aboutsummaryrefslogtreecommitdiffstats
path: root/ELF/SyntheticSections.cpp
blob: f6d0f190d84d07711ae2aae83b592c236092aa5e (plain) (blame)
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
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
3280
3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
3321
3322
3323
3324
3325
3326
3327
3328
3329
3330
3331
3332
3333
3334
3335
3336
3337
3338
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
3368
3369
3370
3371
3372
3373
3374
3375
3376
3377
3378
3379
3380
3381
3382
3383
3384
3385
3386
3387
3388
3389
3390
3391
3392
3393
3394
3395
3396
3397
3398
3399
3400
3401
3402
3403
3404
3405
3406
3407
3408
3409
3410
3411
3412
3413
3414
3415
3416
3417
3418
3419
3420
3421
3422
3423
3424
3425
3426
3427
3428
3429
3430
3431
3432
3433
3434
3435
3436
3437
3438
3439
3440
3441
3442
3443
3444
3445
3446
3447
3448
3449
3450
3451
3452
3453
3454
3455
3456
3457
3458
3459
3460
3461
3462
3463
3464
3465
3466
3467
3468
3469
3470
3471
3472
3473
3474
3475
3476
3477
3478
3479
3480
3481
3482
3483
3484
3485
3486
3487
3488
3489
3490
3491
3492
3493
3494
3495
3496
3497
3498
3499
3500
3501
3502
3503
3504
3505
3506
3507
3508
3509
3510
3511
3512
3513
3514
3515
3516
3517
3518
3519
3520
3521
3522
3523
3524
3525
3526
3527
3528
3529
3530
3531
3532
3533
3534
3535
3536
3537
3538
3539
3540
3541
3542
3543
3544
3545
3546
3547
3548
3549
3550
3551
3552
3553
3554
3555
3556
3557
3558
3559
3560
3561
3562
3563
3564
3565
3566
3567
3568
3569
3570
3571
3572
3573
3574
3575
3576
3577
3578
3579
3580
3581
3582
3583
3584
3585
3586
3587
3588
3589
3590
3591
3592
3593
3594
3595
3596
3597
3598
3599
3600
3601
3602
3603
3604
3605
3606
3607
3608
3609
3610
3611
3612
3613
3614
3615
3616
3617
3618
//===- SyntheticSections.cpp ----------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file contains linker-synthesized sections. Currently,
// synthetic sections are created either output sections or input sections,
// but we are rewriting code so that all synthetic sections are created as
// input sections.
//
//===----------------------------------------------------------------------===//

#include "SyntheticSections.h"
#include "Config.h"
#include "InputFiles.h"
#include "LinkerScript.h"
#include "OutputSections.h"
#include "SymbolTable.h"
#include "Symbols.h"
#include "Target.h"
#include "Writer.h"
#include "lld/Common/ErrorHandler.h"
#include "lld/Common/Memory.h"
#include "lld/Common/Strings.h"
#include "lld/Common/Threads.h"
#include "lld/Common/Version.h"
#include "llvm/ADT/SetOperations.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/BinaryFormat/Dwarf.h"
#include "llvm/DebugInfo/DWARF/DWARFDebugPubTable.h"
#include "llvm/Object/ELFObjectFile.h"
#include "llvm/Support/Compression.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/LEB128.h"
#include "llvm/Support/MD5.h"
#include <cstdlib>
#include <thread>

using namespace llvm;
using namespace llvm::dwarf;
using namespace llvm::ELF;
using namespace llvm::object;
using namespace llvm::support;

using namespace lld;
using namespace lld::elf;

using llvm::support::endian::read32le;
using llvm::support::endian::write32le;
using llvm::support::endian::write64le;

constexpr size_t MergeNoTailSection::numShards;

static uint64_t readUint(uint8_t *buf) {
  return config->is64 ? read64(buf) : read32(buf);
}

static void writeUint(uint8_t *buf, uint64_t val) {
  if (config->is64)
    write64(buf, val);
  else
    write32(buf, val);
}

// Returns an LLD version string.
static ArrayRef<uint8_t> getVersion() {
  // Check LLD_VERSION first for ease of testing.
  // You can get consistent output by using the environment variable.
  // This is only for testing.
  StringRef s = getenv("LLD_VERSION");
  if (s.empty())
    s = saver.save(Twine("Linker: ") + getLLDVersion());

  // +1 to include the terminating '\0'.
  return {(const uint8_t *)s.data(), s.size() + 1};
}

// Creates a .comment section containing LLD version info.
// With this feature, you can identify LLD-generated binaries easily
// by "readelf --string-dump .comment <file>".
// The returned object is a mergeable string section.
MergeInputSection *elf::createCommentSection() {
  return make<MergeInputSection>(SHF_MERGE | SHF_STRINGS, SHT_PROGBITS, 1,
                                 getVersion(), ".comment");
}

// .MIPS.abiflags section.
template <class ELFT>
MipsAbiFlagsSection<ELFT>::MipsAbiFlagsSection(Elf_Mips_ABIFlags flags)
    : SyntheticSection(SHF_ALLOC, SHT_MIPS_ABIFLAGS, 8, ".MIPS.abiflags"),
      flags(flags) {
  this->entsize = sizeof(Elf_Mips_ABIFlags);
}

template <class ELFT> void MipsAbiFlagsSection<ELFT>::writeTo(uint8_t *buf) {
  memcpy(buf, &flags, sizeof(flags));
}

template <class ELFT>
MipsAbiFlagsSection<ELFT> *MipsAbiFlagsSection<ELFT>::create() {
  Elf_Mips_ABIFlags flags = {};
  bool create = false;

  for (InputSectionBase *sec : inputSections) {
    if (sec->type != SHT_MIPS_ABIFLAGS)
      continue;
    sec->markDead();
    create = true;

    std::string filename = toString(sec->file);
    const size_t size = sec->data().size();
    // Older version of BFD (such as the default FreeBSD linker) concatenate
    // .MIPS.abiflags instead of merging. To allow for this case (or potential
    // zero padding) we ignore everything after the first Elf_Mips_ABIFlags
    if (size < sizeof(Elf_Mips_ABIFlags)) {
      error(filename + ": invalid size of .MIPS.abiflags section: got " +
            Twine(size) + " instead of " + Twine(sizeof(Elf_Mips_ABIFlags)));
      return nullptr;
    }
    auto *s = reinterpret_cast<const Elf_Mips_ABIFlags *>(sec->data().data());
    if (s->version != 0) {
      error(filename + ": unexpected .MIPS.abiflags version " +
            Twine(s->version));
      return nullptr;
    }

    // LLD checks ISA compatibility in calcMipsEFlags(). Here we just
    // select the highest number of ISA/Rev/Ext.
    flags.isa_level = std::max(flags.isa_level, s->isa_level);
    flags.isa_rev = std::max(flags.isa_rev, s->isa_rev);
    flags.isa_ext = std::max(flags.isa_ext, s->isa_ext);
    flags.gpr_size = std::max(flags.gpr_size, s->gpr_size);
    flags.cpr1_size = std::max(flags.cpr1_size, s->cpr1_size);
    flags.cpr2_size = std::max(flags.cpr2_size, s->cpr2_size);
    flags.ases |= s->ases;
    flags.flags1 |= s->flags1;
    flags.flags2 |= s->flags2;
    flags.fp_abi = elf::getMipsFpAbiFlag(flags.fp_abi, s->fp_abi, filename);
  };

  if (create)
    return make<MipsAbiFlagsSection<ELFT>>(flags);
  return nullptr;
}

// .MIPS.options section.
template <class ELFT>
MipsOptionsSection<ELFT>::MipsOptionsSection(Elf_Mips_RegInfo reginfo)
    : SyntheticSection(SHF_ALLOC, SHT_MIPS_OPTIONS, 8, ".MIPS.options"),
      reginfo(reginfo) {
  this->entsize = sizeof(Elf_Mips_Options) + sizeof(Elf_Mips_RegInfo);
}

template <class ELFT> void MipsOptionsSection<ELFT>::writeTo(uint8_t *buf) {
  auto *options = reinterpret_cast<Elf_Mips_Options *>(buf);
  options->kind = ODK_REGINFO;
  options->size = getSize();

  if (!config->relocatable)
    reginfo.ri_gp_value = in.mipsGot->getGp();
  memcpy(buf + sizeof(Elf_Mips_Options), &reginfo, sizeof(reginfo));
}

template <class ELFT>
MipsOptionsSection<ELFT> *MipsOptionsSection<ELFT>::create() {
  // N64 ABI only.
  if (!ELFT::Is64Bits)
    return nullptr;

  std::vector<InputSectionBase *> sections;
  for (InputSectionBase *sec : inputSections)
    if (sec->type == SHT_MIPS_OPTIONS)
      sections.push_back(sec);

  if (sections.empty())
    return nullptr;

  Elf_Mips_RegInfo reginfo = {};
  for (InputSectionBase *sec : sections) {
    sec->markDead();

    std::string filename = toString(sec->file);
    ArrayRef<uint8_t> d = sec->data();

    while (!d.empty()) {
      if (d.size() < sizeof(Elf_Mips_Options)) {
        error(filename + ": invalid size of .MIPS.options section");
        break;
      }

      auto *opt = reinterpret_cast<const Elf_Mips_Options *>(d.data());
      if (opt->kind == ODK_REGINFO) {
        reginfo.ri_gprmask |= opt->getRegInfo().ri_gprmask;
        sec->getFile<ELFT>()->mipsGp0 = opt->getRegInfo().ri_gp_value;
        break;
      }

      if (!opt->size)
        fatal(filename + ": zero option descriptor size");
      d = d.slice(opt->size);
    }
  };

  return make<MipsOptionsSection<ELFT>>(reginfo);
}

// MIPS .reginfo section.
template <class ELFT>
MipsReginfoSection<ELFT>::MipsReginfoSection(Elf_Mips_RegInfo reginfo)
    : SyntheticSection(SHF_ALLOC, SHT_MIPS_REGINFO, 4, ".reginfo"),
      reginfo(reginfo) {
  this->entsize = sizeof(Elf_Mips_RegInfo);
}

template <class ELFT> void MipsReginfoSection<ELFT>::writeTo(uint8_t *buf) {
  if (!config->relocatable)
    reginfo.ri_gp_value = in.mipsGot->getGp();
  memcpy(buf, &reginfo, sizeof(reginfo));
}

template <class ELFT>
MipsReginfoSection<ELFT> *MipsReginfoSection<ELFT>::create() {
  // Section should be alive for O32 and N32 ABIs only.
  if (ELFT::Is64Bits)
    return nullptr;

  std::vector<InputSectionBase *> sections;
  for (InputSectionBase *sec : inputSections)
    if (sec->type == SHT_MIPS_REGINFO)
      sections.push_back(sec);

  if (sections.empty())
    return nullptr;

  Elf_Mips_RegInfo reginfo = {};
  for (InputSectionBase *sec : sections) {
    sec->markDead();

    if (sec->data().size() != sizeof(Elf_Mips_RegInfo)) {
      error(toString(sec->file) + ": invalid size of .reginfo section");
      return nullptr;
    }

    auto *r = reinterpret_cast<const Elf_Mips_RegInfo *>(sec->data().data());
    reginfo.ri_gprmask |= r->ri_gprmask;
    sec->getFile<ELFT>()->mipsGp0 = r->ri_gp_value;
  };

  return make<MipsReginfoSection<ELFT>>(reginfo);
}

InputSection *elf::createInterpSection() {
  // StringSaver guarantees that the returned string ends with '\0'.
  StringRef s = saver.save(config->dynamicLinker);
  ArrayRef<uint8_t> contents = {(const uint8_t *)s.data(), s.size() + 1};

  auto *sec = make<InputSection>(nullptr, SHF_ALLOC, SHT_PROGBITS, 1, contents,
                                 ".interp");
  sec->markLive();
  return sec;
}

Defined *elf::addSyntheticLocal(StringRef name, uint8_t type, uint64_t value,
                                uint64_t size, InputSectionBase &section) {
  auto *s = make<Defined>(section.file, name, STB_LOCAL, STV_DEFAULT, type,
                          value, size, &section);
  if (in.symTab)
    in.symTab->addSymbol(s);
  return s;
}

static size_t getHashSize() {
  switch (config->buildId) {
  case BuildIdKind::Fast:
    return 8;
  case BuildIdKind::Md5:
  case BuildIdKind::Uuid:
    return 16;
  case BuildIdKind::Sha1:
    return 20;
  case BuildIdKind::Hexstring:
    return config->buildIdVector.size();
  default:
    llvm_unreachable("unknown BuildIdKind");
  }
}

// This class represents a linker-synthesized .note.gnu.property section.
//
// In x86 and AArch64, object files may contain feature flags indicating the
// features that they have used. The flags are stored in a .note.gnu.property
// section.
//
// lld reads the sections from input files and merges them by computing AND of
// the flags. The result is written as a new .note.gnu.property section.
//
// If the flag is zero (which indicates that the intersection of the feature
// sets is empty, or some input files didn't have .note.gnu.property sections),
// we don't create this section.
GnuPropertySection::GnuPropertySection()
    : SyntheticSection(llvm::ELF::SHF_ALLOC, llvm::ELF::SHT_NOTE, 4,
                       ".note.gnu.property") {}

void GnuPropertySection::writeTo(uint8_t *buf) {
  uint32_t featureAndType = config->emachine == EM_AARCH64
                                ? GNU_PROPERTY_AARCH64_FEATURE_1_AND
                                : GNU_PROPERTY_X86_FEATURE_1_AND;

  write32(buf, 4);                                   // Name size
  write32(buf + 4, config->is64 ? 16 : 12);          // Content size
  write32(buf + 8, NT_GNU_PROPERTY_TYPE_0);          // Type
  memcpy(buf + 12, "GNU", 4);                        // Name string
  write32(buf + 16, featureAndType);                 // Feature type
  write32(buf + 20, 4);                              // Feature size
  write32(buf + 24, config->andFeatures);            // Feature flags
  if (config->is64)
    write32(buf + 28, 0); // Padding
}

size_t GnuPropertySection::getSize() const { return config->is64 ? 32 : 28; }

BuildIdSection::BuildIdSection()
    : SyntheticSection(SHF_ALLOC, SHT_NOTE, 4, ".note.gnu.build-id"),
      hashSize(getHashSize()) {}

void BuildIdSection::writeTo(uint8_t *buf) {
  write32(buf, 4);                      // Name size
  write32(buf + 4, hashSize);           // Content size
  write32(buf + 8, NT_GNU_BUILD_ID);    // Type
  memcpy(buf + 12, "GNU", 4);           // Name string
  hashBuf = buf + 16;
}

void BuildIdSection::writeBuildId(ArrayRef<uint8_t> buf) {
  assert(buf.size() == hashSize);
  memcpy(hashBuf, buf.data(), hashSize);
}

BssSection::BssSection(StringRef name, uint64_t size, uint32_t alignment)
    : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_NOBITS, alignment, name) {
  this->bss = true;
  this->size = size;
}

EhFrameSection::EhFrameSection()
    : SyntheticSection(SHF_ALLOC, SHT_PROGBITS, 1, ".eh_frame") {}

