPrefix+".pkg." needs to be removed in order to get
// the package name.
func getPkgFromCUSym(s *sym.Symbol) string {
	return strings.TrimPrefix(s.Name, dwarf.InfoPrefix+".pkg.")
}