File: gdb-jit.cc

package info (click to toggle)
nodejs 4.8.2~dfsg-1
  • links: PTS, VCS
  • area: main
  • in suites: stretch
  • size: 62,476 kB
  • ctags: 111,183
  • sloc: cpp: 661,544; ansic: 31,406; python: 23,073; makefile: 1,418; sh: 1,384; perl: 255; lisp: 222; ruby: 76; xml: 50
file content (2188 lines) | stat: -rw-r--r-- 63,593 bytes parent folder | download | duplicates (3)
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
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
// Copyright 2010 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "src/v8.h"

#include "src/base/bits.h"
#include "src/base/platform/platform.h"
#include "src/bootstrapper.h"
#include "src/compiler.h"
#include "src/frames-inl.h"
#include "src/frames.h"
#include "src/gdb-jit.h"
#include "src/global-handles.h"
#include "src/messages.h"
#include "src/objects.h"
#include "src/ostreams.h"
#include "src/snapshot/natives.h"

namespace v8 {
namespace internal {
namespace GDBJITInterface {

#ifdef ENABLE_GDB_JIT_INTERFACE

#ifdef __APPLE__
#define __MACH_O
class MachO;
class MachOSection;
typedef MachO DebugObject;
typedef MachOSection DebugSection;
#else
#define __ELF
class ELF;
class ELFSection;
typedef ELF DebugObject;
typedef ELFSection DebugSection;
#endif

class Writer BASE_EMBEDDED {
 public:
  explicit Writer(DebugObject* debug_object)
      : debug_object_(debug_object),
        position_(0),
        capacity_(1024),
        buffer_(reinterpret_cast<byte*>(malloc(capacity_))) {
  }

  ~Writer() {
    free(buffer_);
  }

  uintptr_t position() const {
    return position_;
  }

  template<typename T>
  class Slot {
   public:
    Slot(Writer* w, uintptr_t offset) : w_(w), offset_(offset) { }

    T* operator-> () {
      return w_->RawSlotAt<T>(offset_);
    }

    void set(const T& value) {
      *w_->RawSlotAt<T>(offset_) = value;
    }

    Slot<T> at(int i) {
      return Slot<T>(w_, offset_ + sizeof(T) * i);
    }

   private:
    Writer* w_;
    uintptr_t offset_;
  };

  template<typename T>
  void Write(const T& val) {
    Ensure(position_ + sizeof(T));
    *RawSlotAt<T>(position_) = val;
    position_ += sizeof(T);
  }

  template<typename T>
  Slot<T> SlotAt(uintptr_t offset) {
    Ensure(offset + sizeof(T));
    return Slot<T>(this, offset);
  }

  template<typename T>
  Slot<T> CreateSlotHere() {
    return CreateSlotsHere<T>(1);
  }

  template<typename T>
  Slot<T> CreateSlotsHere(uint32_t count) {
    uintptr_t slot_position = position_;
    position_ += sizeof(T) * count;
    Ensure(position_);
    return SlotAt<T>(slot_position);
  }

  void Ensure(uintptr_t pos) {
    if (capacity_ < pos) {
      while (capacity_ < pos) capacity_ *= 2;
      buffer_ = reinterpret_cast<byte*>(realloc(buffer_, capacity_));
    }
  }

  DebugObject* debug_object() { return debug_object_; }

  byte* buffer() { return buffer_; }

  void Align(uintptr_t align) {
    uintptr_t delta = position_ % align;
    if (delta == 0) return;
    uintptr_t padding = align - delta;
    Ensure(position_ += padding);
    DCHECK((position_ % align) == 0);
  }

  void WriteULEB128(uintptr_t value) {
    do {
      uint8_t byte = value & 0x7F;
      value >>= 7;
      if (value != 0) byte |= 0x80;
      Write<uint8_t>(byte);
    } while (value != 0);
  }

  void WriteSLEB128(intptr_t value) {
    bool more = true;
    while (more) {
      int8_t byte = value & 0x7F;
      bool byte_sign = byte & 0x40;
      value >>= 7;

      if ((value == 0 && !byte_sign) || (value == -1 && byte_sign)) {
        more = false;
      } else {
        byte |= 0x80;
      }

      Write<int8_t>(byte);
    }
  }

  void WriteString(const char* str) {
    do {
      Write<char>(*str);
    } while (*str++);
  }

 private:
  template<typename T> friend class Slot;

  template<typename T>
  T* RawSlotAt(uintptr_t offset) {
    DCHECK(offset < capacity_ && offset + sizeof(T) <= capacity_);
    return reinterpret_cast<T*>(&buffer_[offset]);
  }

  DebugObject* debug_object_;
  uintptr_t position_;
  uintptr_t capacity_;
  byte* buffer_;
};

class ELFStringTable;

template<typename THeader>
class DebugSectionBase : public ZoneObject {
 public:
  virtual ~DebugSectionBase() { }

  virtual void WriteBody(Writer::Slot<THeader> header, Writer* writer) {
    uintptr_t start = writer->position();
    if (WriteBodyInternal(writer)) {
      uintptr_t end = writer->position();
      header->offset = static_cast<uint32_t>(start);
#if defined(__MACH_O)
      header->addr = 0;
#endif
      header->size = end - start;
    }
  }

  virtual bool WriteBodyInternal(Writer* writer) {
    return false;
  }

  typedef THeader Header;
};


struct MachOSectionHeader {
  char sectname[16];
  char segname[16];
#if V8_TARGET_ARCH_IA32 || V8_TARGET_ARCH_X87
  uint32_t addr;
  uint32_t size;
#else
  uint64_t addr;
  uint64_t size;
#endif
  uint32_t offset;
  uint32_t align;
  uint32_t reloff;
  uint32_t nreloc;
  uint32_t flags;
  uint32_t reserved1;
  uint32_t reserved2;
};


class MachOSection : public DebugSectionBase<MachOSectionHeader> {
 public:
  enum Type {
    S_REGULAR = 0x0u,
    S_ATTR_COALESCED = 0xbu,
    S_ATTR_SOME_INSTRUCTIONS = 0x400u,
    S_ATTR_DEBUG = 0x02000000u,
    S_ATTR_PURE_INSTRUCTIONS = 0x80000000u
  };

  MachOSection(const char* name, const char* segment, uint32_t align,
               uint32_t flags)
      : name_(name), segment_(segment), align_(align), flags_(flags) {
    if (align_ != 0) {
      DCHECK(base::bits::IsPowerOfTwo32(align));
      align_ = WhichPowerOf2(align_);
    }
  }

  virtual ~MachOSection() { }

  virtual void PopulateHeader(Writer::Slot<Header> header) {
    header->addr = 0;
    header->size = 0;
    header->offset = 0;
    header->align = align_;
    header->reloff = 0;
    header->nreloc = 0;
    header->flags = flags_;
    header->reserved1 = 0;
    header->reserved2 = 0;
    memset(header->sectname, 0, sizeof(header->sectname));
    memset(header->segname, 0, sizeof(header->segname));
    DCHECK(strlen(name_) < sizeof(header->sectname));
    DCHECK(strlen(segment_) < sizeof(header->segname));
    strncpy(header->sectname, name_, sizeof(header->sectname));
    strncpy(header->segname, segment_, sizeof(header->segname));
  }

 private:
  const char* name_;
  const char* segment_;
  uint32_t align_;
  uint32_t flags_;
};


struct ELFSectionHeader {
  uint32_t name;
  uint32_t type;
  uintptr_t flags;
  uintptr_t address;
  uintptr_t offset;
  uintptr_t size;
  uint32_t link;
  uint32_t info;
  uintptr_t alignment;
  uintptr_t entry_size;
};


#if defined(__ELF)
class ELFSection : public DebugSectionBase<ELFSectionHeader> {
 public:
  enum Type {
    TYPE_NULL = 0,
    TYPE_PROGBITS = 1,
    TYPE_SYMTAB = 2,
    TYPE_STRTAB = 3,
    TYPE_RELA = 4,
    TYPE_HASH = 5,
    TYPE_DYNAMIC = 6,
    TYPE_NOTE = 7,
    TYPE_NOBITS = 8,
    TYPE_REL = 9,
    TYPE_SHLIB = 10,
    TYPE_DYNSYM = 11,
    TYPE_LOPROC = 0x70000000,
    TYPE_X86_64_UNWIND = 0x70000001,
    TYPE_HIPROC = 0x7fffffff,
    TYPE_LOUSER = 0x80000000,
    TYPE_HIUSER = 0xffffffff
  };

  enum Flags {
    FLAG_WRITE = 1,
    FLAG_ALLOC = 2,
    FLAG_EXEC = 4
  };

  enum SpecialIndexes {
    INDEX_ABSOLUTE = 0xfff1
  };

  ELFSection(const char* name, Type type, uintptr_t align)
      : name_(name), type_(type), align_(align) { }

  virtual ~ELFSection() { }

  void PopulateHeader(Writer::Slot<Header> header, ELFStringTable* strtab);

  virtual void WriteBody(Writer::Slot<Header> header, Writer* w) {
    uintptr_t start = w->position();
    if (WriteBodyInternal(w)) {
      uintptr_t end = w->position();
      header->offset = start;
      header->size = end - start;
    }
  }

  virtual bool WriteBodyInternal(Writer* w) {
    return false;
  }

  uint16_t index() const { return index_; }
  void set_index(uint16_t index) { index_ = index; }

 protected:
  virtual void PopulateHeader(Writer::Slot<Header> header) {
    header->flags = 0;
    header->address = 0;
    header->offset = 0;
    header->size = 0;
    header->link = 0;
    header->info = 0;
    header->entry_size = 0;
  }

 private:
  const char* name_;
  Type type_;
  uintptr_t align_;
  uint16_t index_;
};
#endif  // defined(__ELF)