// Search for an existing CIE record or create a new one.
// CIE records from input object files are uniquified by their contents
// and where their relocations point to.
template <class ELFT, class RelTy>
CieRecord *EhFrameSection::addCie(EhSectionPiece &cie, ArrayRef<RelTy> rels) {
  Symbol *personality = nullptr;
  unsigned firstRelI = cie.firstRelocation;
  if (firstRelI != (unsigned)-1)
    personality =
        &cie.sec->template getFile<ELFT>()->getRelocTargetSym(rels[firstRelI]);

  // Search for an existing CIE by CIE contents/relocation target pair.
  CieRecord *&rec = cieMap[{cie.data(), personality}];

  // If not found, create a new one.
  if (!rec) {
    rec = make<CieRecord>();
    rec->cie = &cie;
    cieRecords.push_back(rec);
  }
  return rec;
}

// There is one FDE per function. Returns true if a given FDE
// points to a live function.
template <class ELFT, class RelTy>
bool EhFrameSection::isFdeLive(EhSectionPiece &fde, ArrayRef<RelTy> rels) {
  auto *sec = cast<EhInputSection>(fde.sec);
  unsigned firstRelI = fde.firstRelocation;

  // An FDE should point to some function because FDEs are to describe
  // functions. That's however not always the case due to an issue of
  // ld.gold with -r. ld.gold may discard only functions and leave their
  // corresponding FDEs, which results in creating bad .eh_frame sections.
  // To deal with that, we ignore such FDEs.
  if (firstRelI == (unsigned)-1)
    return false;

  const RelTy &rel = rels[firstRelI];
  Symbol &b = sec->template getFile<ELFT>()->getRelocTargetSym(rel);

  // FDEs for garbage-collected or merged-by-ICF sections, or sections in
  // another partition, are dead.
  if (auto *d = dyn_cast<Defined>(&b))
    if (SectionBase *sec = d->section)
      return sec->partition == partition;
  return false;
}

// .eh_frame is a sequence of CIE or FDE records. In general, there
// is one CIE record per input object file which is followed by
// a list of FDEs. This function searches an existing CIE or create a new
// one and associates FDEs to the CIE.
template <class ELFT, class RelTy>
void EhFrameSection::addSectionAux(EhInputSection *sec, ArrayRef<RelTy> rels) {
  offsetToCie.clear();
  for (EhSectionPiece &piece : sec->pieces) {
    // The empty record is the end marker.
    if (piece.size == 4)
      return;

    size_t offset = piece.inputOff;
    uint32_t id = read32(piece.data().data() + 4);
    if (id == 0) {
      offsetToCie[offset] = addCie<ELFT>(piece, rels);
      continue;
    }

    uint32_t cieOffset = offset + 4 - id;
    CieRecord *rec = offsetToCie[cieOffset];
    if (!rec)
      fatal(toString(sec) + ": invalid CIE reference");

    if (!isFdeLive<ELFT>(piece, rels))
      continue;
    rec->fdes.push_back(&piece);
    numFdes++;
  }
}

template <class ELFT> void EhFrameSection::addSection(InputSectionBase *c) {
  auto *sec = cast<EhInputSection>(c);
  sec->parent = this;

  alignment = std::max(alignment, sec->alignment);
  sections.push_back(sec);

  for (auto *ds : sec->dependentSections)
    dependentSections.push_back(ds);

  if (sec->pieces.empty())
    return;

  if (sec->areRelocsRela)
    addSectionAux<ELFT>(sec, sec->template relas<ELFT>());
  else
    addSectionAux<ELFT>(sec, sec->template rels<ELFT>());
}

static void writeCieFde(uint8_t *buf, ArrayRef<uint8_t> d) {
  memcpy(buf, d.data(), d.size());

  size_t aligned = alignTo(d.size(), config->wordsize);

  // Zero-clear trailing padding if it exists.
  memset(buf + d.size(), 0, aligned - d.size());

  // Fix the size field. -4 since size does not include the size field itself.
  write32(buf, aligned - 4);
}

void EhFrameSection::finalizeContents() {
  assert(!this->size); // Not finalized.
  size_t off = 0;
  for (CieRecord *rec : cieRecords) {
    rec->cie->outputOff = off;
    off += alignTo(rec->cie->size, config->wordsize);

    for (EhSectionPiece *fde : rec->fdes) {
      fde->outputOff = off;
      off += alignTo(fde->size, config->wordsize);
    }
  }

  // The LSB standard does not allow a .eh_frame section with zero
  // Call Frame Information records. glibc unwind-dw2-fde.c
  // classify_object_over_fdes expects there is a CIE record length 0 as a
  // terminator. Thus we add one unconditionally.
  off += 4;

  this->size = off;
}

// Returns data for .eh_frame_hdr. .eh_frame_hdr is a binary search table
// to get an FDE from an address to which FDE is applied. This function
// returns a list of such pairs.
std::vector<EhFrameSection::FdeData> EhFrameSection::getFdeData() const {
  uint8_t *buf = Out::bufferStart + getParent()->offset + outSecOff;
  std::vector<FdeData> ret;

  uint64_t va = getPartition().ehFrameHdr->getVA();
  for (CieRecord *rec : cieRecords) {
    uint8_t enc = getFdeEncoding(rec->cie);
    for (EhSectionPiece *fde : rec->fdes) {
      uint64_t pc = getFdePc(buf, fde->outputOff, enc);
      uint64_t fdeVA = getParent()->addr + fde->outputOff;
      if (!isInt<32>(pc - va))
        fatal(toString(fde->sec) + ": PC offset is too large: 0x" +
              Twine::utohexstr(pc - va));
      ret.push_back({uint32_t(pc - va), uint32_t(fdeVA - va)});
    }
  }

  // Sort the FDE list by their PC and uniqueify. Usually there is only
  // one FDE for a PC (i.e. function), but if ICF merges two functions
  // into one, there can be more than one FDEs pointing to the address.
  auto less = [](const FdeData &a, const FdeData &b) {
    return a.pcRel < b.pcRel;
  };
  llvm::stable_sort(ret, less);
  auto eq = [](const FdeData &a, const FdeData &b) {
    return a.pcRel == b.pcRel;
  };
  ret.erase(std::unique(ret.begin(), ret.end(), eq), ret.end());

  return ret;
}

static uint64_t readFdeAddr(uint8_t *buf, int size) {
  switch (size) {
  case DW_EH_PE_udata2:
    return read16(buf);
  case DW_EH_PE_sdata2:
    return (int16_t)read16(buf);
  case DW_EH_PE_udata4:
    return read32(buf);
  case DW_EH_PE_sdata4:
    return (int32_t)read32(buf);
  case DW_EH_PE_udata8:
  case DW_EH_PE_sdata8:
    return read64(buf);
  case DW_EH_PE_absptr:
    return readUint(buf);
  }
  fatal("unknown FDE size encoding");
}

// Returns the VA to which a given FDE (on a mmap'ed buffer) is applied to.
// We need it to create .eh_frame_hdr section.
uint64_t EhFrameSection::getFdePc(uint8_t *buf, size_t fdeOff,
                                  uint8_t enc) const {
  // The starting address to which this FDE applies is
  // stored at FDE + 8 byte.
  size_t off = fdeOff + 8;
  uint64_t addr = readFdeAddr(buf + off, enc & 0xf);
  if ((enc & 0x70) == DW_EH_PE_absptr)
    return addr;
  if ((enc & 0x70) == DW_EH_PE_pcrel)
    return addr + getParent()->addr + off;
  fatal("unknown FDE size relative encoding");
}

void EhFrameSection::writeTo(uint8_t *buf) {
  // Write CIE and FDE records.
  for (CieRecord *rec : cieRecords) {
    size_t cieOffset = rec->cie->outputOff;
    writeCieFde(buf + cieOffset, rec->cie->data());

    for (EhSectionPiece *fde : rec->fdes) {
      size_t off = fde->outputOff;
      writeCieFde(buf + off, fde->data());

      // FDE's second word should have the offset to an associated CIE.
      // Write it.
      write32(buf + off + 4, off + 4 - cieOffset);
    }
  }

  // Apply relocations. .eh_frame section contents are not contiguous
  // in the output buffer, but relocateAlloc() still works because
  // getOffset() takes care of discontiguous section pieces.
  for (EhInputSection *s : sections)
    s->relocateAlloc(buf, nullptr);

  if (getPartition().ehFrameHdr && getPartition().ehFrameHdr->getParent())
    getPartition().ehFrameHdr->write();
}

GotSection::GotSection()
    : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS, config->wordsize,
                       ".got") {
  // If ElfSym::globalOffsetTable is relative to .got and is referenced,
  // increase numEntries by the number of entries used to emit
  // ElfSym::globalOffsetTable.
  if (ElfSym::globalOffsetTable && !target->gotBaseSymInGotPlt)
    numEntries += target->gotHeaderEntriesNum;
}

void GotSection::addEntry(Symbol &sym) {
  sym.gotIndex = numEntries;
  ++numEntries;
}

bool GotSection::addDynTlsEntry(Symbol &sym) {
  if (sym.globalDynIndex != -1U)
    return false;
  sym.globalDynIndex = numEntries;
  // Global Dynamic TLS entries take two GOT slots.
  numEntries += 2;
  return true;
}

// Reserves TLS entries for a TLS module ID and a TLS block offset.
// In total it takes two GOT slots.
bool GotSection::addTlsIndex() {
  if (tlsIndexOff != uint32_t(-1))
    return false;
  tlsIndexOff = numEntries * config->wordsize;
  numEntries += 2;
  return true;
}

uint64_t GotSection::getGlobalDynAddr(const Symbol &b) const {
  return this->getVA() + b.globalDynIndex * config->wordsize;
}

uint64_t GotSection::getGlobalDynOffset(const Symbol &b) const {
  return b.globalDynIndex * config->wordsize;
}

void GotSection::finalizeContents() {
  size = numEntries * config->wordsize;
}

bool GotSection::isNeeded() const {
  // We need to emit a GOT even if it's empty if there's a relocation that is
  // relative to GOT(such as GOTOFFREL).
  return numEntries || hasGotOffRel;
}

void GotSection::writeTo(uint8_t *buf) {
  // Buf points to the start of this section's buffer,
  // whereas InputSectionBase::relocateAlloc() expects its argument
  // to point to the start of the output section.
  target->writeGotHeader(buf);
  relocateAlloc(buf - outSecOff, buf - outSecOff + size);
}

static uint64_t getMipsPageAddr(uint64_t addr) {
  return (addr + 0x8000) & ~0xffff;
}

static uint64_t getMipsPageCount(uint64_t size) {
  return (size + 0xfffe) / 0xffff + 1;
}

MipsGotSection::MipsGotSection()
    : SyntheticSection(SHF_ALLOC | SHF_WRITE | SHF_MIPS_GPREL, SHT_PROGBITS, 16,
                       ".got") {}

void MipsGotSection::addEntry(InputFile &file, Symbol &sym, int64_t addend,
                              RelExpr expr) {
  FileGot &g = getGot(file);
  if (expr == R_MIPS_GOT_LOCAL_PAGE) {
    if (const OutputSection *os = sym.getOutputSection())
      g.pagesMap.insert({os, {}});
    else
      g.local16.insert({{nullptr, getMipsPageAddr(sym.getVA(addend))}, 0});
  } else if (sym.isTls())
    g.tls.insert({&sym, 0});
  else if (sym.isPreemptible && expr == R_ABS)
    g.relocs.insert({&sym, 0});
  else if (sym.isPreemptible)
    g.global.insert({&sym, 0});
  else if (expr == R_MIPS_GOT_OFF32)
    g.local32.insert({{&sym, addend}, 0});
  else
    g.local16.insert({{&sym, addend}, 0});
}

void MipsGotSection::addDynTlsEntry(InputFile &file, Symbol &sym) {
  getGot(file).dynTlsSymbols.insert({&sym, 0});
}

void MipsGotSection::addTlsIndex(InputFile &file) {
  getGot(file).dynTlsSymbols.insert({nullptr, 0});
}

size_t MipsGotSection::FileGot::getEntriesNum() const {
  return getPageEntriesNum() + local16.size() + global.size() + relocs.size() +
         tls.size() + dynTlsSymbols.size() * 2;
}

size_t MipsGotSection::FileGot::getPageEntriesNum() const {
  size_t num = 0;
  for (const std::pair<const OutputSection *, FileGot::PageBlock> &p : pagesMap)
    num += p.second.count;
  return num;
}

size_t MipsGotSection::FileGot::getIndexedEntriesNum() const {
  size_t count = getPageEntriesNum() + local16.size() + global.size();
  // If there are relocation-only entries in the GOT, TLS entries
  // are allocated after them. TLS entries should be addressable
  // by 16-bit index so count both reloc-only and TLS entries.
  if (!tls.empty() || !dynTlsSymbols.empty())
    count += relocs.size() + tls.size() + dynTlsSymbols.size() * 2;
  return count;
}

MipsGotSection::FileGot &MipsGotSection::getGot(InputFile &f) {
  if (!f.mipsGotIndex.hasValue()) {
    gots.emplace_back();
    gots.back().file = &f;
    f.mipsGotIndex = gots.size() - 1;
  }
  return gots[*f.mipsGotIndex];
}

uint64_t MipsGotSection::getPageEntryOffset(const InputFile *f,
                                            const Symbol &sym,
                                            int64_t addend) const {
  const FileGot &g = gots[*f->mipsGotIndex];
  uint64_t index = 0;
  if (const OutputSection *outSec = sym.getOutputSection()) {
    uint64_t secAddr = getMipsPageAddr(outSec->addr);
    uint64_t symAddr = getMipsPageAddr(sym.getVA(addend));
    index = g.pagesMap.lookup(outSec).firstIndex + (symAddr - secAddr) / 0xffff;
  } else {
    index = g.local16.lookup({nullptr, getMipsPageAddr(sym.getVA(addend))});
  }
  return index * config->wordsize;
}

uint64_t MipsGotSection::getSymEntryOffset(const InputFile *f, const Symbol &s,
                                           int64_t addend) const {
  const FileGot &g = gots[*f->mipsGotIndex];
  Symbol *sym = const_cast<Symbol *>(&s);
  if (sym->isTls())
    return g.tls.lookup(sym) * config->wordsize;
  if (sym->isPreemptible)
    return g.global.lookup(sym) * config->wordsize;
  return g.local16.lookup({sym, addend}) * config->wordsize;
}

uint64_t MipsGotSection::getTlsIndexOffset(const InputFile *f) const {
  const FileGot &g = gots[*f->mipsGotIndex];
  return g.dynTlsSymbols.lookup(nullptr) * config->wordsize;
}

uint64_t MipsGotSection::getGlobalDynOffset(const InputFile *f,
                                            const Symbol &s) const {
  const FileGot &g = gots[*f->mipsGotIndex];
  Symbol *sym = const_cast<Symbol *>(&s);
  return g.dynTlsSymbols.lookup(sym) * config->wordsize;
}

const Symbol *MipsGotSection::getFirstGlobalEntry() const {
  if (gots.empty())
    return nullptr;
  const FileGot &primGot = gots.front();
  if (!primGot.global.empty())
    return primGot.global.front().first;
  if (!primGot.relocs.empty())
    return primGot.relocs.front().first;
  return nullptr;
}

unsigned MipsGotSection::getLocalEntriesNum() const {
  if (gots.empty())
    return headerEntriesNum;
  return headerEntriesNum + gots.front().getPageEntriesNum() +
         gots.front().local16.size();
}

bool MipsGotSection::tryMergeGots(FileGot &dst, FileGot &src, bool isPrimary) {
  FileGot tmp = dst;
  set_union(tmp.pagesMap, src.pagesMap);
  set_union(tmp.local16, src.local16);
  set_union(tmp.global, src.global);
  set_union(tmp.relocs, src.relocs);
  set_union(tmp.tls, src.tls);
  set_union(tmp.dynTlsSymbols, src.dynTlsSymbols);

  size_t count = isPrimary ? headerEntriesNum : 0;
  count += tmp.getIndexedEntriesNum();

  if (count * config->wordsize > config->mipsGotSize)
    return false;

  std::swap(tmp, dst);
  return true;
}

void MipsGotSection::finalizeContents() { updateAllocSize(); }

bool MipsGotSection::updateAllocSize() {
  size = headerEntriesNum * config->wordsize;
  for (const FileGot &g : gots)
    size += g.getEntriesNum() * config->wordsize;
  return false;
}

void MipsGotSection::build() {
  if (gots.empty())
    return;

  std::vector<FileGot> mergedGots(1);

  // For each GOT move non-preemptible symbols from the `Global`
  // to `Local16` list. Preemptible symbol might become non-preemptible
  // one if, for example, it gets a related copy relocation.
  for (FileGot &got : gots) {
    for (auto &p: got.global)
      if (!p.first->isPreemptible)
        got.local16.insert({{p.first, 0}, 0});
    got.global.remove_if([&](const std::pair<Symbol *, size_t> &p) {
      return !p.first->isPreemptible;
    });
  }

  // For each GOT remove "reloc-only" entry if there is "global"
  // entry for the same symbol. And add local entries which indexed
  // using 32-bit value at the end of 16-bit entries.
  for (FileGot &got : gots) {
    got.relocs.remove_if([&](const std::pair<Symbol *, size_t> &p) {
      return got.global.count(p.first);
    });
    set_union(got.local16, got.local32);
    got.local32.clear();
  }

  // Evaluate number of "reloc-only" entries in the resulting GOT.
  // To do that put all unique "reloc-only" and "global" entries
  // from all GOTs to the future primary GOT.
  FileGot *primGot = &mergedGots.front();
  for (FileGot &got : gots) {
    set_union(primGot->relocs, got.global);
    set_union(primGot->relocs, got.relocs);
    got.relocs.clear();
  }

  // Evaluate number of "page" entries in each GOT.
  for (FileGot &got : gots) {
    for (std::pair<const OutputSection *, FileGot::PageBlock> &p :
         got.pagesMap) {
      const OutputSection *os = p.first;
      uint64_t secSize = 0;
      for (BaseCommand *cmd : os->sectionCommands) {
        if (auto *isd = dyn_cast<InputSectionDescription>(cmd))
          for (InputSection *isec : isd->sections) {
            uint64_t off = alignTo(secSize, isec->alignment);
            secSize = off + isec->getSize();
          }
      }
      p.second.count = getMipsPageCount(secSize);
    }
  }

  // Merge GOTs. Try to join as much as possible GOTs but do not exceed
  // maximum GOT size. At first, try to fill the primary GOT because
  // the primary GOT can be accessed in the most effective way. If it
  // is not possible, try to fill the last GOT in the list, and finally
  // create a new GOT if both attempts failed.
  for (FileGot &srcGot : gots) {
    InputFile *file = srcGot.file;
    if (tryMergeGots(mergedGots.front(), srcGot, true)) {
      file->mipsGotIndex = 0;
    } else {
      // If this is the first time we failed to merge with the primary GOT,
      // MergedGots.back() will also be the primary GOT. We must make sure not
      // to try to merge again with isPrimary=false, as otherwise, if the
      // inputs are just right, we could allow the primary GOT to become 1 or 2
      // words bigger due to ignoring the header size.
      if (mergedGots.size() == 1 ||
          !tryMergeGots(mergedGots.back(), srcGot, false)) {
        mergedGots.emplace_back();
        std::swap(mergedGots.back(), srcGot);
      }
      file->mipsGotIndex = mergedGots.size() - 1;
    }
  }
  std::swap(gots, mergedGots);

  // Reduce number of "reloc-only" entries in the primary GOT
  // by substracting "global" entries exist in the primary GOT.
  primGot = &gots.front();
  primGot->relocs.remove_if([&](const std::pair<Symbol *, size_t> &p) {
    return primGot->global.count(p.first);
  });

  // Calculate indexes for each GOT entry.
  size_t index = headerEntriesNum;
  for (FileGot &got : gots) {
    got.startIndex = &got == primGot ? 0 : index;
    for (std::pair<const OutputSection *, FileGot::PageBlock> &p :
         got.pagesMap) {
      // For each output section referenced by GOT page relocations calculate
      // and save into pagesMap an upper bound of MIPS GOT entries required
      // to store page addresses of local symbols. We assume the worst case -
      // each 64kb page of the output section has at least one GOT relocation
      // against it. And take in account the case when the section intersects
      // page boundaries.
      p.second.firstIndex = index;
      index += p.second.count;
    }
    for (auto &p: got.local16)
      p.second = index++;
    for (auto &p: got.global)
      p.second = index++;
    for (auto &p: got.relocs)
      p.second = index++;
    for (auto &p: got.tls)
      p.second = index++;
    for (auto &p: got.dynTlsSymbols) {
      p.second = index;
      index += 2;
    }
  }

  // Update Symbol::gotIndex field to use this
  // value later in the `sortMipsSymbols` function.
  for (auto &p : primGot->global)
    p.first->gotIndex = p.second;
  for (auto &p : primGot->relocs)
    p.first->gotIndex = p.second;

  // Create dynamic relocations.
  for (FileGot &got : gots) {
    // Create dynamic relocations for TLS entries.
    for (std::pair<Symbol *, size_t> &p : got.tls) {
      Symbol *s = p.first;
      uint64_t offset = p.second * config->wordsize;
      if (s->isPreemptible)
        mainPart->relaDyn->addReloc(target->tlsGotRel, this, offset, s);
    }
    for (std::pair<Symbol *, size_t> &p : got.dynTlsSymbols) {
      Symbol *s = p.first;
      uint64_t offset = p.second * config->wordsize;
      if (s == nullptr) {
        if (!config->isPic)
          continue;
        mainPart->relaDyn->addReloc(target->tlsModuleIndexRel, this, offset, s);
      } else {
        // When building a shared library we still need a dynamic relocation
        // for the module index. Therefore only checking for
        // S->isPreemptible is not sufficient (this happens e.g. for
        // thread-locals that have been marked as local through a linker script)
        if (!s->isPreemptible && !config->isPic)
          continue;
        mainPart->relaDyn->addReloc(target->tlsModuleIndexRel, this, offset, s);
        // However, we can skip writing the TLS offset reloc for non-preemptible
        // symbols since it is known even in shared libraries
        if (!s->isPreemptible)
          continue;
        offset += config->wordsize;
        mainPart->relaDyn->addReloc(target->tlsOffsetRel, this, offset, s);
      }
    }

    // Do not create dynamic relocations for non-TLS
    // entries in the primary GOT.
    if (&got == primGot)
      continue;

    // Dynamic relocations for "global" entries.
    for (const std::pair<Symbol *, size_t> &p : got.global) {
      uint64_t offset = p.second * config->wordsize;
      mainPart->relaDyn->addReloc(target->relativeRel, this, offset, p.first);
    }
    if (!config->isPic)
      continue;
    // Dynamic relocations for "local" entries in case of PIC.
    for (const std::pair<const OutputSection *, FileGot::PageBlock> &l :
         got.pagesMap) {
      size_t pageCount = l.second.count;
      for (size_t pi = 0; pi < pageCount; ++pi) {
        uint64_t offset = (l.second.firstIndex + pi) * config->wordsize;
        mainPart->relaDyn->addReloc({target->relativeRel, this, offset, l.first,
                                 int64_t(pi * 0x10000)});
      }
    }
    for (const std::pair<GotEntry, size_t> &p : got.local16) {
      uint64_t offset = p.second * config->wordsize;
      mainPart->relaDyn->addReloc({target->relativeRel, this, offset, true,
                               p.first.first, p.first.second});
    }
  }
}

bool MipsGotSection::isNeeded() const {
  // We add the .got section to the result for dynamic MIPS target because
  // its address and properties are mentioned in the .dynamic section.
  return !config->relocatable;
}

uint64_t MipsGotSection::getGp(const InputFile *f) const {
  // For files without related GOT or files refer a primary GOT
  // returns "common" _gp value. For secondary GOTs calculate
  // individual _gp values.
  if (!f || !f->mipsGotIndex.hasValue() || *f->mipsGotIndex == 0)
    return ElfSym::mipsGp->getVA(0);
  return getVA() + gots[*f->mipsGotIndex].startIndex * config->wordsize +
         0x7ff0;
}

void MipsGotSection::writeTo(uint8_t *buf) {
  // Set the MSB of the second GOT slot. This is not required by any
  // MIPS ABI documentation, though.
  //
  // There is a comment in glibc saying that "The MSB of got[1] of a
  // gnu object is set to identify gnu objects," and in GNU gold it
  // says "the second entry will be used by some runtime loaders".
  // But how this field is being used is unclear.
  //
  // We are not really willing to mimic other linkers behaviors
  // without understanding why they do that, but because all files
  // generated by GNU tools have this special GOT value, and because
  // we've been doing this for years, it is probably a safe bet to
  // keep doing this for now. We really need to revisit this to see
  // if we had to do this.
  writeUint(buf + config->wordsize, (uint64_t)1 << (config->wordsize * 8 - 1));
  for (const FileGot &g : gots) {
    auto write = [&](size_t i, const Symbol *s, int64_t a) {
      uint64_t va = a;
      if (s)
        va = s->getVA(a);
      writeUint(buf + i * config->wordsize, va);
    };
    // Write 'page address' entries to the local part of the GOT.
    for (const std::pair<const OutputSection *, FileGot::PageBlock> &l :
         g.pagesMap) {
      size_t pageCount = l.second.count;
      uint64_t firstPageAddr = getMipsPageAddr(l.first->addr);
      for (size_t pi = 0; pi < pageCount; ++pi)
        write(l.second.firstIndex + pi, nullptr, firstPageAddr + pi * 0x10000);
    }
    // Local, global, TLS, reloc-only  entries.
    // If TLS entry has a corresponding dynamic relocations, leave it
    // initialized by zero. Write down adjusted TLS symbol's values otherwise.
    // To calculate the adjustments use offsets for thread-local storage.
    // https://www.linux-mips.org/wiki/NPTL
    for (const std::pair<GotEntry, size_t> &p : g.local16)
      write(p.second, p.first.first, p.first.second);
    // Write VA to the primary GOT only. For secondary GOTs that
    // will be done by REL32 dynamic relocations.
    if (&g == &gots.front())
      for (const std::pair<const Symbol *, size_t> &p : g.global)
        write(p.second, p.first, 0);
    for (const std::pair<Symbol *, size_t> &p : g.relocs)
      write(p.second, p.first, 0);
    for (const std::pair<Symbol *, size_t> &p : g.tls)
      write(p.second, p.first, p.first->isPreemptible ? 0 : -0x7000);
    for (const std::pair<Symbol *, size_t> &p : g.dynTlsSymbols) {
      if (p.first == nullptr && !config->isPic)
        write(p.second, nullptr, 1);
      else if (p.first && !p.first->isPreemptible) {
        // If we are emitting PIC code with relocations we mustn't write
        // anything to the GOT here. When using Elf_Rel relocations the value
        // one will be treated as an addend and will cause crashes at runtime
        if (!config->isPic)
          write(p.second, nullptr, 1);
        write(p.second + 1, p.first, -0x8000);
      }
    }
  }
}

// On PowerPC the .plt section is used to hold the table of function addresses
// instead of the .got.plt, and the type is SHT_NOBITS similar to a .bss
// section. I don't know why we have a BSS style type for the section but it is
// consitent across both 64-bit PowerPC ABIs as well as the 32-bit PowerPC ABI.
GotPltSection::GotPltSection()
    : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS, config->wordsize,
                       ".got.plt") {
  if (config->emachine == EM_PPC) {
    name = ".plt";
  } else if (config->emachine == EM_PPC64) {
    type = SHT_NOBITS;
    name = ".plt";
  }
}

void GotPltSection::addEntry(Symbol &sym) {
  assert(sym.pltIndex == entries.size());
  entries.push_back(&sym);
}

size_t GotPltSection::getSize() const {
  return (target->gotPltHeaderEntriesNum + entries.size()) * config->wordsize;
}

void GotPltSection::writeTo(uint8_t *buf) {
  target->writeGotPltHeader(buf);
  buf += target->gotPltHeaderEntriesNum * config->wordsize;
  for (const Symbol *b : entries) {
    target->writeGotPlt(buf, *b);
    buf += config->wordsize;
  }
}

bool GotPltSection::isNeeded() const {
  // We need to emit GOTPLT even if it's empty if there's a relocation relative
  // to it.
  return !entries.empty() || hasGotPltOffRel;
}

static StringRef getIgotPltName() {
  // On ARM the IgotPltSection is part of the GotSection.
  if (config->emachine == EM_ARM)
    return ".got";

  // On PowerPC64 the GotPltSection is renamed to '.plt' so the IgotPltSection
  // needs to be named the same.
  if (config->emachine == EM_PPC64)
    return ".plt";

  return ".got.plt";
}

// On PowerPC64 the GotPltSection type is SHT_NOBITS so we have to follow suit
// with the IgotPltSection.
IgotPltSection::IgotPltSection()
    : SyntheticSection(SHF_ALLOC | SHF_WRITE,
                       config->emachine == EM_PPC64 ? SHT_NOBITS : SHT_PROGBITS,
                       config->wordsize, getIgotPltName()) {}

void IgotPltSection::addEntry(Symbol &sym) {
  assert(sym.pltIndex == entries.size());
  entries.push_back(&sym);
}

size_t IgotPltSection::getSize() const {
  return entries.size() * config->wordsize;
}

void IgotPltSection::writeTo(uint8_t *buf) {
  for (const Symbol *b : entries) {
    target->writeIgotPlt(buf, *b);
    buf += config->wordsize;
  }
}

StringTableSection::StringTableSection(StringRef name, bool dynamic)
    : SyntheticSection(dynamic ? (uint64_t)SHF_ALLOC : 0, SHT_STRTAB, 1, name),
      dynamic(dynamic) {
  // ELF string tables start with a NUL byte.
  addString("");
}