#if defined(__MACH_O)
class MachOTextSection : public MachOSection {
 public:
  MachOTextSection(uintptr_t align,
                   uintptr_t addr,
                   uintptr_t size)
      : MachOSection("__text",
                     "__TEXT",
                     align,
                     MachOSection::S_REGULAR |
                         MachOSection::S_ATTR_SOME_INSTRUCTIONS |
                         MachOSection::S_ATTR_PURE_INSTRUCTIONS),
        addr_(addr),
        size_(size) { }

 protected:
  virtual void PopulateHeader(Writer::Slot<Header> header) {
    MachOSection::PopulateHeader(header);
    header->addr = addr_;
    header->size = size_;
  }

 private:
  uintptr_t addr_;
  uintptr_t size_;
};
#endif  // defined(__MACH_O)


#if defined(__ELF)
class FullHeaderELFSection : public ELFSection {
 public:
  FullHeaderELFSection(const char* name,
                       Type type,
                       uintptr_t align,
                       uintptr_t addr,
                       uintptr_t offset,
                       uintptr_t size,
                       uintptr_t flags)
      : ELFSection(name, type, align),
        addr_(addr),
        offset_(offset),
        size_(size),
        flags_(flags) { }

 protected:
  virtual void PopulateHeader(Writer::Slot<Header> header) {
    ELFSection::PopulateHeader(header);
    header->address = addr_;
    header->offset = offset_;
    header->size = size_;
    header->flags = flags_;
  }

 private:
  uintptr_t addr_;
  uintptr_t offset_;
  uintptr_t size_;
  uintptr_t flags_;
};


class ELFStringTable : public ELFSection {
 public:
  explicit ELFStringTable(const char* name)
      : ELFSection(name, TYPE_STRTAB, 1), writer_(NULL), offset_(0), size_(0) {
  }

  uintptr_t Add(const char* str) {
    if (*str == '\0') return 0;

    uintptr_t offset = size_;
    WriteString(str);
    return offset;
  }

  void AttachWriter(Writer* w) {
    writer_ = w;
    offset_ = writer_->position();

    // First entry in the string table should be an empty string.
    WriteString("");
  }

  void DetachWriter() {
    writer_ = NULL;
  }

  virtual void WriteBody(Writer::Slot<Header> header, Writer* w) {
    DCHECK(writer_ == NULL);
    header->offset = offset_;
    header->size = size_;
  }

 private:
  void WriteString(const char* str) {
    uintptr_t written = 0;
    do {
      writer_->Write(*str);
      written++;
    } while (*str++);
    size_ += written;
  }

  Writer* writer_;

  uintptr_t offset_;
  uintptr_t size_;
};


void ELFSection::PopulateHeader(Writer::Slot<ELFSection::Header> header,
                                ELFStringTable* strtab) {
  header->name = static_cast<uint32_t>(strtab->Add(name_));
  header->type = type_;
  header->alignment = align_;
  PopulateHeader(header);
}
#endif  // defined(__ELF)


#if defined(__MACH_O)
class MachO BASE_EMBEDDED {
 public:
  explicit MachO(Zone* zone) : zone_(zone), sections_(6, zone) { }

  uint32_t AddSection(MachOSection* section) {
    sections_.Add(section, zone_);
    return sections_.length() - 1;
  }

  void Write(Writer* w, uintptr_t code_start, uintptr_t code_size) {
    Writer::Slot<MachOHeader> header = WriteHeader(w);
    uintptr_t load_command_start = w->position();
    Writer::Slot<MachOSegmentCommand> cmd = WriteSegmentCommand(w,
                                                                code_start,
                                                                code_size);
    WriteSections(w, cmd, header, load_command_start);
  }

 private:
  struct MachOHeader {
    uint32_t magic;
    uint32_t cputype;
    uint32_t cpusubtype;
    uint32_t filetype;
    uint32_t ncmds;
    uint32_t sizeofcmds;
    uint32_t flags;
#if V8_TARGET_ARCH_X64
    uint32_t reserved;
#endif
  };

  struct MachOSegmentCommand {
    uint32_t cmd;
    uint32_t cmdsize;
    char segname[16];
#if V8_TARGET_ARCH_IA32 || V8_TARGET_ARCH_X87
    uint32_t vmaddr;
    uint32_t vmsize;
    uint32_t fileoff;
    uint32_t filesize;
#else
    uint64_t vmaddr;
    uint64_t vmsize;
    uint64_t fileoff;
    uint64_t filesize;
#endif
    uint32_t maxprot;
    uint32_t initprot;
    uint32_t nsects;
    uint32_t flags;
  };

  enum MachOLoadCommandCmd {
    LC_SEGMENT_32 = 0x00000001u,
    LC_SEGMENT_64 = 0x00000019u
  };


  Writer::Slot<MachOHeader> WriteHeader(Writer* w) {
    DCHECK(w->position() == 0);
    Writer::Slot<MachOHeader> header = w->CreateSlotHere<MachOHeader>();
#if V8_TARGET_ARCH_IA32 || V8_TARGET_ARCH_X87
    header->magic = 0xFEEDFACEu;
    header->cputype = 7;  // i386
    header->cpusubtype = 3;  // CPU_SUBTYPE_I386_ALL
#elif V8_TARGET_ARCH_X64
    header->magic = 0xFEEDFACFu;
    header->cputype = 7 | 0x01000000;  // i386 | 64-bit ABI
    header->cpusubtype = 3;  // CPU_SUBTYPE_I386_ALL
    header->reserved = 0;
#else
#error Unsupported target architecture.
#endif
    header->filetype = 0x1;  // MH_OBJECT
    header->ncmds = 1;
    header->sizeofcmds = 0;
    header->flags = 0;
    return header;
  }


  Writer::Slot<MachOSegmentCommand> WriteSegmentCommand(Writer* w,
                                                        uintptr_t code_start,
                                                        uintptr_t code_size) {
    Writer::Slot<MachOSegmentCommand> cmd =
        w->CreateSlotHere<MachOSegmentCommand>();
#if V8_TARGET_ARCH_IA32 || V8_TARGET_ARCH_X87
    cmd->cmd = LC_SEGMENT_32;
#else
    cmd->cmd = LC_SEGMENT_64;
#endif
    cmd->vmaddr = code_start;
    cmd->vmsize = code_size;
    cmd->fileoff = 0;
    cmd->filesize = 0;
    cmd->maxprot = 7;
    cmd->initprot = 7;
    cmd->flags = 0;
    cmd->nsects = sections_.length();
    memset(cmd->segname, 0, 16);
    cmd->cmdsize = sizeof(MachOSegmentCommand) + sizeof(MachOSection::Header) *
        cmd->nsects;
    return cmd;
  }


  void WriteSections(Writer* w,
                     Writer::Slot<MachOSegmentCommand> cmd,
                     Writer::Slot<MachOHeader> header,
                     uintptr_t load_command_start) {
    Writer::Slot<MachOSection::Header> headers =
        w->CreateSlotsHere<MachOSection::Header>(sections_.length());
    cmd->fileoff = w->position();
    header->sizeofcmds = w->position() - load_command_start;
    for (int section = 0; section < sections_.length(); ++section) {
      sections_[section]->PopulateHeader(headers.at(section));
      sections_[section]->WriteBody(headers.at(section), w);
    }
    cmd->filesize = w->position() - (uintptr_t)cmd->fileoff;
  }

  Zone* zone_;
  ZoneList<MachOSection*> sections_;
};
#endif  // defined(__MACH_O)


#if defined(__ELF)
class ELF BASE_EMBEDDED {
 public:
  explicit ELF(Zone* zone) : zone_(zone), sections_(6, zone) {
    sections_.Add(new(zone) ELFSection("", ELFSection::TYPE_NULL, 0), zone);
    sections_.Add(new(zone) ELFStringTable(".shstrtab"), zone);
  }

  void Write(Writer* w) {
    WriteHeader(w);
    WriteSectionTable(w);
    WriteSections(w);
  }