// Adds a string to the string table. If `hashIt` is true we hash and check for
// duplicates. It is optional because the name of global symbols are already
// uniqued and hashing them again has a big cost for a small value: uniquing
// them with some other string that happens to be the same.
unsigned StringTableSection::addString(StringRef s, bool hashIt) {
  if (hashIt) {
    auto r = stringMap.insert(std::make_pair(s, this->size));
    if (!r.second)
      return r.first->second;
  }
  unsigned ret = this->size;
  this->size = this->size + s.size() + 1;
  strings.push_back(s);
  return ret;
}

void StringTableSection::writeTo(uint8_t *buf) {
  for (StringRef s : strings) {
    memcpy(buf, s.data(), s.size());
    buf[s.size()] = '\0';
    buf += s.size() + 1;
  }
}

// Returns the number of version definition entries. Because the first entry
// is for the version definition itself, it is the number of versioned symbols
// plus one. Note that we don't support multiple versions yet.
static unsigned getVerDefNum() { return config->versionDefinitions.size() + 1; }

template <class ELFT>
DynamicSection<ELFT>::DynamicSection()
    : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_DYNAMIC, config->wordsize,
                       ".dynamic") {
  this->entsize = ELFT::Is64Bits ? 16 : 8;

  // .dynamic section is not writable on MIPS and on Fuchsia OS
  // which passes -z rodynamic.
  // See "Special Section" in Chapter 4 in the following document:
  // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
  if (config->emachine == EM_MIPS || config->zRodynamic)
    this->flags = SHF_ALLOC;
}

template <class ELFT>
void DynamicSection<ELFT>::add(int32_t tag, std::function<uint64_t()> fn) {
  entries.push_back({tag, fn});
}

template <class ELFT>
void DynamicSection<ELFT>::addInt(int32_t tag, uint64_t val) {
  entries.push_back({tag, [=] { return val; }});
}

template <class ELFT>
void DynamicSection<ELFT>::addInSec(int32_t tag, InputSection *sec) {
  entries.push_back({tag, [=] { return sec->getVA(0); }});
}

template <class ELFT>
void DynamicSection<ELFT>::addInSecRelative(int32_t tag, InputSection *sec) {
  size_t tagOffset = entries.size() * entsize;
  entries.push_back(
      {tag, [=] { return sec->getVA(0) - (getVA() + tagOffset); }});
}

template <class ELFT>
void DynamicSection<ELFT>::addOutSec(int32_t tag, OutputSection *sec) {
  entries.push_back({tag, [=] { return sec->addr; }});
}

template <class ELFT>
void DynamicSection<ELFT>::addSize(int32_t tag, OutputSection *sec) {
  entries.push_back({tag, [=] { return sec->size; }});
}

template <class ELFT>
void DynamicSection<ELFT>::addSym(int32_t tag, Symbol *sym) {
  entries.push_back({tag, [=] { return sym->getVA(); }});
}

// A Linker script may assign the RELA relocation sections to the same
// output section. When this occurs we cannot just use the OutputSection
// Size. Moreover the [DT_JMPREL, DT_JMPREL + DT_PLTRELSZ) is permitted to
// overlap with the [DT_RELA, DT_RELA + DT_RELASZ).
static uint64_t addPltRelSz() {
  size_t size = in.relaPlt->getSize();
  if (in.relaIplt->getParent() == in.relaPlt->getParent() &&
      in.relaIplt->name == in.relaPlt->name)
    size += in.relaIplt->getSize();
  return size;
}

// Add remaining entries to complete .dynamic contents.
template <class ELFT> void DynamicSection<ELFT>::finalizeContents() {
  elf::Partition &part = getPartition();
  bool isMain = part.name.empty();

  for (StringRef s : config->filterList)
    addInt(DT_FILTER, part.dynStrTab->addString(s));
  for (StringRef s : config->auxiliaryList)
    addInt(DT_AUXILIARY, part.dynStrTab->addString(s));

  if (!config->rpath.empty())
    addInt(config->enableNewDtags ? DT_RUNPATH : DT_RPATH,
           part.dynStrTab->addString(config->rpath));

  for (SharedFile *file : sharedFiles)
    if (file->isNeeded)
      addInt(DT_NEEDED, part.dynStrTab->addString(file->soName));

  if (isMain) {
    if (!config->soName.empty())
      addInt(DT_SONAME, part.dynStrTab->addString(config->soName));
  } else {
    if (!config->soName.empty())
      addInt(DT_NEEDED, part.dynStrTab->addString(config->soName));
    addInt(DT_SONAME, part.dynStrTab->addString(part.name));
  }

  // Set DT_FLAGS and DT_FLAGS_1.
  uint32_t dtFlags = 0;
  uint32_t dtFlags1 = 0;
  if (config->bsymbolic)
    dtFlags |= DF_SYMBOLIC;
  if (config->zGlobal)
    dtFlags1 |= DF_1_GLOBAL;
  if (config->zInitfirst)
    dtFlags1 |= DF_1_INITFIRST;
  if (config->zInterpose)
    dtFlags1 |= DF_1_INTERPOSE;
  if (config->zNodefaultlib)
    dtFlags1 |= DF_1_NODEFLIB;
  if (config->zNodelete)
    dtFlags1 |= DF_1_NODELETE;
  if (config->zNodlopen)
    dtFlags1 |= DF_1_NOOPEN;
  if (config->zNow) {
    dtFlags |= DF_BIND_NOW;
    dtFlags1 |= DF_1_NOW;
  }
  if (config->zOrigin) {
    dtFlags |= DF_ORIGIN;
    dtFlags1 |= DF_1_ORIGIN;
  }
  if (!config->zText)
    dtFlags |= DF_TEXTREL;
  if (config->hasStaticTlsModel)
    dtFlags |= DF_STATIC_TLS;

  if (dtFlags)
    addInt(DT_FLAGS, dtFlags);
  if (dtFlags1)
    addInt(DT_FLAGS_1, dtFlags1);

  // DT_DEBUG is a pointer to debug informaion used by debuggers at runtime. We
  // need it for each process, so we don't write it for DSOs. The loader writes
  // the pointer into this entry.
  //
  // DT_DEBUG is the only .dynamic entry that needs to be written to. Some
  // systems (currently only Fuchsia OS) provide other means to give the
  // debugger this information. Such systems may choose make .dynamic read-only.
  // If the target is such a system (used -z rodynamic) don't write DT_DEBUG.
  if (!config->shared && !config->relocatable && !config->zRodynamic)
    addInt(DT_DEBUG, 0);

  if (OutputSection *sec = part.dynStrTab->getParent())
    this->link = sec->sectionIndex;

  if (part.relaDyn->isNeeded()) {
    addInSec(part.relaDyn->dynamicTag, part.relaDyn);
    addSize(part.relaDyn->sizeDynamicTag, part.relaDyn->getParent());

    bool isRela = config->isRela;
    addInt(isRela ? DT_RELAENT : DT_RELENT,
           isRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel));

    // MIPS dynamic loader does not support RELCOUNT tag.
    // The problem is in the tight relation between dynamic
    // relocations and GOT. So do not emit this tag on MIPS.
    if (config->emachine != EM_MIPS) {
      size_t numRelativeRels = part.relaDyn->getRelativeRelocCount();
      if (config->zCombreloc && numRelativeRels)
        addInt(isRela ? DT_RELACOUNT : DT_RELCOUNT, numRelativeRels);
    }
  }
  if (part.relrDyn && !part.relrDyn->relocs.empty()) {
    addInSec(config->useAndroidRelrTags ? DT_ANDROID_RELR : DT_RELR,
             part.relrDyn);
    addSize(config->useAndroidRelrTags ? DT_ANDROID_RELRSZ : DT_RELRSZ,
            part.relrDyn->getParent());
    addInt(config->useAndroidRelrTags ? DT_ANDROID_RELRENT : DT_RELRENT,
           sizeof(Elf_Relr));
  }
  // .rel[a].plt section usually consists of two parts, containing plt and
  // iplt relocations. It is possible to have only iplt relocations in the
  // output. In that case relaPlt is empty and have zero offset, the same offset
  // as relaIplt has. And we still want to emit proper dynamic tags for that
  // case, so here we always use relaPlt as marker for the begining of
  // .rel[a].plt section.
  if (isMain && (in.relaPlt->isNeeded() || in.relaIplt->isNeeded())) {
    addInSec(DT_JMPREL, in.relaPlt);
    entries.push_back({DT_PLTRELSZ, addPltRelSz});
    switch (config->emachine) {
    case EM_MIPS:
      addInSec(DT_MIPS_PLTGOT, in.gotPlt);
      break;
    case EM_SPARCV9:
      addInSec(DT_PLTGOT, in.plt);
      break;
    default:
      addInSec(DT_PLTGOT, in.gotPlt);
      break;
    }
    addInt(DT_PLTREL, config->isRela ? DT_RELA : DT_REL);
  }

  if (config->emachine == EM_AARCH64) {
    if (config->andFeatures & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)
      addInt(DT_AARCH64_BTI_PLT, 0);
    if (config->andFeatures & GNU_PROPERTY_AARCH64_FEATURE_1_PAC)
      addInt(DT_AARCH64_PAC_PLT, 0);
  }

  addInSec(DT_SYMTAB, part.dynSymTab);
  addInt(DT_SYMENT, sizeof(Elf_Sym));
  addInSec(DT_STRTAB, part.dynStrTab);
  addInt(DT_STRSZ, part.dynStrTab->getSize());
  if (!config->zText)
    addInt(DT_TEXTREL, 0);
  if (part.gnuHashTab)
    addInSec(DT_GNU_HASH, part.gnuHashTab);
  if (part.hashTab)
    addInSec(DT_HASH, part.hashTab);

  if (isMain) {
    if (Out::preinitArray) {
      addOutSec(DT_PREINIT_ARRAY, Out::preinitArray);
      addSize(DT_PREINIT_ARRAYSZ, Out::preinitArray);
    }
    if (Out::initArray) {
      addOutSec(DT_INIT_ARRAY, Out::initArray);
      addSize(DT_INIT_ARRAYSZ, Out::initArray);
    }
    if (Out::finiArray) {
      addOutSec(DT_FINI_ARRAY, Out::finiArray);
      addSize(DT_FINI_ARRAYSZ, Out::finiArray);
    }

    if (Symbol *b = symtab->find(config->init))
      if (b->isDefined())
        addSym(DT_INIT, b);
    if (Symbol *b = symtab->find(config->fini))
      if (b->isDefined())
        addSym(DT_FINI, b);
  }

  bool hasVerNeed = SharedFile::vernauxNum != 0;
  if (hasVerNeed || part.verDef)
    addInSec(DT_VERSYM, part.verSym);
  if (part.verDef) {
    addInSec(DT_VERDEF, part.verDef);
    addInt(DT_VERDEFNUM, getVerDefNum());
  }
  if (hasVerNeed) {
    addInSec(DT_VERNEED, part.verNeed);
    unsigned needNum = 0;
    for (SharedFile *f : sharedFiles)
      if (!f->vernauxs.empty())
        ++needNum;
    addInt(DT_VERNEEDNUM, needNum);
  }

  if (config->emachine == EM_MIPS) {
    addInt(DT_MIPS_RLD_VERSION, 1);
    addInt(DT_MIPS_FLAGS, RHF_NOTPOT);
    addInt(DT_MIPS_BASE_ADDRESS, target->getImageBase());
    addInt(DT_MIPS_SYMTABNO, part.dynSymTab->getNumSymbols());

    add(DT_MIPS_LOCAL_GOTNO, [] { return in.mipsGot->getLocalEntriesNum(); });

    if (const Symbol *b = in.mipsGot->getFirstGlobalEntry())
      addInt(DT_MIPS_GOTSYM, b->dynsymIndex);
    else
      addInt(DT_MIPS_GOTSYM, part.dynSymTab->getNumSymbols());
    addInSec(DT_PLTGOT, in.mipsGot);
    if (in.mipsRldMap) {
      if (!config->pie)
        addInSec(DT_MIPS_RLD_MAP, in.mipsRldMap);
      // Store the offset to the .rld_map section
      // relative to the address of the tag.
      addInSecRelative(DT_MIPS_RLD_MAP_REL, in.mipsRldMap);
    }
  }

  // DT_PPC_GOT indicates to glibc Secure PLT is used. If DT_PPC_GOT is absent,
  // glibc assumes the old-style BSS PLT layout which we don't support.
  if (config->emachine == EM_PPC)
    add(DT_PPC_GOT, [] { return in.got->getVA(); });

  // Glink dynamic tag is required by the V2 abi if the plt section isn't empty.
  if (config->emachine == EM_PPC64 && in.plt->isNeeded()) {
    // The Glink tag points to 32 bytes before the first lazy symbol resolution
    // stub, which starts directly after the header.
    entries.push_back({DT_PPC64_GLINK, [=] {
                         unsigned offset = target->pltHeaderSize - 32;
                         return in.plt->getVA(0) + offset;
                       }});
  }

  addInt(DT_NULL, 0);

  getParent()->link = this->link;
  this->size = entries.size() * this->entsize;
}

template <class ELFT> void DynamicSection<ELFT>::writeTo(uint8_t *buf) {
  auto *p = reinterpret_cast<Elf_Dyn *>(buf);

  for (std::pair<int32_t, std::function<uint64_t()>> &kv : entries) {
    p->d_tag = kv.first;
    p->d_un.d_val = kv.second();
    ++p;
  }
}

uint64_t DynamicReloc::getOffset() const {
  return inputSec->getVA(offsetInSec);
}

int64_t DynamicReloc::computeAddend() const {
  if (useSymVA)
    return sym->getVA(addend);
  if (!outputSec)
    return addend;
  // See the comment in the DynamicReloc ctor.
  return getMipsPageAddr(outputSec->addr) + addend;
}

uint32_t DynamicReloc::getSymIndex(SymbolTableBaseSection *symTab) const {
  if (sym && !useSymVA)
    return symTab->getSymbolIndex(sym);
  return 0;
}

RelocationBaseSection::RelocationBaseSection(StringRef name, uint32_t type,
                                             int32_t dynamicTag,
                                             int32_t sizeDynamicTag)
    : SyntheticSection(SHF_ALLOC, type, config->wordsize, name),
      dynamicTag(dynamicTag), sizeDynamicTag(sizeDynamicTag) {}

void RelocationBaseSection::addReloc(RelType dynType, InputSectionBase *isec,
                                     uint64_t offsetInSec, Symbol *sym) {
  addReloc({dynType, isec, offsetInSec, false, sym, 0});
}

void RelocationBaseSection::addReloc(RelType dynType,
                                     InputSectionBase *inputSec,
                                     uint64_t offsetInSec, Symbol *sym,
                                     int64_t addend, RelExpr expr,
                                     RelType type) {
  // Write the addends to the relocated address if required. We skip
  // it if the written value would be zero.
  if (config->writeAddends && (expr != R_ADDEND || addend != 0))
    inputSec->relocations.push_back({expr, type, offsetInSec, addend, sym});
  addReloc({dynType, inputSec, offsetInSec, expr != R_ADDEND, sym, addend});
}

void RelocationBaseSection::addReloc(const DynamicReloc &reloc) {
  if (reloc.type == target->relativeRel)
    ++numRelativeRelocs;
  relocs.push_back(reloc);
}

void RelocationBaseSection::finalizeContents() {
  SymbolTableBaseSection *symTab = getPartition().dynSymTab;

  // When linking glibc statically, .rel{,a}.plt contains R_*_IRELATIVE
  // relocations due to IFUNC (e.g. strcpy). sh_link will be set to 0 in that
  // case.
  if (symTab && symTab->getParent())
    getParent()->link = symTab->getParent()->sectionIndex;
  else
    getParent()->link = 0;

  if (in.relaPlt == this)
    getParent()->info = in.gotPlt->getParent()->sectionIndex;
  if (in.relaIplt == this)
    getParent()->info = in.igotPlt->getParent()->sectionIndex;
}

RelrBaseSection::RelrBaseSection()
    : SyntheticSection(SHF_ALLOC,
                       config->useAndroidRelrTags ? SHT_ANDROID_RELR : SHT_RELR,
                       config->wordsize, ".relr.dyn") {}

template <class ELFT>
static void encodeDynamicReloc(SymbolTableBaseSection *symTab,
                               typename ELFT::Rela *p,
                               const DynamicReloc &rel) {
  if (config->isRela)
    p->r_addend = rel.computeAddend();
  p->r_offset = rel.getOffset();
  p->setSymbolAndType(rel.getSymIndex(symTab), rel.type, config->isMips64EL);
}

template <class ELFT>
RelocationSection<ELFT>::RelocationSection(StringRef name, bool sort)
    : RelocationBaseSection(name, config->isRela ? SHT_RELA : SHT_REL,
                            config->isRela ? DT_RELA : DT_REL,
                            config->isRela ? DT_RELASZ : DT_RELSZ),
      sort(sort) {
  this->entsize = config->isRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
}

template <class ELFT> void RelocationSection<ELFT>::writeTo(uint8_t *buf) {
  SymbolTableBaseSection *symTab = getPartition().dynSymTab;

  // Sort by (!IsRelative,SymIndex,r_offset). DT_REL[A]COUNT requires us to
  // place R_*_RELATIVE first. SymIndex is to improve locality, while r_offset
  // is to make results easier to read.
  if (sort)
    llvm::stable_sort(
        relocs, [&](const DynamicReloc &a, const DynamicReloc &b) {
          return std::make_tuple(a.type != target->relativeRel,
                                 a.getSymIndex(symTab), a.getOffset()) <
                 std::make_tuple(b.type != target->relativeRel,
                                 b.getSymIndex(symTab), b.getOffset());
        });

  for (const DynamicReloc &rel : relocs) {
    encodeDynamicReloc<ELFT>(symTab, reinterpret_cast<Elf_Rela *>(buf), rel);
    buf += config->isRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
  }
}

template <class ELFT>
AndroidPackedRelocationSection<ELFT>::AndroidPackedRelocationSection(
    StringRef name)
    : RelocationBaseSection(
          name, config->isRela ? SHT_ANDROID_RELA : SHT_ANDROID_REL,
          config->isRela ? DT_ANDROID_RELA : DT_ANDROID_REL,
          config->isRela ? DT_ANDROID_RELASZ : DT_ANDROID_RELSZ) {
  this->entsize = 1;
}

template <class ELFT>
bool AndroidPackedRelocationSection<ELFT>::updateAllocSize() {
  // This function computes the contents of an Android-format packed relocation
  // section.
  //
  // This format compresses relocations by using relocation groups to factor out
  // fields that are common between relocations and storing deltas from previous
  // relocations in SLEB128 format (which has a short representation for small
  // numbers). A good example of a relocation type with common fields is
  // R_*_RELATIVE, which is normally used to represent function pointers in
  // vtables. In the REL format, each relative relocation has the same r_info
  // field, and is only different from other relative relocations in terms of
  // the r_offset field. By sorting relocations by offset, grouping them by
  // r_info and representing each relocation with only the delta from the
  // previous offset, each 8-byte relocation can be compressed to as little as 1
  // byte (or less with run-length encoding). This relocation packer was able to
  // reduce the size of the relocation section in an Android Chromium DSO from
  // 2,911,184 bytes to 174,693 bytes, or 6% of the original size.
  //
  // A relocation section consists of a header containing the literal bytes
  // 'APS2' followed by a sequence of SLEB128-encoded integers. The first two
  // elements are the total number of relocations in the section and an initial
  // r_offset value. The remaining elements define a sequence of relocation
  // groups. Each relocation group starts with a header consisting of the
  // following elements:
  //
  // - the number of relocations in the relocation group
  // - flags for the relocation group
  // - (if RELOCATION_GROUPED_BY_OFFSET_DELTA_FLAG is set) the r_offset delta
  //   for each relocation in the group.
  // - (if RELOCATION_GROUPED_BY_INFO_FLAG is set) the value of the r_info
  //   field for each relocation in the group.
  // - (if RELOCATION_GROUP_HAS_ADDEND_FLAG and
  //   RELOCATION_GROUPED_BY_ADDEND_FLAG are set) the r_addend delta for
  //   each relocation in the group.
  //
  // Following the relocation group header are descriptions of each of the
  // relocations in the group. They consist of the following elements:
  //
  // - (if RELOCATION_GROUPED_BY_OFFSET_DELTA_FLAG is not set) the r_offset
  //   delta for this relocation.
  // - (if RELOCATION_GROUPED_BY_INFO_FLAG is not set) the value of the r_info
  //   field for this relocation.
  // - (if RELOCATION_GROUP_HAS_ADDEND_FLAG is set and
  //   RELOCATION_GROUPED_BY_ADDEND_FLAG is not set) the r_addend delta for
  //   this relocation.

  size_t oldSize = relocData.size();

  relocData = {'A', 'P', 'S', '2'};
  raw_svector_ostream os(relocData);
  auto add = [&](int64_t v) { encodeSLEB128(v, os); };

  // The format header includes the number of relocations and the initial
  // offset (we set this to zero because the first relocation group will
  // perform the initial adjustment).
  add(relocs.size());
  add(0);

  std::vector<Elf_Rela> relatives, nonRelatives;

  for (const DynamicReloc &rel : relocs) {
    Elf_Rela r;
    encodeDynamicReloc<ELFT>(getPartition().dynSymTab, &r, rel);

    if (r.getType(config->isMips64EL) == target->relativeRel)
      relatives.push_back(r);
    else
      nonRelatives.push_back(r);
  }

  llvm::sort(relatives, [](const Elf_Rel &a, const Elf_Rel &b) {
    return a.r_offset < b.r_offset;
  });

  // Try to find groups of relative relocations which are spaced one word
  // apart from one another. These generally correspond to vtable entries. The
  // format allows these groups to be encoded using a sort of run-length
  // encoding, but each group will cost 7 bytes in addition to the offset from
  // the previous group, so it is only profitable to do this for groups of
  // size 8 or larger.
  std::vector<Elf_Rela> ungroupedRelatives;
  std::vector<std::vector<Elf_Rela>> relativeGroups;
  for (auto i = relatives.begin(), e = relatives.end(); i != e;) {
    std::vector<Elf_Rela> group;
    do {
      group.push_back(*i++);
    } while (i != e && (i - 1)->r_offset + config->wordsize == i->r_offset);

    if (group.size() < 8)
      ungroupedRelatives.insert(ungroupedRelatives.end(), group.begin(),
                                group.end());
    else
      relativeGroups.emplace_back(std::move(group));
  }

  unsigned hasAddendIfRela =
      config->isRela ? RELOCATION_GROUP_HAS_ADDEND_FLAG : 0;

  uint64_t offset = 0;
  uint64_t addend = 0;

  // Emit the run-length encoding for the groups of adjacent relative
  // relocations. Each group is represented using two groups in the packed
  // format. The first is used to set the current offset to the start of the
  // group (and also encodes the first relocation), and the second encodes the
  // remaining relocations.
  for (std::vector<Elf_Rela> &g : relativeGroups) {
    // The first relocation in the group.
    add(1);
    add(RELOCATION_GROUPED_BY_OFFSET_DELTA_FLAG |
        RELOCATION_GROUPED_BY_INFO_FLAG | hasAddendIfRela);
    add(g[0].r_offset - offset);
    add(target->relativeRel);
    if (config->isRela) {
      add(g[0].r_addend - addend);
      addend = g[0].r_addend;
    }

    // The remaining relocations.
    add(g.size() - 1);
    add(RELOCATION_GROUPED_BY_OFFSET_DELTA_FLAG |
        RELOCATION_GROUPED_BY_INFO_FLAG | hasAddendIfRela);
    add(config->wordsize);
    add(target->relativeRel);
    if (config->isRela) {
      for (auto i = g.begin() + 1, e = g.end(); i != e; ++i) {
        add(i->r_addend - addend);
        addend = i->r_addend;
      }
    }

    offset = g.back().r_offset;
  }

  // Now the ungrouped relatives.
  if (!ungroupedRelatives.empty()) {
    add(ungroupedRelatives.size());
    add(RELOCATION_GROUPED_BY_INFO_FLAG | hasAddendIfRela);
    add(target->relativeRel);
    for (Elf_Rela &r : ungroupedRelatives) {
      add(r.r_offset - offset);
      offset = r.r_offset;
      if (config->isRela) {
        add(r.r_addend - addend);
        addend = r.r_addend;
      }
    }
  }

  // Finally the non-relative relocations.
  llvm::sort(nonRelatives, [](const Elf_Rela &a, const Elf_Rela &b) {
    return a.r_offset < b.r_offset;
  });
  if (!nonRelatives.empty()) {
    add(nonRelatives.size());
    add(hasAddendIfRela);
    for (Elf_Rela &r : nonRelatives) {
      add(r.r_offset - offset);
      offset = r.r_offset;
      add(r.r_info);
      if (config->isRela) {
        add(r.r_addend - addend);
        addend = r.r_addend;
      }
    }
  }

  // Don't allow the section to shrink; otherwise the size of the section can
  // oscillate infinitely.
  if (relocData.size() < oldSize)
    relocData.append(oldSize - relocData.size(), 0);

  // Returns whether the section size changed. We need to keep recomputing both
  // section layout and the contents of this section until the size converges
  // because changing this section's size can affect section layout, which in
  // turn can affect the sizes of the LEB-encoded integers stored in this
  // section.
  return relocData.size() != oldSize;
}

template <class ELFT> RelrSection<ELFT>::RelrSection() {
  this->entsize = config->wordsize;
}

template <class ELFT> bool RelrSection<ELFT>::updateAllocSize() {
  // This function computes the contents of an SHT_RELR packed relocation
  // section.
  //
  // Proposal for adding SHT_RELR sections to generic-abi is here:
  //   https://groups.google.com/forum/#!topic/generic-abi/bX460iggiKg
  //
  // The encoded sequence of Elf64_Relr entries in a SHT_RELR section looks
  // like [ AAAAAAAA BBBBBBB1 BBBBBBB1 ... AAAAAAAA BBBBBB1 ... ]
  //
  // i.e. start with an address, followed by any number of bitmaps. The address
  // entry encodes 1 relocation. The subsequent bitmap entries encode up to 63
  // relocations each, at subsequent offsets following the last address entry.
  //
  // The bitmap entries must have 1 in the least significant bit. The assumption
  // here is that an address cannot have 1 in lsb. Odd addresses are not
  // supported.
  //
  // Excluding the least significant bit in the bitmap, each non-zero bit in
  // the bitmap represents a relocation to be applied to a corresponding machine
  // word that follows the base address word. The second least significant bit
  // represents the machine word immediately following the initial address, and
  // each bit that follows represents the next word, in linear order. As such,
  // a single bitmap can encode up to 31 relocations in a 32-bit object, and
  // 63 relocations in a 64-bit object.
  //
  // This encoding has a couple of interesting properties:
  // 1. Looking at any entry, it is clear whether it's an address or a bitmap:
  //    even means address, odd means bitmap.
  // 2. Just a simple list of addresses is a valid encoding.

  size_t oldSize = relrRelocs.size();
  relrRelocs.clear();

  // Same as Config->Wordsize but faster because this is a compile-time
  // constant.
  const size_t wordsize = sizeof(typename ELFT::uint);

  // Number of bits to use for the relocation offsets bitmap.
  // Must be either 63 or 31.
  const size_t nBits = wordsize * 8 - 1;

  // Get offsets for all relative relocations and sort them.
  std::vector<uint64_t> offsets;
  for (const RelativeReloc &rel : relocs)
    offsets.push_back(rel.getOffset());
  llvm::sort(offsets);

  // For each leading relocation, find following ones that can be folded
  // as a bitmap and fold them.
  for (size_t i = 0, e = offsets.size(); i < e;) {
    // Add a leading relocation.
    relrRelocs.push_back(Elf_Relr(offsets[i]));
    uint64_t base = offsets[i] + wordsize;
    ++i;

    // Find foldable relocations to construct bitmaps.
    while (i < e) {
      uint64_t bitmap = 0;

      while (i < e) {
        uint64_t delta = offsets[i] - base;

        // If it is too far, it cannot be folded.
        if (delta >= nBits * wordsize)
          break;

        // If it is not a multiple of wordsize away, it cannot be folded.
        if (delta % wordsize)
          break;

        // Fold it.
        bitmap |= 1ULL << (delta / wordsize);
        ++i;
      }

      if (!bitmap)
        break;

      relrRelocs.push_back(Elf_Relr((bitmap << 1) | 1));
      base += nBits * wordsize;
    }
  }

  return relrRelocs.size() != oldSize;
}

SymbolTableBaseSection::SymbolTableBaseSection(StringTableSection &strTabSec)
    : SyntheticSection(strTabSec.isDynamic() ? (uint64_t)SHF_ALLOC : 0,
                       strTabSec.isDynamic() ? SHT_DYNSYM : SHT_SYMTAB,
                       config->wordsize,
                       strTabSec.isDynamic() ? ".dynsym" : ".symtab"),
      strTabSec(strTabSec) {}

// Orders symbols according to their positions in the GOT,
// in compliance with MIPS ABI rules.
// See "Global Offset Table" in Chapter 5 in the following document
// for detailed description:
// ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
static bool sortMipsSymbols(const SymbolTableEntry &l,
                            const SymbolTableEntry &r) {
  // Sort entries related to non-local preemptible symbols by GOT indexes.
  // All other entries go to the beginning of a dynsym in arbitrary order.
  if (l.sym->isInGot() && r.sym->isInGot())
    return l.sym->gotIndex < r.sym->gotIndex;
  if (!l.sym->isInGot() && !r.sym->isInGot())
    return false;
  return !l.sym->isInGot();
}

void SymbolTableBaseSection::finalizeContents() {
  if (OutputSection *sec = strTabSec.getParent())
    getParent()->link = sec->sectionIndex;

  if (this->type != SHT_DYNSYM) {
    sortSymTabSymbols();
    return;
  }

  // If it is a .dynsym, there should be no local symbols, but we need
  // to do a few things for the dynamic linker.