  ELFSection* SectionAt(uint32_t index) {
    return sections_[index];
  }

  uint32_t AddSection(ELFSection* section) {
    sections_.Add(section, zone_);
    section->set_index(sections_.length() - 1);
    return sections_.length() - 1;
  }

 private:
  struct ELFHeader {
    uint8_t ident[16];
    uint16_t type;
    uint16_t machine;
    uint32_t version;
    uintptr_t entry;
    uintptr_t pht_offset;
    uintptr_t sht_offset;
    uint32_t flags;
    uint16_t header_size;
    uint16_t pht_entry_size;
    uint16_t pht_entry_num;
    uint16_t sht_entry_size;
    uint16_t sht_entry_num;
    uint16_t sht_strtab_index;
  };


  void WriteHeader(Writer* w) {
    DCHECK(w->position() == 0);
    Writer::Slot<ELFHeader> header = w->CreateSlotHere<ELFHeader>();
#if (V8_TARGET_ARCH_IA32 || V8_TARGET_ARCH_ARM || V8_TARGET_ARCH_X87 || \
     (V8_TARGET_ARCH_X64 && V8_TARGET_ARCH_32_BIT))
    const uint8_t ident[16] =
        { 0x7f, 'E', 'L', 'F', 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0};
#elif V8_TARGET_ARCH_X64 && V8_TARGET_ARCH_64_BIT
    const uint8_t ident[16] =
        { 0x7f, 'E', 'L', 'F', 2, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0};
#elif defined(V8_TARGET_ARCH_S390) && V8_TARGET_ARCH_32_BIT
    const uint8_t ident[16] =
        { 0x7f, 'E', 'L', 'F', 1, 2, 1, 3, 0, 0, 0, 0, 0, 0, 0, 0};
#elif defined(V8_TARGET_ARCH_S390X)
     const uint8_t ident[16] =
        { 0x7f, 'E', 'L', 'F', 2, 2, 1, 3, 0, 0, 0, 0, 0, 0, 0, 0};
#else
#error Unsupported target architecture.
#endif
    memcpy(header->ident, ident, 16);
    header->type = 1;
#if V8_TARGET_ARCH_IA32 || V8_TARGET_ARCH_X87
    header->machine = 3;
#elif V8_TARGET_ARCH_X64
    // Processor identification value for x64 is 62 as defined in
    //    System V ABI, AMD64 Supplement
    //    http://www.x86-64.org/documentation/abi.pdf
    header->machine = 62;
#elif V8_TARGET_ARCH_ARM
    // Set to EM_ARM, defined as 40, in "ARM ELF File Format" at
    // infocenter.arm.com/help/topic/com.arm.doc.dui0101a/DUI0101A_Elf.pdf
    header->machine = 40;
#elif V8_TARGET_ARCH_S390
    // Processor identification value is 22 as defined in the System Z ABI,
    // under Object Files, ELF Header:
    // http://refspecs.linuxbase.org/ELF/zSeries/lzsabi0_zSeries.html#AEN1597
    header->machine = 22;
#else
#error Unsupported target architecture.
#endif
    header->version = 1;
    header->entry = 0;
    header->pht_offset = 0;
    header->sht_offset = sizeof(ELFHeader);  // Section table follows header.
    header->flags = 0;
    header->header_size = sizeof(ELFHeader);
    header->pht_entry_size = 0;
    header->pht_entry_num = 0;
    header->sht_entry_size = sizeof(ELFSection::Header);
    header->sht_entry_num = sections_.length();
    header->sht_strtab_index = 1;
  }

  void WriteSectionTable(Writer* w) {
    // Section headers table immediately follows file header.
    DCHECK(w->position() == sizeof(ELFHeader));

    Writer::Slot<ELFSection::Header> headers =
        w->CreateSlotsHere<ELFSection::Header>(sections_.length());

    // String table for section table is the first section.
    ELFStringTable* strtab = static_cast<ELFStringTable*>(SectionAt(1));
    strtab->AttachWriter(w);
    for (int i = 0, length = sections_.length();
         i < length;
         i++) {
      sections_[i]->PopulateHeader(headers.at(i), strtab);
    }
    strtab->DetachWriter();
  }

  int SectionHeaderPosition(uint32_t section_index) {
    return sizeof(ELFHeader) + sizeof(ELFSection::Header) * section_index;
  }

  void WriteSections(Writer* w) {
    Writer::Slot<ELFSection::Header> headers =
        w->SlotAt<ELFSection::Header>(sizeof(ELFHeader));

    for (int i = 0, length = sections_.length();
         i < length;
         i++) {
      sections_[i]->WriteBody(headers.at(i), w);
    }
  }

  Zone* zone_;
  ZoneList<ELFSection*> sections_;
};


class ELFSymbol BASE_EMBEDDED {
 public:
  enum Type {
    TYPE_NOTYPE = 0,
    TYPE_OBJECT = 1,
    TYPE_FUNC = 2,
    TYPE_SECTION = 3,
    TYPE_FILE = 4,
    TYPE_LOPROC = 13,
    TYPE_HIPROC = 15
  };

  enum Binding {
    BIND_LOCAL = 0,
    BIND_GLOBAL = 1,
    BIND_WEAK = 2,
    BIND_LOPROC = 13,
    BIND_HIPROC = 15
  };

  ELFSymbol(const char* name,
            uintptr_t value,
            uintptr_t size,
            Binding binding,
            Type type,
            uint16_t section)
      : name(name),
        value(value),
        size(size),
        info((binding << 4) | type),
        other(0),
        section(section) {
  }

  Binding binding() const {
    return static_cast<Binding>(info >> 4);
  }
#if (V8_TARGET_ARCH_IA32 || V8_TARGET_ARCH_ARM || V8_TARGET_ARCH_X87 || \
     (V8_TARGET_ARCH_X64 && V8_TARGET_ARCH_32_BIT) || \
     (V8_TARGET_ARCH_S390 && V8_TARGET_ARCH_32_BIT))
  struct SerializedLayout {
    SerializedLayout(uint32_t name,
                     uintptr_t value,
                     uintptr_t size,
                     Binding binding,
                     Type type,
                     uint16_t section)
        : name(name),
          value(value),
          size(size),
          info((binding << 4) | type),
          other(0),
          section(section) {
    }

    uint32_t name;
    uintptr_t value;
    uintptr_t size;
    uint8_t info;
    uint8_t other;
    uint16_t section;
  };
#elif V8_TARGET_ARCH_X64 && V8_TARGET_ARCH_64_BIT || \
      V8_TARGET_ARCH_S390X
  struct SerializedLayout {
    SerializedLayout(uint32_t name,
                     uintptr_t value,
                     uintptr_t size,
                     Binding binding,
                     Type type,
                     uint16_t section)
        : name(name),
          info((binding << 4) | type),
          other(0),
          section(section),
          value(value),
          size(size) {
    }

    uint32_t name;
    uint8_t info;
    uint8_t other;
    uint16_t section;
    uintptr_t value;
    uintptr_t size;
  };
#endif

  void Write(Writer::Slot<SerializedLayout> s, ELFStringTable* t) {
    // Convert symbol names from strings to indexes in the string table.
    s->name = static_cast<uint32_t>(t->Add(name));
    s->value = value;
    s->size = size;
    s->info = info;
    s->other = other;
    s->section = section;
  }

 private:
  const char* name;
  uintptr_t value;
  uintptr_t size;
  uint8_t info;
  uint8_t other;
  uint16_t section;
};


class ELFSymbolTable : public ELFSection {
 public:
  ELFSymbolTable(const char* name, Zone* zone)
      : ELFSection(name, TYPE_SYMTAB, sizeof(uintptr_t)),
        locals_(1, zone),
        globals_(1, zone) {
  }

  virtual void WriteBody(Writer::Slot<Header> header, Writer* w) {
    w->Align(header->alignment);
    int total_symbols = locals_.length() + globals_.length() + 1;
    header->offset = w->position();

    Writer::Slot<ELFSymbol::SerializedLayout> symbols =
        w->CreateSlotsHere<ELFSymbol::SerializedLayout>(total_symbols);

    header->size = w->position() - header->offset;

    // String table for this symbol table should follow it in the section table.
    ELFStringTable* strtab =
        static_cast<ELFStringTable*>(w->debug_object()->SectionAt(index() + 1));
    strtab->AttachWriter(w);
    symbols.at(0).set(ELFSymbol::SerializedLayout(0,
                                                  0,
                                                  0,
                                                  ELFSymbol::BIND_LOCAL,
                                                  ELFSymbol::TYPE_NOTYPE,
                                                  0));
    WriteSymbolsList(&locals_, symbols.at(1), strtab);
    WriteSymbolsList(&globals_, symbols.at(locals_.length() + 1), strtab);
    strtab->DetachWriter();
  }

  void Add(const ELFSymbol& symbol, Zone* zone) {
    if (symbol.binding() == ELFSymbol::BIND_LOCAL) {
      locals_.Add(symbol, zone);
    } else {
      globals_.Add(symbol, zone);
    }
  }

 protected:
  virtual void PopulateHeader(Writer::Slot<Header> header) {
    ELFSection::PopulateHeader(header);
    // We are assuming that string table will follow symbol table.
    header->link = index() + 1;
    header->info = locals_.length() + 1;
    header->entry_size = sizeof(ELFSymbol::SerializedLayout);
  }

 private:
  void WriteSymbolsList(const ZoneList<ELFSymbol>* src,
                        Writer::Slot<ELFSymbol::SerializedLayout> dst,
                        ELFStringTable* strtab) {
    for (int i = 0, len = src->length();
         i < len;
         i++) {
      src->at(i).Write(dst.at(i), strtab);
    }
  }

  ZoneList<ELFSymbol> locals_;
  ZoneList<ELFSymbol> globals_;
};
#endif  // defined(__ELF)


class LineInfo : public Malloced {
 public:
  LineInfo() : pc_info_(10) {}

  void SetPosition(intptr_t pc, int pos, bool is_statement) {
    AddPCInfo(PCInfo(pc, pos, is_statement));
  }

  struct PCInfo {
    PCInfo(intptr_t pc, int pos, bool is_statement)
        : pc_(pc), pos_(pos), is_statement_(is_statement) {}

    intptr_t pc_;
    int pos_;
    bool is_statement_;
  };

  List<PCInfo>* pc_info() { return &pc_info_; }

 private:
  void AddPCInfo(const PCInfo& pc_info) { pc_info_.Add(pc_info); }

  List<PCInfo> pc_info_;
};


class CodeDescription BASE_EMBEDDED {
 public:
#if V8_TARGET_ARCH_X64
  enum StackState {
    POST_RBP_PUSH,
    POST_RBP_SET,
    POST_RBP_POP,
    STACK_STATE_MAX
  };
#endif