  // Section's Info field has the index of the first non-local symbol.
  // Because the first symbol entry is a null entry, 1 is the first.
  getParent()->info = 1;

  if (getPartition().gnuHashTab) {
    // NB: It also sorts Symbols to meet the GNU hash table requirements.
    getPartition().gnuHashTab->addSymbols(symbols);
  } else if (config->emachine == EM_MIPS) {
    llvm::stable_sort(symbols, sortMipsSymbols);
  }

  // Only the main partition's dynsym indexes are stored in the symbols
  // themselves. All other partitions use a lookup table.
  if (this == mainPart->dynSymTab) {
    size_t i = 0;
    for (const SymbolTableEntry &s : symbols)
      s.sym->dynsymIndex = ++i;
  }
}

// The ELF spec requires that all local symbols precede global symbols, so we
// sort symbol entries in this function. (For .dynsym, we don't do that because
// symbols for dynamic linking are inherently all globals.)
//
// Aside from above, we put local symbols in groups starting with the STT_FILE
// symbol. That is convenient for purpose of identifying where are local symbols
// coming from.
void SymbolTableBaseSection::sortSymTabSymbols() {
  // Move all local symbols before global symbols.
  auto e = std::stable_partition(
      symbols.begin(), symbols.end(), [](const SymbolTableEntry &s) {
        return s.sym->isLocal() || s.sym->computeBinding() == STB_LOCAL;
      });
  size_t numLocals = e - symbols.begin();
  getParent()->info = numLocals + 1;

  // We want to group the local symbols by file. For that we rebuild the local
  // part of the symbols vector. We do not need to care about the STT_FILE
  // symbols, they are already naturally placed first in each group. That
  // happens because STT_FILE is always the first symbol in the object and hence
  // precede all other local symbols we add for a file.
  MapVector<InputFile *, std::vector<SymbolTableEntry>> arr;
  for (const SymbolTableEntry &s : llvm::make_range(symbols.begin(), e))
    arr[s.sym->file].push_back(s);

  auto i = symbols.begin();
  for (std::pair<InputFile *, std::vector<SymbolTableEntry>> &p : arr)
    for (SymbolTableEntry &entry : p.second)
      *i++ = entry;
}

void SymbolTableBaseSection::addSymbol(Symbol *b) {
  // Adding a local symbol to a .dynsym is a bug.
  assert(this->type != SHT_DYNSYM || !b->isLocal());

  bool hashIt = b->isLocal();
  symbols.push_back({b, strTabSec.addString(b->getName(), hashIt)});
}

size_t SymbolTableBaseSection::getSymbolIndex(Symbol *sym) {
  if (this == mainPart->dynSymTab)
    return sym->dynsymIndex;

  // Initializes symbol lookup tables lazily. This is used only for -r,
  // -emit-relocs and dynsyms in partitions other than the main one.
  llvm::call_once(onceFlag, [&] {
    symbolIndexMap.reserve(symbols.size());
    size_t i = 0;
    for (const SymbolTableEntry &e : symbols) {
      if (e.sym->type == STT_SECTION)
        sectionIndexMap[e.sym->getOutputSection()] = ++i;
      else
        symbolIndexMap[e.sym] = ++i;
    }
  });

  // Section symbols are mapped based on their output sections
  // to maintain their semantics.
  if (sym->type == STT_SECTION)
    return sectionIndexMap.lookup(sym->getOutputSection());
  return symbolIndexMap.lookup(sym);
}

template <class ELFT>
SymbolTableSection<ELFT>::SymbolTableSection(StringTableSection &strTabSec)
    : SymbolTableBaseSection(strTabSec) {
  this->entsize = sizeof(Elf_Sym);
}

static BssSection *getCommonSec(Symbol *sym) {
  if (!config->defineCommon)
    if (auto *d = dyn_cast<Defined>(sym))
      return dyn_cast_or_null<BssSection>(d->section);
  return nullptr;
}

static uint32_t getSymSectionIndex(Symbol *sym) {
  if (getCommonSec(sym))
    return SHN_COMMON;
  if (!isa<Defined>(sym) || sym->needsPltAddr)
    return SHN_UNDEF;
  if (const OutputSection *os = sym->getOutputSection())
    return os->sectionIndex >= SHN_LORESERVE ? (uint32_t)SHN_XINDEX
                                             : os->sectionIndex;
  return SHN_ABS;
}

// Write the internal symbol table contents to the output symbol table.
template <class ELFT> void SymbolTableSection<ELFT>::writeTo(uint8_t *buf) {
  // The first entry is a null entry as per the ELF spec.
  memset(buf, 0, sizeof(Elf_Sym));
  buf += sizeof(Elf_Sym);

  auto *eSym = reinterpret_cast<Elf_Sym *>(buf);

  for (SymbolTableEntry &ent : symbols) {
    Symbol *sym = ent.sym;
    bool isDefinedHere = type == SHT_SYMTAB || sym->partition == partition;

    // Set st_info and st_other.
    eSym->st_other = 0;
    if (sym->isLocal()) {
      eSym->setBindingAndType(STB_LOCAL, sym->type);
    } else {
      eSym->setBindingAndType(sym->computeBinding(), sym->type);
      eSym->setVisibility(sym->visibility);
    }

    // The 3 most significant bits of st_other are used by OpenPOWER ABI.
    // See getPPC64GlobalEntryToLocalEntryOffset() for more details.
    if (config->emachine == EM_PPC64)
      eSym->st_other |= sym->stOther & 0xe0;

    eSym->st_name = ent.strTabOffset;
    if (isDefinedHere)
      eSym->st_shndx = getSymSectionIndex(ent.sym);
    else
      eSym->st_shndx = 0;

    // Copy symbol size if it is a defined symbol. st_size is not significant
    // for undefined symbols, so whether copying it or not is up to us if that's
    // the case. We'll leave it as zero because by not setting a value, we can
    // get the exact same outputs for two sets of input files that differ only
    // in undefined symbol size in DSOs.
    if (eSym->st_shndx == SHN_UNDEF || !isDefinedHere)
      eSym->st_size = 0;
    else
      eSym->st_size = sym->getSize();

    // st_value is usually an address of a symbol, but that has a
    // special meaining for uninstantiated common symbols (this can
    // occur if -r is given).
    if (BssSection *commonSec = getCommonSec(ent.sym))
      eSym->st_value = commonSec->alignment;
    else if (isDefinedHere)
      eSym->st_value = sym->getVA();
    else
      eSym->st_value = 0;

    ++eSym;
  }

  // On MIPS we need to mark symbol which has a PLT entry and requires
  // pointer equality by STO_MIPS_PLT flag. That is necessary to help
  // dynamic linker distinguish such symbols and MIPS lazy-binding stubs.
  // https://sourceware.org/ml/binutils/2008-07/txt00000.txt
  if (config->emachine == EM_MIPS) {
    auto *eSym = reinterpret_cast<Elf_Sym *>(buf);

    for (SymbolTableEntry &ent : symbols) {
      Symbol *sym = ent.sym;
      if (sym->isInPlt() && sym->needsPltAddr)
        eSym->st_other |= STO_MIPS_PLT;
      if (isMicroMips()) {
        // We already set the less-significant bit for symbols
        // marked by the `STO_MIPS_MICROMIPS` flag and for microMIPS PLT
        // records. That allows us to distinguish such symbols in
        // the `MIPS<ELFT>::relocateOne()` routine. Now we should
        // clear that bit for non-dynamic symbol table, so tools
        // like `objdump` will be able to deal with a correct
        // symbol position.
        if (sym->isDefined() &&
            ((sym->stOther & STO_MIPS_MICROMIPS) || sym->needsPltAddr)) {
          if (!strTabSec.isDynamic())
            eSym->st_value &= ~1;
          eSym->st_other |= STO_MIPS_MICROMIPS;
        }
      }
      if (config->relocatable)
        if (auto *d = dyn_cast<Defined>(sym))
          if (isMipsPIC<ELFT>(d))
            eSym->st_other |= STO_MIPS_PIC;
      ++eSym;
    }
  }
}

SymtabShndxSection::SymtabShndxSection()
    : SyntheticSection(0, SHT_SYMTAB_SHNDX, 4, ".symtab_shndx") {
  this->entsize = 4;
}

void SymtabShndxSection::writeTo(uint8_t *buf) {
  // We write an array of 32 bit values, where each value has 1:1 association
  // with an entry in .symtab. If the corresponding entry contains SHN_XINDEX,
  // we need to write actual index, otherwise, we must write SHN_UNDEF(0).
  buf += 4; // Ignore .symtab[0] entry.
  for (const SymbolTableEntry &entry : in.symTab->getSymbols()) {
    if (getSymSectionIndex(entry.sym) == SHN_XINDEX)
      write32(buf, entry.sym->getOutputSection()->sectionIndex);
    buf += 4;
  }
}

bool SymtabShndxSection::isNeeded() const {
  // SHT_SYMTAB can hold symbols with section indices values up to
  // SHN_LORESERVE. If we need more, we want to use extension SHT_SYMTAB_SHNDX
  // section. Problem is that we reveal the final section indices a bit too
  // late, and we do not know them here. For simplicity, we just always create
  // a .symtab_shndx section when the amount of output sections is huge.
  size_t size = 0;
  for (BaseCommand *base : script->sectionCommands)
    if (isa<OutputSection>(base))
      ++size;
  return size >= SHN_LORESERVE;
}

void SymtabShndxSection::finalizeContents() {
  getParent()->link = in.symTab->getParent()->sectionIndex;
}

size_t SymtabShndxSection::getSize() const {
  return in.symTab->getNumSymbols() * 4;
}

// .hash and .gnu.hash sections contain on-disk hash tables that map
// symbol names to their dynamic symbol table indices. Their purpose
// is to help the dynamic linker resolve symbols quickly. If ELF files
// don't have them, the dynamic linker has to do linear search on all
// dynamic symbols, which makes programs slower. Therefore, a .hash
// section is added to a DSO by default. A .gnu.hash is added if you
// give the -hash-style=gnu or -hash-style=both option.
//
// The Unix semantics of resolving dynamic symbols is somewhat expensive.
// Each ELF file has a list of DSOs that the ELF file depends on and a
// list of dynamic symbols that need to be resolved from any of the
// DSOs. That means resolving all dynamic symbols takes O(m)*O(n)
// where m is the number of DSOs and n is the number of dynamic
// symbols. For modern large programs, both m and n are large.  So
// making each step faster by using hash tables substiantially
// improves time to load programs.
//
// (Note that this is not the only way to design the shared library.
// For instance, the Windows DLL takes a different approach. On
// Windows, each dynamic symbol has a name of DLL from which the symbol
// has to be resolved. That makes the cost of symbol resolution O(n).
// This disables some hacky techniques you can use on Unix such as
// LD_PRELOAD, but this is arguably better semantics than the Unix ones.)
//
// Due to historical reasons, we have two different hash tables, .hash
// and .gnu.hash. They are for the same purpose, and .gnu.hash is a new
// and better version of .hash. .hash is just an on-disk hash table, but
// .gnu.hash has a bloom filter in addition to a hash table to skip
// DSOs very quickly. If you are sure that your dynamic linker knows
// about .gnu.hash, you want to specify -hash-style=gnu. Otherwise, a
// safe bet is to specify -hash-style=both for backward compatibilty.
GnuHashTableSection::GnuHashTableSection()
    : SyntheticSection(SHF_ALLOC, SHT_GNU_HASH, config->wordsize, ".gnu.hash") {
}

void GnuHashTableSection::finalizeContents() {
  if (OutputSection *sec = getPartition().dynSymTab->getParent())
    getParent()->link = sec->sectionIndex;

  // Computes bloom filter size in word size. We want to allocate 12
  // bits for each symbol. It must be a power of two.
  if (symbols.empty()) {
    maskWords = 1;
  } else {
    uint64_t numBits = symbols.size() * 12;
    maskWords = NextPowerOf2(numBits / (config->wordsize * 8));
  }

  size = 16;                            // Header
  size += config->wordsize * maskWords; // Bloom filter
  size += nBuckets * 4;                 // Hash buckets
  size += symbols.size() * 4;           // Hash values
}

void GnuHashTableSection::writeTo(uint8_t *buf) {
  // The output buffer is not guaranteed to be zero-cleared because we pre-
  // fill executable sections with trap instructions. This is a precaution
  // for that case, which happens only when -no-rosegment is given.
  memset(buf, 0, size);

  // Write a header.
  write32(buf, nBuckets);
  write32(buf + 4, getPartition().dynSymTab->getNumSymbols() - symbols.size());
  write32(buf + 8, maskWords);
  write32(buf + 12, Shift2);
  buf += 16;

  // Write a bloom filter and a hash table.
  writeBloomFilter(buf);
  buf += config->wordsize * maskWords;
  writeHashTable(buf);
}

// This function writes a 2-bit bloom filter. This bloom filter alone
// usually filters out 80% or more of all symbol lookups [1].
// The dynamic linker uses the hash table only when a symbol is not
// filtered out by a bloom filter.
//
// [1] Ulrich Drepper (2011), "How To Write Shared Libraries" (Ver. 4.1.2),
//     p.9, https://www.akkadia.org/drepper/dsohowto.pdf
void GnuHashTableSection::writeBloomFilter(uint8_t *buf) {
  unsigned c = config->is64 ? 64 : 32;
  for (const Entry &sym : symbols) {
    // When C = 64, we choose a word with bits [6:...] and set 1 to two bits in
    // the word using bits [0:5] and [26:31].
    size_t i = (sym.hash / c) & (maskWords - 1);
    uint64_t val = readUint(buf + i * config->wordsize);
    val |= uint64_t(1) << (sym.hash % c);
    val |= uint64_t(1) << ((sym.hash >> Shift2) % c);
    writeUint(buf + i * config->wordsize, val);
  }
}

void GnuHashTableSection::writeHashTable(uint8_t *buf) {
  uint32_t *buckets = reinterpret_cast<uint32_t *>(buf);
  uint32_t oldBucket = -1;
  uint32_t *values = buckets + nBuckets;
  for (auto i = symbols.begin(), e = symbols.end(); i != e; ++i) {
    // Write a hash value. It represents a sequence of chains that share the
    // same hash modulo value. The last element of each chain is terminated by
    // LSB 1.
    uint32_t hash = i->hash;
    bool isLastInChain = (i + 1) == e || i->bucketIdx != (i + 1)->bucketIdx;
    hash = isLastInChain ? hash | 1 : hash & ~1;
    write32(values++, hash);

    if (i->bucketIdx == oldBucket)
      continue;
    // Write a hash bucket. Hash buckets contain indices in the following hash
    // value table.
    write32(buckets + i->bucketIdx,
            getPartition().dynSymTab->getSymbolIndex(i->sym));
    oldBucket = i->bucketIdx;
  }
}

static uint32_t hashGnu(StringRef name) {
  uint32_t h = 5381;
  for (uint8_t c : name)
    h = (h << 5) + h + c;
  return h;
}

// Add symbols to this symbol hash table. Note that this function
// destructively sort a given vector -- which is needed because
// GNU-style hash table places some sorting requirements.
void GnuHashTableSection::addSymbols(std::vector<SymbolTableEntry> &v) {
  // We cannot use 'auto' for Mid because GCC 6.1 cannot deduce
  // its type correctly.
  std::vector<SymbolTableEntry>::iterator mid =
      std::stable_partition(v.begin(), v.end(), [&](const SymbolTableEntry &s) {
        return !s.sym->isDefined() || s.sym->partition != partition;
      });

  // We chose load factor 4 for the on-disk hash table. For each hash
  // collision, the dynamic linker will compare a uint32_t hash value.
  // Since the integer comparison is quite fast, we believe we can
  // make the load factor even larger. 4 is just a conservative choice.
  //
  // Note that we don't want to create a zero-sized hash table because
  // Android loader as of 2018 doesn't like a .gnu.hash containing such
  // table. If that's the case, we create a hash table with one unused
  // dummy slot.
  nBuckets = std::max<size_t>((v.end() - mid) / 4, 1);

  if (mid == v.end())
    return;

  for (SymbolTableEntry &ent : llvm::make_range(mid, v.end())) {
    Symbol *b = ent.sym;
    uint32_t hash = hashGnu(b->getName());
    uint32_t bucketIdx = hash % nBuckets;
    symbols.push_back({b, ent.strTabOffset, hash, bucketIdx});
  }

  llvm::stable_sort(symbols, [](const Entry &l, const Entry &r) {
    return l.bucketIdx < r.bucketIdx;
  });

  v.erase(mid, v.end());
  for (const Entry &ent : symbols)
    v.push_back({ent.sym, ent.strTabOffset});
}

HashTableSection::HashTableSection()
    : SyntheticSection(SHF_ALLOC, SHT_HASH, 4, ".hash") {
  this->entsize = 4;
}

void HashTableSection::finalizeContents() {
  SymbolTableBaseSection *symTab = getPartition().dynSymTab;

  if (OutputSection *sec = symTab->getParent())
    getParent()->link = sec->sectionIndex;

  unsigned numEntries = 2;               // nbucket and nchain.
  numEntries += symTab->getNumSymbols(); // The chain entries.

  // Create as many buckets as there are symbols.
  numEntries += symTab->getNumSymbols();
  this->size = numEntries * 4;
}

void HashTableSection::writeTo(uint8_t *buf) {
  SymbolTableBaseSection *symTab = getPartition().dynSymTab;

  // See comment in GnuHashTableSection::writeTo.
  memset(buf, 0, size);

  unsigned numSymbols = symTab->getNumSymbols();

  uint32_t *p = reinterpret_cast<uint32_t *>(buf);
  write32(p++, numSymbols); // nbucket
  write32(p++, numSymbols); // nchain

  uint32_t *buckets = p;
  uint32_t *chains = p + numSymbols;

  for (const SymbolTableEntry &s : symTab->getSymbols()) {
    Symbol *sym = s.sym;
    StringRef name = sym->getName();
    unsigned i = sym->dynsymIndex;
    uint32_t hash = hashSysV(name) % numSymbols;
    chains[i] = buckets[hash];
    write32(buckets + hash, i);
  }
}

// On PowerPC64 the lazy symbol resolvers go into the `global linkage table`
// in the .glink section, rather then the typical .plt section.
PltSection::PltSection(bool isIplt)
    : SyntheticSection(
          SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS, 16,
          (config->emachine == EM_PPC || config->emachine == EM_PPC64)
              ? ".glink"
              : ".plt"),
      headerSize(!isIplt || config->zRetpolineplt ? target->pltHeaderSize : 0),
      isIplt(isIplt) {
  // The PLT needs to be writable on SPARC as the dynamic linker will
  // modify the instructions in the PLT entries.
  if (config->emachine == EM_SPARCV9)
    this->flags |= SHF_WRITE;
}

void PltSection::writeTo(uint8_t *buf) {
  if (config->emachine == EM_PPC) {
    writePPC32GlinkSection(buf, entries.size());
    return;
  }

  // At beginning of PLT or retpoline IPLT, we have code to call the dynamic
  // linker to resolve dynsyms at runtime. Write such code.
  if (headerSize)
    target->writePltHeader(buf);
  size_t off = headerSize;

  RelocationBaseSection *relSec = isIplt ? in.relaIplt : in.relaPlt;

  // The IPlt is immediately after the Plt, account for this in relOff
  size_t pltOff = isIplt ? in.plt->getSize() : 0;

  for (size_t i = 0, e = entries.size(); i != e; ++i) {
    const Symbol *b = entries[i];
    unsigned relOff = relSec->entsize * i + pltOff;
    uint64_t got = b->getGotPltVA();
    uint64_t plt = this->getVA() + off;
    target->writePlt(buf + off, got, plt, b->pltIndex, relOff);
    off += target->pltEntrySize;
  }
}

template <class ELFT> void PltSection::addEntry(Symbol &sym) {
  sym.pltIndex = entries.size();
  entries.push_back(&sym);
}

size_t PltSection::getSize() const {
  return headerSize + entries.size() * target->pltEntrySize;
}

// Some architectures such as additional symbols in the PLT section. For
// example ARM uses mapping symbols to aid disassembly
void PltSection::addSymbols() {
  // The PLT may have symbols defined for the Header, the IPLT has no header
  if (!isIplt)
    target->addPltHeaderSymbols(*this);

  size_t off = headerSize;
  for (size_t i = 0; i < entries.size(); ++i) {
    target->addPltSymbols(*this, off);
    off += target->pltEntrySize;
  }
}

// The string hash function for .gdb_index.
static uint32_t computeGdbHash(StringRef s) {
  uint32_t h = 0;
  for (uint8_t c : s)
    h = h * 67 + toLower(c) - 113;
  return h;
}

GdbIndexSection::GdbIndexSection()
    : SyntheticSection(0, SHT_PROGBITS, 1, ".gdb_index") {}

// Returns the desired size of an on-disk hash table for a .gdb_index section.
// There's a tradeoff between size and collision rate. We aim 75% utilization.
size_t GdbIndexSection::computeSymtabSize() const {
  return std::max<size_t>(NextPowerOf2(symbols.size() * 4 / 3), 1024);
}

// Compute the output section size.
void GdbIndexSection::initOutputSize() {
  size = sizeof(GdbIndexHeader) + computeSymtabSize() * 8;

  for (GdbChunk &chunk : chunks)
    size += chunk.compilationUnits.size() * 16 + chunk.addressAreas.size() * 20;

  // Add the constant pool size if exists.
  if (!symbols.empty()) {
    GdbSymbol &sym = symbols.back();
    size += sym.nameOff + sym.name.size() + 1;
  }
}

static std::vector<InputSection *> getDebugInfoSections() {
  std::vector<InputSection *> ret;
  for (InputSectionBase *s : inputSections)
    if (InputSection *isec = dyn_cast<InputSection>(s))
      if (isec->name == ".debug_info")
        ret.push_back(isec);
  return ret;
}

static std::vector<GdbIndexSection::CuEntry> readCuList(DWARFContext &dwarf) {
  std::vector<GdbIndexSection::CuEntry> ret;
  for (std::unique_ptr<DWARFUnit> &cu : dwarf.compile_units())
    ret.push_back({cu->getOffset(), cu->getLength() + 4});
  return ret;
}

static std::vector<GdbIndexSection::AddressEntry>
readAddressAreas(DWARFContext &dwarf, InputSection *sec) {
  std::vector<GdbIndexSection::AddressEntry> ret;

  uint32_t cuIdx = 0;
  for (std::unique_ptr<DWARFUnit> &cu : dwarf.compile_units()) {
    Expected<DWARFAddressRangesVector> ranges = cu->collectAddressRanges();
    if (!ranges) {
      error(toString(sec) + ": " + toString(ranges.takeError()));
      return {};
    }

    ArrayRef<InputSectionBase *> sections = sec->file->getSections();
    for (DWARFAddressRange &r : *ranges) {
      if (r.SectionIndex == -1ULL)
        continue;
      InputSectionBase *s = sections[r.SectionIndex];
      if (!s || s == &InputSection::discarded || !s->isLive())
        continue;
      // Range list with zero size has no effect.
      if (r.LowPC == r.HighPC)
        continue;
      auto *isec = cast<InputSection>(s);
      uint64_t offset = isec->getOffsetInFile();
      ret.push_back({isec, r.LowPC - offset, r.HighPC - offset, cuIdx});
    }
    ++cuIdx;
  }

  return ret;
}

template <class ELFT>
static std::vector<GdbIndexSection::NameAttrEntry>
readPubNamesAndTypes(const LLDDwarfObj<ELFT> &obj,
                     const std::vector<GdbIndexSection::CuEntry> &cUs) {
  const DWARFSection &pubNames = obj.getGnuPubNamesSection();
  const DWARFSection &pubTypes = obj.getGnuPubTypesSection();

  std::vector<GdbIndexSection::NameAttrEntry> ret;
  for (const DWARFSection *pub : {&pubNames, &pubTypes}) {
    DWARFDebugPubTable table(obj, *pub, config->isLE, true);
    for (const DWARFDebugPubTable::Set &set : table.getData()) {
      // The value written into the constant pool is kind << 24 | cuIndex. As we
      // don't know how many compilation units precede this object to compute
      // cuIndex, we compute (kind << 24 | cuIndexInThisObject) instead, and add
      // the number of preceding compilation units later.
      uint32_t i =
          lower_bound(cUs, set.Offset,
                      [](GdbIndexSection::CuEntry cu, uint32_t offset) {
                        return cu.cuOffset < offset;
                      }) -
          cUs.begin();
      for (const DWARFDebugPubTable::Entry &ent : set.Entries)
        ret.push_back({{ent.Name, computeGdbHash(ent.Name)},
                       (ent.Descriptor.toBits() << 24) | i});
    }
  }
  return ret;
}

// Create a list of symbols from a given list of symbol names and types
// by uniquifying them by name.
static std::vector<GdbIndexSection::GdbSymbol>
createSymbols(ArrayRef<std::vector<GdbIndexSection::NameAttrEntry>> nameAttrs,
              const std::vector<GdbIndexSection::GdbChunk> &chunks) {
  using GdbSymbol = GdbIndexSection::GdbSymbol;
  using NameAttrEntry = GdbIndexSection::NameAttrEntry;

  // For each chunk, compute the number of compilation units preceding it.
  uint32_t cuIdx = 0;
  std::vector<uint32_t> cuIdxs(chunks.size());
  for (uint32_t i = 0, e = chunks.size(); i != e; ++i) {
    cuIdxs[i] = cuIdx;
    cuIdx += chunks[i].compilationUnits.size();
  }

  // The number of symbols we will handle in this function is of the order
  // of millions for very large executables, so we use multi-threading to
  // speed it up.
  size_t numShards = 32;
  size_t concurrency = 1;
  if (threadsEnabled)
    concurrency =
        std::min<size_t>(PowerOf2Floor(hardware_concurrency()), numShards);

  // A sharded map to uniquify symbols by name.
  std::vector<DenseMap<CachedHashStringRef, size_t>> map(numShards);
  size_t shift = 32 - countTrailingZeros(numShards);

  // Instantiate GdbSymbols while uniqufying them by name.
  std::vector<std::vector<GdbSymbol>> symbols(numShards);
  parallelForEachN(0, concurrency, [&](size_t threadId) {
    uint32_t i = 0;
    for (ArrayRef<NameAttrEntry> entries : nameAttrs) {
      for (const NameAttrEntry &ent : entries) {
        size_t shardId = ent.name.hash() >> shift;
        if ((shardId & (concurrency - 1)) != threadId)
          continue;

        uint32_t v = ent.cuIndexAndAttrs + cuIdxs[i];
        size_t &idx = map[shardId][ent.name];
        if (idx) {
          symbols[shardId][idx - 1].cuVector.push_back(v);
          continue;
        }

        idx = symbols[shardId].size() + 1;
        symbols[shardId].push_back({ent.name, {v}, 0, 0});
      }
      ++i;
    }
  });

  size_t numSymbols = 0;
  for (ArrayRef<GdbSymbol> v : symbols)
    numSymbols += v.size();

  // The return type is a flattened vector, so we'll copy each vector
  // contents to Ret.
  std::vector<GdbSymbol> ret;
  ret.reserve(numSymbols);
  for (std::vector<GdbSymbol> &vec : symbols)
    for (GdbSymbol &sym : vec)
      ret.push_back(std::move(sym));

  // CU vectors and symbol names are adjacent in the output file.
  // We can compute their offsets in the output file now.
  size_t off = 0;
  for (GdbSymbol &sym : ret) {
    sym.cuVectorOff = off;
    off += (sym.cuVector.size() + 1) * 4;
  }
  for (GdbSymbol &sym : ret) {
    sym.nameOff = off;
    off += sym.name.size() + 1;
  }

  return ret;
}

// Returns a newly-created .gdb_index section.
template <class ELFT> GdbIndexSection *GdbIndexSection::create() {
  std::vector<InputSection *> sections = getDebugInfoSections();

  // .debug_gnu_pub{names,types} are useless in executables.
  // They are present in input object files solely for creating
  // a .gdb_index. So we can remove them from the output.
  for (InputSectionBase *s : inputSections)
    if (s->name == ".debug_gnu_pubnames" || s->name == ".debug_gnu_pubtypes")
      s->markDead();

  std::vector<GdbChunk> chunks(sections.size());
  std::vector<std::vector<NameAttrEntry>> nameAttrs(sections.size());

  parallelForEachN(0, sections.size(), [&](size_t i) {
    ObjFile<ELFT> *file = sections[i]->getFile<ELFT>();
    DWARFContext dwarf(make_unique<LLDDwarfObj<ELFT>>(file));

    chunks[i].sec = sections[i];
    chunks[i].compilationUnits = readCuList(dwarf);
    chunks[i].addressAreas = readAddressAreas(dwarf, sections[i]);
    nameAttrs[i] = readPubNamesAndTypes<ELFT>(
        static_cast<const LLDDwarfObj<ELFT> &>(dwarf.getDWARFObj()),
        chunks[i].compilationUnits);
  });

  auto *ret = make<GdbIndexSection>();
  ret->chunks = std::move(chunks);
  ret->symbols = createSymbols(nameAttrs, ret->chunks);
  ret->initOutputSize();
  return ret;
}

void GdbIndexSection::writeTo(uint8_t *buf) {
  // Write the header.
  auto *hdr = reinterpret_cast<GdbIndexHeader *>(buf);
  uint8_t *start = buf;
  hdr->version = 7;
  buf += sizeof(*hdr);

  // Write the CU list.
  hdr->cuListOff = buf - start;
  for (GdbChunk &chunk : chunks) {
    for (CuEntry &cu : chunk.compilationUnits) {
      write64le(buf, chunk.sec->outSecOff + cu.cuOffset);
      write64le(buf + 8, cu.cuLength);
      buf += 16;
    }
  }

  // Write the address area.
  hdr->cuTypesOff = buf - start;
  hdr->addressAreaOff = buf - start;
  uint32_t cuOff = 0;
  for (GdbChunk &chunk : chunks) {
    for (AddressEntry &e : chunk.addressAreas) {
      uint64_t baseAddr = e.section->getVA(0);
      write64le(buf, baseAddr + e.lowAddress);
      write64le(buf + 8, baseAddr + e.highAddress);
      write32le(buf + 16, e.cuIndex + cuOff);
      buf += 20;
    }
    cuOff += chunk.compilationUnits.size();
  }