  CodeDescription(const char* name, Code* code, SharedFunctionInfo* shared,
                  LineInfo* lineinfo)
      : name_(name), code_(code), shared_info_(shared), lineinfo_(lineinfo) {}

  const char* name() const {
    return name_;
  }

  LineInfo* lineinfo() const { return lineinfo_; }

  bool is_function() const {
    Code::Kind kind = code_->kind();
    return kind == Code::FUNCTION || kind == Code::OPTIMIZED_FUNCTION;
  }

  bool has_scope_info() const { return shared_info_ != NULL; }

  ScopeInfo* scope_info() const {
    DCHECK(has_scope_info());
    return shared_info_->scope_info();
  }

  uintptr_t CodeStart() const {
    return reinterpret_cast<uintptr_t>(code_->instruction_start());
  }

  uintptr_t CodeEnd() const {
    return reinterpret_cast<uintptr_t>(code_->instruction_end());
  }

  uintptr_t CodeSize() const {
    return CodeEnd() - CodeStart();
  }

  bool has_script() {
    return shared_info_ != NULL && shared_info_->script()->IsScript();
  }

  Script* script() { return Script::cast(shared_info_->script()); }

  bool IsLineInfoAvailable() {
    return has_script() && script()->source()->IsString() &&
           script()->HasValidSource() && script()->name()->IsString() &&
           lineinfo_ != NULL;
  }

#if V8_TARGET_ARCH_X64
  uintptr_t GetStackStateStartAddress(StackState state) const {
    DCHECK(state < STACK_STATE_MAX);
    return stack_state_start_addresses_[state];
  }

  void SetStackStateStartAddress(StackState state, uintptr_t addr) {
    DCHECK(state < STACK_STATE_MAX);
    stack_state_start_addresses_[state] = addr;
  }
#endif

  SmartArrayPointer<char> GetFilename() {
    return String::cast(script()->name())->ToCString();
  }

  int GetScriptLineNumber(int pos) { return script()->GetLineNumber(pos) + 1; }


 private:
  const char* name_;
  Code* code_;
  SharedFunctionInfo* shared_info_;
  LineInfo* lineinfo_;
#if V8_TARGET_ARCH_X64
  uintptr_t stack_state_start_addresses_[STACK_STATE_MAX];
#endif
};

#if defined(__ELF)
static void CreateSymbolsTable(CodeDescription* desc,
                               Zone* zone,
                               ELF* elf,
                               int text_section_index) {
  ELFSymbolTable* symtab = new(zone) ELFSymbolTable(".symtab", zone);
  ELFStringTable* strtab = new(zone) ELFStringTable(".strtab");

  // Symbol table should be followed by the linked string table.
  elf->AddSection(symtab);
  elf->AddSection(strtab);

  symtab->Add(ELFSymbol("V8 Code",
                        0,
                        0,
                        ELFSymbol::BIND_LOCAL,
                        ELFSymbol::TYPE_FILE,
                        ELFSection::INDEX_ABSOLUTE),
              zone);

  symtab->Add(ELFSymbol(desc->name(),
                        0,
                        desc->CodeSize(),
                        ELFSymbol::BIND_GLOBAL,
                        ELFSymbol::TYPE_FUNC,
                        text_section_index),
              zone);
}
#endif  // defined(__ELF)


class DebugInfoSection : public DebugSection {
 public:
  explicit DebugInfoSection(CodeDescription* desc)
#if defined(__ELF)
      : ELFSection(".debug_info", TYPE_PROGBITS, 1),
#else
      : MachOSection("__debug_info",
                     "__DWARF",
                     1,
                     MachOSection::S_REGULAR | MachOSection::S_ATTR_DEBUG),
#endif
        desc_(desc) { }

  // DWARF2 standard
  enum DWARF2LocationOp {
    DW_OP_reg0 = 0x50,
    DW_OP_reg1 = 0x51,
    DW_OP_reg2 = 0x52,
    DW_OP_reg3 = 0x53,
    DW_OP_reg4 = 0x54,
    DW_OP_reg5 = 0x55,
    DW_OP_reg6 = 0x56,
    DW_OP_reg7 = 0x57,
    DW_OP_reg8 = 0x58,
    DW_OP_reg9 = 0x59,
    DW_OP_reg10 = 0x5a,
    DW_OP_reg11 = 0x5b,
    DW_OP_fbreg = 0x91  // 1 param: SLEB128 offset
  };

  enum DWARF2Encoding {
    DW_ATE_ADDRESS = 0x1,
    DW_ATE_SIGNED = 0x5
  };

  bool WriteBodyInternal(Writer* w) {
    uintptr_t cu_start = w->position();
    Writer::Slot<uint32_t> size = w->CreateSlotHere<uint32_t>();
    uintptr_t start = w->position();
    w->Write<uint16_t>(2);  // DWARF version.
    w->Write<uint32_t>(0);  // Abbreviation table offset.
    w->Write<uint8_t>(sizeof(intptr_t));

    w->WriteULEB128(1);  // Abbreviation code.
    w->WriteString(desc_->GetFilename().get());
    w->Write<intptr_t>(desc_->CodeStart());
    w->Write<intptr_t>(desc_->CodeStart() + desc_->CodeSize());
    w->Write<uint32_t>(0);

    uint32_t ty_offset = static_cast<uint32_t>(w->position() - cu_start);
    w->WriteULEB128(3);
    w->Write<uint8_t>(kPointerSize);
    w->WriteString("v8value");

    if (desc_->has_scope_info()) {
      ScopeInfo* scope = desc_->scope_info();
      w->WriteULEB128(2);
      w->WriteString(desc_->name());
      w->Write<intptr_t>(desc_->CodeStart());
      w->Write<intptr_t>(desc_->CodeStart() + desc_->CodeSize());
      Writer::Slot<uint32_t> fb_block_size = w->CreateSlotHere<uint32_t>();
      uintptr_t fb_block_start = w->position();
#if V8_TARGET_ARCH_IA32 || V8_TARGET_ARCH_X87
      w->Write<uint8_t>(DW_OP_reg5);  // The frame pointer's here on ia32
#elif V8_TARGET_ARCH_X64
      w->Write<uint8_t>(DW_OP_reg6);  // and here on x64.
#elif V8_TARGET_ARCH_ARM
      UNIMPLEMENTED();
#elif V8_TARGET_ARCH_MIPS
      UNIMPLEMENTED();
#elif V8_TARGET_ARCH_MIPS64
      UNIMPLEMENTED();
#elif V8_TARGET_ARCH_S390
      w->Write<uint8_t>(DW_OP_reg11);  // The frame pointer's here on s390
#else
#error Unsupported target architecture.
#endif
      fb_block_size.set(static_cast<uint32_t>(w->position() - fb_block_start));

      int params = scope->ParameterCount();
      int slots = scope->StackLocalCount();
      int context_slots = scope->ContextLocalCount();
      // The real slot ID is internal_slots + context_slot_id.
      int internal_slots = Context::MIN_CONTEXT_SLOTS;
      int locals = scope->StackLocalCount();
      int current_abbreviation = 4;

      for (int param = 0; param < params; ++param) {
        w->WriteULEB128(current_abbreviation++);
        w->WriteString(
            scope->ParameterName(param)->ToCString(DISALLOW_NULLS).get());
        w->Write<uint32_t>(ty_offset);
        Writer::Slot<uint32_t> block_size = w->CreateSlotHere<uint32_t>();
        uintptr_t block_start = w->position();
        w->Write<uint8_t>(DW_OP_fbreg);
        w->WriteSLEB128(
          JavaScriptFrameConstants::kLastParameterOffset +
              kPointerSize * (params - param - 1));
        block_size.set(static_cast<uint32_t>(w->position() - block_start));
      }

      EmbeddedVector<char, 256> buffer;
      StringBuilder builder(buffer.start(), buffer.length());

      for (int slot = 0; slot < slots; ++slot) {
        w->WriteULEB128(current_abbreviation++);
        builder.Reset();
        builder.AddFormatted("slot%d", slot);
        w->WriteString(builder.Finalize());
      }

      // See contexts.h for more information.
      DCHECK(Context::MIN_CONTEXT_SLOTS == 4);
      DCHECK(Context::CLOSURE_INDEX == 0);
      DCHECK(Context::PREVIOUS_INDEX == 1);
      DCHECK(Context::EXTENSION_INDEX == 2);
      DCHECK(Context::GLOBAL_OBJECT_INDEX == 3);
      w->WriteULEB128(current_abbreviation++);
      w->WriteString(".closure");
      w->WriteULEB128(current_abbreviation++);
      w->WriteString(".previous");
      w->WriteULEB128(current_abbreviation++);
      w->WriteString(".extension");
      w->WriteULEB128(current_abbreviation++);
      w->WriteString(".global");

      for (int context_slot = 0;
           context_slot < context_slots;
           ++context_slot) {
        w->WriteULEB128(current_abbreviation++);
        builder.Reset();
        builder.AddFormatted("context_slot%d", context_slot + internal_slots);
        w->WriteString(builder.Finalize());
      }

      for (int local = 0; local < locals; ++local) {
        w->WriteULEB128(current_abbreviation++);
        w->WriteString(
            scope->StackLocalName(local)->ToCString(DISALLOW_NULLS).get());
        w->Write<uint32_t>(ty_offset);
        Writer::Slot<uint32_t> block_size = w->CreateSlotHere<uint32_t>();
        uintptr_t block_start = w->position();
        w->Write<uint8_t>(DW_OP_fbreg);
        w->WriteSLEB128(
          JavaScriptFrameConstants::kLocal0Offset -
              kPointerSize * local);
        block_size.set(static_cast<uint32_t>(w->position() - block_start));
      }

      {
        w->WriteULEB128(current_abbreviation++);
        w->WriteString("__function");
        w->Write<uint32_t>(ty_offset);
        Writer::Slot<uint32_t> block_size = w->CreateSlotHere<uint32_t>();
        uintptr_t block_start = w->position();
        w->Write<uint8_t>(DW_OP_fbreg);
        w->WriteSLEB128(JavaScriptFrameConstants::kFunctionOffset);
        block_size.set(static_cast<uint32_t>(w->position() - block_start));
      }

      {
        w->WriteULEB128(current_abbreviation++);
        w->WriteString("__context");
        w->Write<uint32_t>(ty_offset);
        Writer::Slot<uint32_t> block_size = w->CreateSlotHere<uint32_t>();
        uintptr_t block_start = w->position();
        w->Write<uint8_t>(DW_OP_fbreg);
        w->WriteSLEB128(StandardFrameConstants::kContextOffset);
        block_size.set(static_cast<uint32_t>(w->position() - block_start));
      }

      w->WriteULEB128(0);  // Terminate the sub program.
    }

    w->WriteULEB128(0);  // Terminate the compile unit.
    size.set(static_cast<uint32_t>(w->position() - start));
    return true;
  }

 private:
  CodeDescription* desc_;
};


class DebugAbbrevSection : public DebugSection {
 public:
  explicit DebugAbbrevSection(CodeDescription* desc)
#ifdef __ELF
      : ELFSection(".debug_abbrev", TYPE_PROGBITS, 1),
#else
      : MachOSection("__debug_abbrev",
                     "__DWARF",
                     1,
                     MachOSection::S_REGULAR | MachOSection::S_ATTR_DEBUG),
#endif
        desc_(desc) { }

  // DWARF2 standard, figure 14.
  enum DWARF2Tags {
    DW_TAG_FORMAL_PARAMETER = 0x05,
    DW_TAG_POINTER_TYPE = 0xf,
    DW_TAG_COMPILE_UNIT = 0x11,
    DW_TAG_STRUCTURE_TYPE = 0x13,
    DW_TAG_BASE_TYPE = 0x24,
    DW_TAG_SUBPROGRAM = 0x2e,
    DW_TAG_VARIABLE = 0x34
  };

  // DWARF2 standard, figure 16.
  enum DWARF2ChildrenDetermination {
    DW_CHILDREN_NO = 0,
    DW_CHILDREN_YES = 1
  };

  // DWARF standard, figure 17.
  enum DWARF2Attribute {
    DW_AT_LOCATION = 0x2,
    DW_AT_NAME = 0x3,
    DW_AT_BYTE_SIZE = 0xb,
    DW_AT_STMT_LIST = 0x10,
    DW_AT_LOW_PC = 0x11,
    DW_AT_HIGH_PC = 0x12,
    DW_AT_ENCODING = 0x3e,
    DW_AT_FRAME_BASE = 0x40,
    DW_AT_TYPE = 0x49
  };

  // DWARF2 standard, figure 19.
  enum DWARF2AttributeForm {
    DW_FORM_ADDR = 0x1,
    DW_FORM_BLOCK4 = 0x4,
    DW_FORM_STRING = 0x8,
    DW_FORM_DATA4 = 0x6,
    DW_FORM_BLOCK = 0x9,
    DW_FORM_DATA1 = 0xb,
    DW_FORM_FLAG = 0xc,
    DW_FORM_REF4 = 0x13
  };

  void WriteVariableAbbreviation(Writer* w,
                                 int abbreviation_code,
                                 bool has_value,
                                 bool is_parameter) {
    w->WriteULEB128(abbreviation_code);
    w->WriteULEB128(is_parameter ? DW_TAG_FORMAL_PARAMETER : DW_TAG_VARIABLE);
    w->Write<uint8_t>(DW_CHILDREN_NO);
    w->WriteULEB128(DW_AT_NAME);
    w->WriteULEB128(DW_FORM_STRING);
    if (has_value) {
      w->WriteULEB128(DW_AT_TYPE);
      w->WriteULEB128(DW_FORM_REF4);
      w->WriteULEB128(DW_AT_LOCATION);
      w->WriteULEB128(DW_FORM_BLOCK4);
    }
    w->WriteULEB128(0);
    w->WriteULEB128(0);
  }

  bool WriteBodyInternal(Writer* w) {
    int current_abbreviation = 1;
    bool extra_info = desc_->has_scope_info();
    DCHECK(desc_->IsLineInfoAvailable());
    w->WriteULEB128(current_abbreviation++);
    w->WriteULEB128(DW_TAG_COMPILE_UNIT);
    w->Write<uint8_t>(extra_info ? DW_CHILDREN_YES : DW_CHILDREN_NO);
    w->WriteULEB128(DW_AT_NAME);
    w->WriteULEB128(DW_FORM_STRING);
    w->WriteULEB128(DW_AT_LOW_PC);
    w->WriteULEB128(DW_FORM_ADDR);
    w->WriteULEB128(DW_AT_HIGH_PC);
    w->WriteULEB128(DW_FORM_ADDR);
    w->WriteULEB128(DW_AT_STMT_LIST);
    w->WriteULEB128(DW_FORM_DATA4);
    w->WriteULEB128(0);
    w->WriteULEB128(0);

    if (extra_info) {
      ScopeInfo* scope = desc_->scope_info();
      int params = scope->ParameterCount();
      int slots = scope->StackLocalCount();
      int context_slots = scope->ContextLocalCount();
      // The real slot ID is internal_slots + context_slot_id.
      int internal_slots = Context::MIN_CONTEXT_SLOTS;
      int locals = scope->StackLocalCount();
      // Total children is params + slots + context_slots + internal_slots +
      // locals + 2 (__function and __context).

      // The extra duplication below seems to be necessary to keep
      // gdb from getting upset on OSX.
      w->WriteULEB128(current_abbreviation++);  // Abbreviation code.
      w->WriteULEB128(DW_TAG_SUBPROGRAM);
      w->Write<uint8_t>(DW_CHILDREN_YES);
      w->WriteULEB128(DW_AT_NAME);
      w->WriteULEB128(DW_FORM_STRING);
      w->WriteULEB128(DW_AT_LOW_PC);
      w->WriteULEB128(DW_FORM_ADDR);
      w->WriteULEB128(DW_AT_HIGH_PC);
      w->WriteULEB128(DW_FORM_ADDR);
      w->WriteULEB128(DW_AT_FRAME_BASE);
      w->WriteULEB128(DW_FORM_BLOCK4);
      w->WriteULEB128(0);
      w->WriteULEB128(0);

      w->WriteULEB128(current_abbreviation++);
      w->WriteULEB128(DW_TAG_STRUCTURE_TYPE);
      w->Write<uint8_t>(DW_CHILDREN_NO);
      w->WriteULEB128(DW_AT_BYTE_SIZE);
      w->WriteULEB128(DW_FORM_DATA1);
      w->WriteULEB128(DW_AT_NAME);
      w->WriteULEB128(DW_FORM_STRING);
      w->WriteULEB128(0);
      w->WriteULEB128(0);

      for (int param = 0; param < params; ++param) {
        WriteVariableAbbreviation(w, current_abbreviation++, true, true);
      }

      for (int slot = 0; slot < slots; ++slot) {
        WriteVariableAbbreviation(w, current_abbreviation++, false, false);
      }

      for (int internal_slot = 0;
           internal_slot < internal_slots;
           ++internal_slot) {
        WriteVariableAbbreviation(w, current_abbreviation++, false, false);
      }

      for (int context_slot = 0;
           context_slot < context_slots;
           ++context_slot) {
        WriteVariableAbbreviation(w, current_abbreviation++, false, false);
      }

      for (int local = 0; local < locals; ++local) {
        WriteVariableAbbreviation(w, current_abbreviation++, true, false);
      }

      // The function.
      WriteVariableAbbreviation(w, current_abbreviation++, true, false);

      // The context.
      WriteVariableAbbreviation(w, current_abbreviation++, true, false);

      w->WriteULEB128(0);  // Terminate the sibling list.
    }

    w->WriteULEB128(0);  // Terminate the table.
    return true;
  }

 private:
  CodeDescription* desc_;
};


class DebugLineSection : public DebugSection {
 public:
  explicit DebugLineSection(CodeDescription* desc)
#ifdef __ELF
      : ELFSection(".debug_line", TYPE_PROGBITS, 1),
#else
      : MachOSection("__debug_line",
                     "__DWARF",
                     1,
                     MachOSection::S_REGULAR | MachOSection::S_ATTR_DEBUG),
#endif
        desc_(desc) { }

  // DWARF2 standard, figure 34.
  enum DWARF2Opcodes {
    DW_LNS_COPY = 1,
    DW_LNS_ADVANCE_PC = 2,
    DW_LNS_ADVANCE_LINE = 3,
    DW_LNS_SET_FILE = 4,
    DW_LNS_SET_COLUMN = 5,
    DW_LNS_NEGATE_STMT = 6
  };

  // DWARF2 standard, figure 35.
  enum DWARF2ExtendedOpcode {
    DW_LNE_END_SEQUENCE = 1,
    DW_LNE_SET_ADDRESS = 2,
    DW_LNE_DEFINE_FILE = 3
  };

  bool WriteBodyInternal(Writer* w) {
    // Write prologue.
    Writer::Slot<uint32_t> total_length = w->CreateSlotHere<uint32_t>();
    uintptr_t start = w->position();

    // Used for special opcodes
    const int8_t line_base = 1;
    const uint8_t line_range = 7;
    const int8_t max_line_incr = (line_base + line_range - 1);
    const uint8_t opcode_base = DW_LNS_NEGATE_STMT + 1;

    w->Write<uint16_t>(2);  // Field version.
    Writer::Slot<uint32_t> prologue_length = w->CreateSlotHere<uint32_t>();
    uintptr_t prologue_start = w->position();
    w->Write<uint8_t>(1);  // Field minimum_instruction_length.
    w->Write<uint8_t>(1);  // Field default_is_stmt.
    w->Write<int8_t>(line_base);  // Field line_base.
    w->Write<uint8_t>(line_range);  // Field line_range.
    w->Write<uint8_t>(opcode_base);  // Field opcode_base.
    w->Write<uint8_t>(0);  // DW_LNS_COPY operands count.
    w->Write<uint8_t>(1);  // DW_LNS_ADVANCE_PC operands count.
    w->Write<uint8_t>(1);  // DW_LNS_ADVANCE_LINE operands count.
    w->Write<uint8_t>(1);  // DW_LNS_SET_FILE operands count.
    w->Write<uint8_t>(1);  // DW_LNS_SET_COLUMN operands count.
    w->Write<uint8_t>(0);  // DW_LNS_NEGATE_STMT operands count.
    w->Write<uint8_t>(0);  // Empty include_directories sequence.
    w->WriteString(desc_->GetFilename().get());  // File name.
    w->WriteULEB128(0);  // Current directory.
    w->WriteULEB128(0);  // Unknown modification time.
    w->WriteULEB128(0);  // Unknown file size.
    w->Write<uint8_t>(0);
    prologue_length.set(static_cast<uint32_t>(w->position() - prologue_start));

    WriteExtendedOpcode(w, DW_LNE_SET_ADDRESS, sizeof(intptr_t));
    w->Write<intptr_t>(desc_->CodeStart());
    w->Write<uint8_t>(DW_LNS_COPY);

    intptr_t pc = 0;
    intptr_t line = 1;
    bool is_statement = true;

    List<LineInfo::PCInfo>* pc_info = desc_->lineinfo()->pc_info();
    pc_info->Sort(&ComparePCInfo);

    int pc_info_length = pc_info->length();
    for (int i = 0; i < pc_info_length; i++) {
      LineInfo::PCInfo* info = &pc_info->at(i);
      DCHECK(info->pc_ >= pc);

      // Reduce bloating in the debug line table by removing duplicate line
      // entries (per DWARF2 standard).
      intptr_t  new_line = desc_->GetScriptLineNumber(info->pos_);
      if (new_line == line) {
        continue;
      }

      // Mark statement boundaries.  For a better debugging experience, mark
      // the last pc address in the function as a statement (e.g. "}"), so that
      // a user can see the result of the last line executed in the function,
      // should control reach the end.
      if ((i+1) == pc_info_length) {
        if (!is_statement) {
          w->Write<uint8_t>(DW_LNS_NEGATE_STMT);
        }
      } else if (is_statement != info->is_statement_) {
        w->Write<uint8_t>(DW_LNS_NEGATE_STMT);
        is_statement = !is_statement;
      }

      // Generate special opcodes, if possible.  This results in more compact
      // debug line tables.  See the DWARF 2.0 standard to learn more about
      // special opcodes.
      uintptr_t pc_diff = info->pc_ - pc;
      intptr_t line_diff = new_line - line;

      // Compute special opcode (see DWARF 2.0 standard)
      intptr_t special_opcode = (line_diff - line_base) +
                                (line_range * pc_diff) + opcode_base;

      // If special_opcode is less than or equal to 255, it can be used as a
      // special opcode.  If line_diff is larger than the max line increment
      // allowed for a special opcode, or if line_diff is less than the minimum
      // line that can be added to the line register (i.e. line_base), then
      // special_opcode can't be used.
      if ((special_opcode >= opcode_base) && (special_opcode <= 255) &&
          (line_diff <= max_line_incr) && (line_diff >= line_base)) {
        w->Write<uint8_t>(special_opcode);
      } else {
        w->Write<uint8_t>(DW_LNS_ADVANCE_PC);
        w->WriteSLEB128(pc_diff);
        w->Write<uint8_t>(DW_LNS_ADVANCE_LINE);
        w->WriteSLEB128(line_diff);
        w->Write<uint8_t>(DW_LNS_COPY);
      }

      // Increment the pc and line operands.
      pc += pc_diff;
      line += line_diff;
    }
    // Advance the pc to the end of the routine, since the end sequence opcode
    // requires this.
    w->Write<uint8_t>(DW_LNS_ADVANCE_PC);
    w->WriteSLEB128(desc_->CodeSize() - pc);
    WriteExtendedOpcode(w, DW_LNE_END_SEQUENCE, 0);
    total_length.set(static_cast<uint32_t>(w->position() - start));
    return true;
  }

 private:
  void WriteExtendedOpcode(Writer* w,
                           DWARF2ExtendedOpcode op,
                           size_t operands_size) {
    w->Write<uint8_t>(0);
    w->WriteULEB128(operands_size + 1);
    w->Write<uint8_t>(op);
  }

  static int ComparePCInfo(const LineInfo::PCInfo* a,
                           const LineInfo::PCInfo* b) {
    if (a->pc_ == b->pc_) {
      if (a->is_statement_ != b->is_statement_) {
        return b->is_statement_ ? +1 : -1;
      }
      return 0;
    } else if (a->pc_ > b->pc_) {
      return +1;
    } else {
      return -1;
    }
  }

  CodeDescription* desc_;
};


#if V8_TARGET_ARCH_X64

class UnwindInfoSection : public DebugSection {
 public:
  explicit UnwindInfoSection(CodeDescription* desc);
  virtual bool WriteBodyInternal(Writer* w);

  int WriteCIE(Writer* w);
  void WriteFDE(Writer* w, int);

  void WriteFDEStateOnEntry(Writer* w);
  void WriteFDEStateAfterRBPPush(Writer* w);
  void WriteFDEStateAfterRBPSet(Writer* w);
  void WriteFDEStateAfterRBPPop(Writer* w);

  void WriteLength(Writer* w,
                   Writer::Slot<uint32_t>* length_slot,
                   int initial_position);

 private:
  CodeDescription* desc_;

  // DWARF3 Specification, Table 7.23
  enum CFIInstructions {
    DW_CFA_ADVANCE_LOC = 0x40,
    DW_CFA_OFFSET = 0x80,
    DW_CFA_RESTORE = 0xC0,
    DW_CFA_NOP = 0x00,
    DW_CFA_SET_LOC = 0x01,
    DW_CFA_ADVANCE_LOC1 = 0x02,
    DW_CFA_ADVANCE_LOC2 = 0x03,
    DW_CFA_ADVANCE_LOC4 = 0x04,
    DW_CFA_OFFSET_EXTENDED = 0x05,
    DW_CFA_RESTORE_EXTENDED = 0x06,
    DW_CFA_UNDEFINED = 0x07,
    DW_CFA_SAME_VALUE = 0x08,
    DW_CFA_REGISTER = 0x09,
    DW_CFA_REMEMBER_STATE = 0x0A,
    DW_CFA_RESTORE_STATE = 0x0B,
    DW_CFA_DEF_CFA = 0x0C,
    DW_CFA_DEF_CFA_REGISTER = 0x0D,
    DW_CFA_DEF_CFA_OFFSET = 0x0E,

    DW_CFA_DEF_CFA_EXPRESSION = 0x0F,
    DW_CFA_EXPRESSION = 0x10,
    DW_CFA_OFFSET_EXTENDED_SF = 0x11,
    DW_CFA_DEF_CFA_SF = 0x12,
    DW_CFA_DEF_CFA_OFFSET_SF = 0x13,
    DW_CFA_VAL_OFFSET = 0x14,
    DW_CFA_VAL_OFFSET_SF = 0x15,
    DW_CFA_VAL_EXPRESSION = 0x16
  };

  // System V ABI, AMD64 Supplement, Version 0.99.5, Figure 3.36
  enum RegisterMapping {
    // Only the relevant ones have been added to reduce clutter.
    AMD64_RBP = 6,
    AMD64_RSP = 7,
    AMD64_RA = 16
  };

  enum CFIConstants {
    CIE_ID = 0,
    CIE_VERSION = 1,
    CODE_ALIGN_FACTOR = 1,
    DATA_ALIGN_FACTOR = 1,
    RETURN_ADDRESS_REGISTER = AMD64_RA
  };
};


void UnwindInfoSection::WriteLength(Writer* w,
                                    Writer::Slot<uint32_t>* length_slot,
                                    int initial_position) {
  uint32_t align = (w->position() - initial_position) % kPointerSize;

  if (align != 0) {
    for (uint32_t i = 0; i < (kPointerSize - align); i++) {
      w->Write<uint8_t>(DW_CFA_NOP);
    }
  }

  DCHECK((w->position() - initial_position) % kPointerSize == 0);
  length_slot->set(static_cast<uint32_t>(w->position() - initial_position));
}


UnwindInfoSection::UnwindInfoSection(CodeDescription* desc)
#ifdef __ELF
    : ELFSection(".eh_frame", TYPE_X86_64_UNWIND, 1),
#else
    : MachOSection("__eh_frame", "__TEXT", sizeof(uintptr_t),
                   MachOSection::S_REGULAR),
#endif
      desc_(desc) { }

int UnwindInfoSection::WriteCIE(Writer* w) {
  Writer::Slot<uint32_t> cie_length_slot = w->CreateSlotHere<uint32_t>();
  uint32_t cie_position = static_cast<uint32_t>(w->position());

  // Write out the CIE header. Currently no 'common instructions' are
  // emitted onto the CIE; every FDE has its own set of instructions.

  w->Write<uint32_t>(CIE_ID);
  w->Write<uint8_t>(CIE_VERSION);
  w->Write<uint8_t>(0);  // Null augmentation string.
  w->WriteSLEB128(CODE_ALIGN_FACTOR);
  w->WriteSLEB128(DATA_ALIGN_FACTOR);
  w->Write<uint8_t>(RETURN_ADDRESS_REGISTER);

  WriteLength(w, &cie_length_slot, cie_position);

  return cie_position;
}


void UnwindInfoSection::WriteFDE(Writer* w, int cie_position) {
  // The only FDE for this function. The CFA is the current RBP.
  Writer::Slot<uint32_t> fde_length_slot = w->CreateSlotHere<uint32_t>();
  int fde_position = static_cast<uint32_t>(w->position());
  w->Write<int32_t>(fde_position - cie_position + 4);

  w->Write<uintptr_t>(desc_->CodeStart());
  w->Write<uintptr_t>(desc_->CodeSize());

  WriteFDEStateOnEntry(w);
  WriteFDEStateAfterRBPPush(w);
  WriteFDEStateAfterRBPSet(w);
  WriteFDEStateAfterRBPPop(w);

  WriteLength(w, &fde_length_slot, fde_position);
}


void UnwindInfoSection::WriteFDEStateOnEntry(Writer* w) {
  // The first state, just after the control has been transferred to the the
  // function.

  // RBP for this function will be the value of RSP after pushing the RBP
  // for the previous function. The previous RBP has not been pushed yet.
  w->Write<uint8_t>(DW_CFA_DEF_CFA_SF);
  w->WriteULEB128(AMD64_RSP);
  w->WriteSLEB128(-kPointerSize);

  // The RA is stored at location CFA + kCallerPCOffset. This is an invariant,
  // and hence omitted from the next states.
  w->Write<uint8_t>(DW_CFA_OFFSET_EXTENDED);
  w->WriteULEB128(AMD64_RA);
  w->WriteSLEB128(StandardFrameConstants::kCallerPCOffset);

  // The RBP of the previous function is still in RBP.
  w->Write<uint8_t>(DW_CFA_SAME_VALUE);
  w->WriteULEB128(AMD64_RBP);

  // Last location described by this entry.
  w->Write<uint8_t>(DW_CFA_SET_LOC);
  w->Write<uint64_t>(
      desc_->GetStackStateStartAddress(CodeDescription::POST_RBP_PUSH));
}


void UnwindInfoSection::WriteFDEStateAfterRBPPush(Writer* w) {
  // The second state, just after RBP has been pushed.

  // RBP / CFA for this function is now the current RSP, so just set the
  // offset from the previous rule (from -8) to 0.
  w->Write<uint8_t>(DW_CFA_DEF_CFA_OFFSET);
  w->WriteULEB128(0);

  // The previous RBP is stored at CFA + kCallerFPOffset. This is an invariant
  // in this and the next state, and hence omitted in the next state.
  w->Write<uint8_t>(DW_CFA_OFFSET_EXTENDED);
  w->WriteULEB128(AMD64_RBP);
  w->WriteSLEB128(StandardFrameConstants::kCallerFPOffset);

  // Last location described by this entry.
  w->Write<uint8_t>(DW_CFA_SET_LOC);
  w->Write<uint64_t>(
      desc_->GetStackStateStartAddress(CodeDescription::POST_RBP_SET));
}


void UnwindInfoSection::WriteFDEStateAfterRBPSet(Writer* w) {
  // The third state, after the RBP has been set.

  // The CFA can now directly be set to RBP.
  w->Write<uint8_t>(DW_CFA_DEF_CFA);
  w->WriteULEB128(AMD64_RBP);
  w->WriteULEB128(0);

  // Last location described by this entry.
  w->Write<uint8_t>(DW_CFA_SET_LOC);
  w->Write<uint64_t>(
      desc_->GetStackStateStartAddress(CodeDescription::POST_RBP_POP));
}


void UnwindInfoSection::WriteFDEStateAfterRBPPop(Writer* w) {
  // The fourth (final) state. The RBP has been popped (just before issuing a
  // return).

  // The CFA can is now calculated in the same way as in the first state.
  w->Write<uint8_t>(DW_CFA_DEF_CFA_SF);
  w->WriteULEB128(AMD64_RSP);
  w->WriteSLEB128(-kPointerSize);

  // The RBP
  w->Write<uint8_t>(DW_CFA_OFFSET_EXTENDED);
  w->WriteULEB128(AMD64_RBP);
  w->WriteSLEB128(StandardFrameConstants::kCallerFPOffset);

  // Last location described by this entry.
  w->Write<uint8_t>(DW_CFA_SET_LOC);
  w->Write<uint64_t>(desc_->CodeEnd());
}


bool UnwindInfoSection::WriteBodyInternal(Writer* w) {
  uint32_t cie_position = WriteCIE(w);
  WriteFDE(w, cie_position);
  return true;
}


#endif  // V8_TARGET_ARCH_X64

static void CreateDWARFSections(CodeDescription* desc,
                                Zone* zone,
                                DebugObject* obj) {
  if (desc->IsLineInfoAvailable()) {
    obj->AddSection(new(zone) DebugInfoSection(desc));
    obj->AddSection(new(zone) DebugAbbrevSection(desc));
    obj->AddSection(new(zone) DebugLineSection(desc));
  }
#if V8_TARGET_ARCH_X64
  obj->AddSection(new(zone) UnwindInfoSection(desc));
#endif
}


// -------------------------------------------------------------------
// Binary GDB JIT Interface as described in
//   http://sourceware.org/gdb/onlinedocs/gdb/Declarations.html
extern "C" {
  typedef enum {
    JIT_NOACTION = 0,
    JIT_REGISTER_FN,
    JIT_UNREGISTER_FN
  } JITAction;

  struct JITCodeEntry {
    JITCodeEntry* next_;
    JITCodeEntry* prev_;
    Address symfile_addr_;
    uint64_t symfile_size_;
  };

  struct JITDescriptor {
    uint32_t version_;
    uint32_t action_flag_;
    JITCodeEntry* relevant_entry_;
    JITCodeEntry* first_entry_;
  };

  // GDB will place breakpoint into this function.
  // To prevent GCC from inlining or removing it we place noinline attribute
  // and inline assembler statement inside.
  void __attribute__((noinline)) __jit_debug_register_code() {
    __asm__("");
  }

  // GDB will inspect contents of this descriptor.
  // Static initialization is necessary to prevent GDB from seeing
  // uninitialized descriptor.
  JITDescriptor __jit_debug_descriptor = { 1, 0, 0, 0 };

#ifdef OBJECT_PRINT
  void __gdb_print_v8_object(Object* object) {
    OFStream os(stdout);
    object->Print(os);
    os << std::flush;
  }
#endif
}


static JITCodeEntry* CreateCodeEntry(Address symfile_addr,
                                     uintptr_t symfile_size) {
  JITCodeEntry* entry = static_cast<JITCodeEntry*>(
      malloc(sizeof(JITCodeEntry) + symfile_size));

  entry->symfile_addr_ = reinterpret_cast<Address>(entry + 1);
  entry->symfile_size_ = symfile_size;
  MemCopy(entry->symfile_addr_, symfile_addr, symfile_size);

  entry->prev_ = entry->next_ = NULL;

  return entry;
}


static void DestroyCodeEntry(JITCodeEntry* entry) {
  free(entry);
}


static void RegisterCodeEntry(JITCodeEntry* entry) {
  entry->next_ = __jit_debug_descriptor.first_entry_;
  if (entry->next_ != NULL) entry->next_->prev_ = entry;
  __jit_debug_descriptor.first_entry_ =
      __jit_debug_descriptor.relevant_entry_ = entry;

  __jit_debug_descriptor.action_flag_ = JIT_REGISTER_FN;
  __jit_debug_register_code();
}


static void UnregisterCodeEntry(JITCodeEntry* entry) {
  if (entry->prev_ != NULL) {
    entry->prev_->next_ = entry->next_;
  } else {
    __jit_debug_descriptor.first_entry_ = entry->next_;
  }

  if (entry->next_ != NULL) {
    entry->next_->prev_ = entry->prev_;
  }

  __jit_debug_descriptor.relevant_entry_ = entry;
  __jit_debug_descriptor.action_flag_ = JIT_UNREGISTER_FN;
  __jit_debug_register_code();
}


static JITCodeEntry* CreateELFObject(CodeDescription* desc, Isolate* isolate) {
#ifdef __MACH_O
  Zone zone;
  MachO mach_o(&zone);
  Writer w(&mach_o);

  mach_o.AddSection(new(&zone) MachOTextSection(kCodeAlignment,
                                                desc->CodeStart(),
                                                desc->CodeSize()));

  CreateDWARFSections(desc, &zone, &mach_o);

  mach_o.Write(&w, desc->CodeStart(), desc->CodeSize());
#else
  Zone zone;
  ELF elf(&zone);
  Writer w(&elf);

  int text_section_index = elf.AddSection(
      new(&zone) FullHeaderELFSection(
          ".text",
          ELFSection::TYPE_NOBITS,
          kCodeAlignment,
          desc->CodeStart(),
          0,
          desc->CodeSize(),
          ELFSection::FLAG_ALLOC | ELFSection::FLAG_EXEC));

  CreateSymbolsTable(desc, &zone, &elf, text_section_index);

  CreateDWARFSections(desc, &zone, &elf);

  elf.Write(&w);
#endif

  return CreateCodeEntry(w.buffer(), w.position());
}


struct AddressRange {
  Address start;
  Address end;
};

struct SplayTreeConfig {
  typedef AddressRange Key;
  typedef JITCodeEntry* Value;
  static const AddressRange kNoKey;
  static Value NoValue() { return NULL; }
  static int Compare(const AddressRange& a, const AddressRange& b) {
    // ptrdiff_t probably doesn't fit in an int.
    if (a.start < b.start) return -1;
    if (a.start == b.start) return 0;
    return 1;
  }
};

const AddressRange SplayTreeConfig::kNoKey = {0, 0};
typedef SplayTree<SplayTreeConfig> CodeMap;

static CodeMap* GetCodeMap() {
  static CodeMap* code_map = NULL;
  if (code_map == NULL) code_map = new CodeMap();
  return code_map;
}


static uint32_t HashCodeAddress(Address addr) {
  static const uintptr_t kGoldenRatio = 2654435761u;
  uintptr_t offset = OffsetFrom(addr);
  return static_cast<uint32_t>((offset >> kCodeAlignmentBits) * kGoldenRatio);
}


static HashMap* GetLineMap() {
  static HashMap* line_map = NULL;
  if (line_map == NULL) line_map = new HashMap(&HashMap::PointersMatch);
  return line_map;
}


static void PutLineInfo(Address addr, LineInfo* info) {
  HashMap* line_map = GetLineMap();
  HashMap::Entry* e = line_map->LookupOrInsert(addr, HashCodeAddress(addr));
  if (e->value != NULL) delete static_cast<LineInfo*>(e->value);
  e->value = info;
}


static LineInfo* GetLineInfo(Address addr) {
  void* value = GetLineMap()->Remove(addr, HashCodeAddress(addr));
  return static_cast<LineInfo*>(value);
}


static void AddUnwindInfo(CodeDescription* desc) {
#if V8_TARGET_ARCH_X64
  if (desc->is_function()) {
    // To avoid propagating unwinding information through
    // compilation pipeline we use an approximation.
    // For most use cases this should not affect usability.
    static const int kFramePointerPushOffset = 1;
    static const int kFramePointerSetOffset = 4;
    static const int kFramePointerPopOffset = -3;

    uintptr_t frame_pointer_push_address =
        desc->CodeStart() + kFramePointerPushOffset;

    uintptr_t frame_pointer_set_address =
        desc->CodeStart() + kFramePointerSetOffset;

    uintptr_t frame_pointer_pop_address =
        desc->CodeEnd() + kFramePointerPopOffset;

    desc->SetStackStateStartAddress(CodeDescription::POST_RBP_PUSH,
                                    frame_pointer_push_address);
    desc->SetStackStateStartAddress(CodeDescription::POST_RBP_SET,
                                    frame_pointer_set_address);
    desc->SetStackStateStartAddress(CodeDescription::POST_RBP_POP,
                                    frame_pointer_pop_address);
  } else {
    desc->SetStackStateStartAddress(CodeDescription::POST_RBP_PUSH,
                                    desc->CodeStart());
    desc->SetStackStateStartAddress(CodeDescription::POST_RBP_SET,
                                    desc->CodeStart());
    desc->SetStackStateStartAddress(CodeDescription::POST_RBP_POP,
                                    desc->CodeEnd());
  }
#endif  // V8_TARGET_ARCH_X64
}


static base::LazyMutex mutex = LAZY_MUTEX_INITIALIZER;


// Remove entries from the splay tree that intersect the given address range,
// and deregister them from GDB.
static void RemoveJITCodeEntries(CodeMap* map, const AddressRange& range) {
  DCHECK(range.start < range.end);
  CodeMap::Locator cur;
  if (map->FindGreatestLessThan(range, &cur) || map->FindLeast(&cur)) {
    // Skip entries that are entirely less than the range of interest.
    while (cur.key().end <= range.start) {
      // CodeMap::FindLeastGreaterThan succeeds for entries whose key is greater
      // than _or equal to_ the given key, so we have to advance our key to get
      // the next one.
      AddressRange new_key;
      new_key.start = cur.key().end;
      new_key.end = 0;
      if (!map->FindLeastGreaterThan(new_key, &cur)) return;
    }
    // Evict intersecting ranges.
    while (cur.key().start < range.end) {
      AddressRange old_range = cur.key();
      JITCodeEntry* old_entry = cur.value();

      UnregisterCodeEntry(old_entry);
      DestroyCodeEntry(old_entry);

      CHECK(map->Remove(old_range));
      if (!map->FindLeastGreaterThan(old_range, &cur)) return;
    }
  }
}


// Insert the entry into the splay tree and register it with GDB.
static void AddJITCodeEntry(CodeMap* map, const AddressRange& range,
                            JITCodeEntry* entry, bool dump_if_enabled,
                            const char* name_hint) {
#if defined(DEBUG) && !V8_OS_WIN
  static int file_num = 0;
  if (FLAG_gdbjit_dump && dump_if_enabled) {
    static const int kMaxFileNameSize = 64;
    char file_name[64];

    SNPrintF(Vector<char>(file_name, kMaxFileNameSize), "/tmp/elfdump%s%d.o",
             (name_hint != NULL) ? name_hint : "", file_num++);
    WriteBytes(file_name, entry->symfile_addr_,
               static_cast<int>(entry->symfile_size_));
  }
#endif

  CodeMap::Locator cur;
  CHECK(map->Insert(range, &cur));
  cur.set_value(entry);

  RegisterCodeEntry(entry);
}


static void AddCode(const char* name, Code* code, SharedFunctionInfo* shared,
                    LineInfo* lineinfo) {
  DisallowHeapAllocation no_gc;

  CodeMap* code_map = GetCodeMap();
  AddressRange range;
  range.start = code->address();
  range.end = code->address() + code->CodeSize();
  RemoveJITCodeEntries(code_map, range);

  CodeDescription code_desc(name, code, shared, lineinfo);

  if (!FLAG_gdbjit_full && !code_desc.IsLineInfoAvailable()) {
    delete lineinfo;
    return;
  }

  AddUnwindInfo(&code_desc);
  Isolate* isolate = code->GetIsolate();
  JITCodeEntry* entry = CreateELFObject(&code_desc, isolate);

  delete lineinfo;

  const char* name_hint = NULL;
  bool should_dump = false;
  if (FLAG_gdbjit_dump) {
    if (strlen(FLAG_gdbjit_dump_filter) == 0) {
      name_hint = name;
      should_dump = true;
    } else if (name != NULL) {
      name_hint = strstr(name, FLAG_gdbjit_dump_filter);
      should_dump = (name_hint != NULL);
    }
  }
  AddJITCodeEntry(code_map, range, entry, should_dump, name_hint);
}


void EventHandler(const v8::JitCodeEvent* event) {
  if (!FLAG_gdbjit) return;
  base::LockGuard<base::Mutex> lock_guard(mutex.Pointer());
  switch (event->type) {
    case v8::JitCodeEvent::CODE_ADDED: {
      Address addr = reinterpret_cast<Address>(event->code_start);
      Code* code = Code::GetCodeFromTargetAddress(addr);
      LineInfo* lineinfo = GetLineInfo(addr);
      EmbeddedVector<char, 256> buffer;
      StringBuilder builder(buffer.start(), buffer.length());
      builder.AddSubstring(event->name.str, static_cast<int>(event->name.len));
      // It's called UnboundScript in the API but it's a SharedFunctionInfo.
      SharedFunctionInfo* shared =
          event->script.IsEmpty() ? NULL : *Utils::OpenHandle(*event->script);
      AddCode(builder.Finalize(), code, shared, lineinfo);
      break;
    }
    case v8::JitCodeEvent::CODE_MOVED:
      // Enabling the GDB JIT interface should disable code compaction.
      UNREACHABLE();
      break;
    case v8::JitCodeEvent::CODE_REMOVED:
      // Do nothing.  Instead, adding code causes eviction of any entry whose
      // address range intersects the address range of the added code.
      break;
    case v8::JitCodeEvent::CODE_ADD_LINE_POS_INFO: {
      LineInfo* line_info = reinterpret_cast<LineInfo*>(event->user_data);
      line_info->SetPosition(static_cast<intptr_t>(event->line_info.offset),
                             static_cast<int>(event->line_info.pos),
                             event->line_info.position_type ==
                                 v8::JitCodeEvent::STATEMENT_POSITION);
      break;
    }
    case v8::JitCodeEvent::CODE_START_LINE_INFO_RECORDING: {
      v8::JitCodeEvent* mutable_event = const_cast<v8::JitCodeEvent*>(event);
      mutable_event->user_data = new LineInfo();
      break;
    }
    case v8::JitCodeEvent::CODE_END_LINE_INFO_RECORDING: {
      LineInfo* line_info = reinterpret_cast<LineInfo*>(event->user_data);
      PutLineInfo(reinterpret_cast<Address>(event->code_start), line_info);
      break;
    }
  }
}
#endif
}  // namespace GDBJITInterface
}  // namespace internal
}  // namespace v8