  // Write the on-disk open-addressing hash table containing symbols.
  hdr->symtabOff = buf - start;
  size_t symtabSize = computeSymtabSize();
  uint32_t mask = symtabSize - 1;

  for (GdbSymbol &sym : symbols) {
    uint32_t h = sym.name.hash();
    uint32_t i = h & mask;
    uint32_t step = ((h * 17) & mask) | 1;

    while (read32le(buf + i * 8))
      i = (i + step) & mask;

    write32le(buf + i * 8, sym.nameOff);
    write32le(buf + i * 8 + 4, sym.cuVectorOff);
  }

  buf += symtabSize * 8;

  // Write the string pool.
  hdr->constantPoolOff = buf - start;
  parallelForEach(symbols, [&](GdbSymbol &sym) {
    memcpy(buf + sym.nameOff, sym.name.data(), sym.name.size());
  });

  // Write the CU vectors.
  for (GdbSymbol &sym : symbols) {
    write32le(buf, sym.cuVector.size());
    buf += 4;
    for (uint32_t val : sym.cuVector) {
      write32le(buf, val);
      buf += 4;
    }
  }
}

bool GdbIndexSection::isNeeded() const { return !chunks.empty(); }

EhFrameHeader::EhFrameHeader()
    : SyntheticSection(SHF_ALLOC, SHT_PROGBITS, 4, ".eh_frame_hdr") {}

void EhFrameHeader::writeTo(uint8_t *buf) {
  // Unlike most sections, the EhFrameHeader section is written while writing
  // another section, namely EhFrameSection, which calls the write() function
  // below from its writeTo() function. This is necessary because the contents
  // of EhFrameHeader depend on the relocated contents of EhFrameSection and we
  // don't know which order the sections will be written in.
}

// .eh_frame_hdr contains a binary search table of pointers to FDEs.
// Each entry of the search table consists of two values,
// the starting PC from where FDEs covers, and the FDE's address.
// It is sorted by PC.
void EhFrameHeader::write() {
  uint8_t *buf = Out::bufferStart + getParent()->offset + outSecOff;
  using FdeData = EhFrameSection::FdeData;

  std::vector<FdeData> fdes = getPartition().ehFrame->getFdeData();

  buf[0] = 1;
  buf[1] = DW_EH_PE_pcrel | DW_EH_PE_sdata4;
  buf[2] = DW_EH_PE_udata4;
  buf[3] = DW_EH_PE_datarel | DW_EH_PE_sdata4;
  write32(buf + 4,
          getPartition().ehFrame->getParent()->addr - this->getVA() - 4);
  write32(buf + 8, fdes.size());
  buf += 12;

  for (FdeData &fde : fdes) {
    write32(buf, fde.pcRel);
    write32(buf + 4, fde.fdeVARel);
    buf += 8;
  }
}

size_t EhFrameHeader::getSize() const {
  // .eh_frame_hdr has a 12 bytes header followed by an array of FDEs.
  return 12 + getPartition().ehFrame->numFdes * 8;
}

bool EhFrameHeader::isNeeded() const {
  return isLive() && getPartition().ehFrame->isNeeded();
}

VersionDefinitionSection::VersionDefinitionSection()
    : SyntheticSection(SHF_ALLOC, SHT_GNU_verdef, sizeof(uint32_t),
                       ".gnu.version_d") {}

StringRef VersionDefinitionSection::getFileDefName() {
  if (!getPartition().name.empty())
    return getPartition().name;
  if (!config->soName.empty())
    return config->soName;
  return config->outputFile;
}

void VersionDefinitionSection::finalizeContents() {
  fileDefNameOff = getPartition().dynStrTab->addString(getFileDefName());
  for (VersionDefinition &v : config->versionDefinitions)
    verDefNameOffs.push_back(getPartition().dynStrTab->addString(v.name));

  if (OutputSection *sec = getPartition().dynStrTab->getParent())
    getParent()->link = sec->sectionIndex;

  // sh_info should be set to the number of definitions. This fact is missed in
  // documentation, but confirmed by binutils community:
  // https://sourceware.org/ml/binutils/2014-11/msg00355.html
  getParent()->info = getVerDefNum();
}

void VersionDefinitionSection::writeOne(uint8_t *buf, uint32_t index,
                                        StringRef name, size_t nameOff) {
  uint16_t flags = index == 1 ? VER_FLG_BASE : 0;

  // Write a verdef.
  write16(buf, 1);                  // vd_version
  write16(buf + 2, flags);          // vd_flags
  write16(buf + 4, index);          // vd_ndx
  write16(buf + 6, 1);              // vd_cnt
  write32(buf + 8, hashSysV(name)); // vd_hash
  write32(buf + 12, 20);            // vd_aux
  write32(buf + 16, 28);            // vd_next

  // Write a veraux.
  write32(buf + 20, nameOff); // vda_name
  write32(buf + 24, 0);       // vda_next
}

void VersionDefinitionSection::writeTo(uint8_t *buf) {
  writeOne(buf, 1, getFileDefName(), fileDefNameOff);

  auto nameOffIt = verDefNameOffs.begin();
  for (VersionDefinition &v : config->versionDefinitions) {
    buf += EntrySize;
    writeOne(buf, v.id, v.name, *nameOffIt++);
  }

  // Need to terminate the last version definition.
  write32(buf + 16, 0); // vd_next
}

size_t VersionDefinitionSection::getSize() const {
  return EntrySize * getVerDefNum();
}

// .gnu.version is a table where each entry is 2 byte long.
VersionTableSection::VersionTableSection()
    : SyntheticSection(SHF_ALLOC, SHT_GNU_versym, sizeof(uint16_t),
                       ".gnu.version") {
  this->entsize = 2;
}

void VersionTableSection::finalizeContents() {
  // At the moment of june 2016 GNU docs does not mention that sh_link field
  // should be set, but Sun docs do. Also readelf relies on this field.
  getParent()->link = getPartition().dynSymTab->getParent()->sectionIndex;
}

size_t VersionTableSection::getSize() const {
  return (getPartition().dynSymTab->getSymbols().size() + 1) * 2;
}

void VersionTableSection::writeTo(uint8_t *buf) {
  buf += 2;
  for (const SymbolTableEntry &s : getPartition().dynSymTab->getSymbols()) {
    write16(buf, s.sym->versionId);
    buf += 2;
  }
}

bool VersionTableSection::isNeeded() const {
  return getPartition().verDef || getPartition().verNeed->isNeeded();
}

void elf::addVerneed(Symbol *ss) {
  auto &file = cast<SharedFile>(*ss->file);
  if (ss->verdefIndex == VER_NDX_GLOBAL) {
    ss->versionId = VER_NDX_GLOBAL;
    return;
  }

  if (file.vernauxs.empty())
    file.vernauxs.resize(file.verdefs.size());

  // Select a version identifier for the vernaux data structure, if we haven't
  // already allocated one. The verdef identifiers cover the range
  // [1..getVerDefNum()]; this causes the vernaux identifiers to start from
  // getVerDefNum()+1.
  if (file.vernauxs[ss->verdefIndex] == 0)
    file.vernauxs[ss->verdefIndex] = ++SharedFile::vernauxNum + getVerDefNum();

  ss->versionId = file.vernauxs[ss->verdefIndex];
}

template <class ELFT>
VersionNeedSection<ELFT>::VersionNeedSection()
    : SyntheticSection(SHF_ALLOC, SHT_GNU_verneed, sizeof(uint32_t),
                       ".gnu.version_r") {}

template <class ELFT> void VersionNeedSection<ELFT>::finalizeContents() {
  for (SharedFile *f : sharedFiles) {
    if (f->vernauxs.empty())
      continue;
    verneeds.emplace_back();
    Verneed &vn = verneeds.back();
    vn.nameStrTab = getPartition().dynStrTab->addString(f->soName);
    for (unsigned i = 0; i != f->vernauxs.size(); ++i) {
      if (f->vernauxs[i] == 0)
        continue;
      auto *verdef =
          reinterpret_cast<const typename ELFT::Verdef *>(f->verdefs[i]);
      vn.vernauxs.push_back(
          {verdef->vd_hash, f->vernauxs[i],
           getPartition().dynStrTab->addString(f->getStringTable().data() +
                                               verdef->getAux()->vda_name)});
    }
  }

  if (OutputSection *sec = getPartition().dynStrTab->getParent())
    getParent()->link = sec->sectionIndex;
  getParent()->info = verneeds.size();
}

template <class ELFT> void VersionNeedSection<ELFT>::writeTo(uint8_t *buf) {
  // The Elf_Verneeds need to appear first, followed by the Elf_Vernauxs.
  auto *verneed = reinterpret_cast<Elf_Verneed *>(buf);
  auto *vernaux = reinterpret_cast<Elf_Vernaux *>(verneed + verneeds.size());

  for (auto &vn : verneeds) {
    // Create an Elf_Verneed for this DSO.
    verneed->vn_version = 1;
    verneed->vn_cnt = vn.vernauxs.size();
    verneed->vn_file = vn.nameStrTab;
    verneed->vn_aux =
        reinterpret_cast<char *>(vernaux) - reinterpret_cast<char *>(verneed);
    verneed->vn_next = sizeof(Elf_Verneed);
    ++verneed;

    // Create the Elf_Vernauxs for this Elf_Verneed.
    for (auto &vna : vn.vernauxs) {
      vernaux->vna_hash = vna.hash;
      vernaux->vna_flags = 0;
      vernaux->vna_other = vna.verneedIndex;
      vernaux->vna_name = vna.nameStrTab;
      vernaux->vna_next = sizeof(Elf_Vernaux);
      ++vernaux;
    }

    vernaux[-1].vna_next = 0;
  }
  verneed[-1].vn_next = 0;
}

template <class ELFT> size_t VersionNeedSection<ELFT>::getSize() const {
  return verneeds.size() * sizeof(Elf_Verneed) +
         SharedFile::vernauxNum * sizeof(Elf_Vernaux);
}

template <class ELFT> bool VersionNeedSection<ELFT>::isNeeded() const {
  return SharedFile::vernauxNum != 0;
}

void MergeSyntheticSection::addSection(MergeInputSection *ms) {
  ms->parent = this;
  sections.push_back(ms);
  assert(alignment == ms->alignment || !(ms->flags & SHF_STRINGS));
  alignment = std::max(alignment, ms->alignment);
}

MergeTailSection::MergeTailSection(StringRef name, uint32_t type,
                                   uint64_t flags, uint32_t alignment)
    : MergeSyntheticSection(name, type, flags, alignment),
      builder(StringTableBuilder::RAW, alignment) {}

size_t MergeTailSection::getSize() const { return builder.getSize(); }

void MergeTailSection::writeTo(uint8_t *buf) { builder.write(buf); }

void MergeTailSection::finalizeContents() {
  // Add all string pieces to the string table builder to create section
  // contents.
  for (MergeInputSection *sec : sections)
    for (size_t i = 0, e = sec->pieces.size(); i != e; ++i)
      if (sec->pieces[i].live)
        builder.add(sec->getData(i));

  // Fix the string table content. After this, the contents will never change.
  builder.finalize();

  // finalize() fixed tail-optimized strings, so we can now get
  // offsets of strings. Get an offset for each string and save it
  // to a corresponding SectionPiece for easy access.
  for (MergeInputSection *sec : sections)
    for (size_t i = 0, e = sec->pieces.size(); i != e; ++i)
      if (sec->pieces[i].live)
        sec->pieces[i].outputOff = builder.getOffset(sec->getData(i));
}

void MergeNoTailSection::writeTo(uint8_t *buf) {
  for (size_t i = 0; i < numShards; ++i)
    shards[i].write(buf + shardOffsets[i]);
}

// This function is very hot (i.e. it can take several seconds to finish)
// because sometimes the number of inputs is in an order of magnitude of
// millions. So, we use multi-threading.
//
// For any strings S and T, we know S is not mergeable with T if S's hash
// value is different from T's. If that's the case, we can safely put S and
// T into different string builders without worrying about merge misses.
// We do it in parallel.
void MergeNoTailSection::finalizeContents() {
  // Initializes string table builders.
  for (size_t i = 0; i < numShards; ++i)
    shards.emplace_back(StringTableBuilder::RAW, alignment);

  // Concurrency level. Must be a power of 2 to avoid expensive modulo
  // operations in the following tight loop.
  size_t concurrency = 1;
  if (threadsEnabled)
    concurrency =
        std::min<size_t>(PowerOf2Floor(hardware_concurrency()), numShards);

  // Add section pieces to the builders.
  parallelForEachN(0, concurrency, [&](size_t threadId) {
    for (MergeInputSection *sec : sections) {
      for (size_t i = 0, e = sec->pieces.size(); i != e; ++i) {
        if (!sec->pieces[i].live)
          continue;
        size_t shardId = getShardId(sec->pieces[i].hash);
        if ((shardId & (concurrency - 1)) == threadId)
          sec->pieces[i].outputOff = shards[shardId].add(sec->getData(i));
      }
    }
  });

  // Compute an in-section offset for each shard.
  size_t off = 0;
  for (size_t i = 0; i < numShards; ++i) {
    shards[i].finalizeInOrder();
    if (shards[i].getSize() > 0)
      off = alignTo(off, alignment);
    shardOffsets[i] = off;
    off += shards[i].getSize();
  }
  size = off;

  // So far, section pieces have offsets from beginning of shards, but
  // we want offsets from beginning of the whole section. Fix them.
  parallelForEach(sections, [&](MergeInputSection *sec) {
    for (size_t i = 0, e = sec->pieces.size(); i != e; ++i)
      if (sec->pieces[i].live)
        sec->pieces[i].outputOff +=
            shardOffsets[getShardId(sec->pieces[i].hash)];
  });
}

static MergeSyntheticSection *createMergeSynthetic(StringRef name,
                                                   uint32_t type,
                                                   uint64_t flags,
                                                   uint32_t alignment) {
  bool shouldTailMerge = (flags & SHF_STRINGS) && config->optimize >= 2;
  if (shouldTailMerge)
    return make<MergeTailSection>(name, type, flags, alignment);
  return make<MergeNoTailSection>(name, type, flags, alignment);
}

template <class ELFT> void elf::splitSections() {
  // splitIntoPieces needs to be called on each MergeInputSection
  // before calling finalizeContents().
  parallelForEach(inputSections, [](InputSectionBase *sec) {
    if (auto *s = dyn_cast<MergeInputSection>(sec))
      s->splitIntoPieces();
    else if (auto *eh = dyn_cast<EhInputSection>(sec))
      eh->split<ELFT>();
  });
}

// This function scans over the inputsections to create mergeable
// synthetic sections.
//
// It removes MergeInputSections from the input section array and adds
// new synthetic sections at the location of the first input section
// that it replaces. It then finalizes each synthetic section in order
// to compute an output offset for each piece of each input section.
void elf::mergeSections() {
  std::vector<MergeSyntheticSection *> mergeSections;
  for (InputSectionBase *&s : inputSections) {
    MergeInputSection *ms = dyn_cast<MergeInputSection>(s);
    if (!ms)
      continue;

    // We do not want to handle sections that are not alive, so just remove
    // them instead of trying to merge.
    if (!ms->isLive()) {
      s = nullptr;
      continue;
    }

    StringRef outsecName = getOutputSectionName(ms);

    auto i = llvm::find_if(mergeSections, [=](MergeSyntheticSection *sec) {
      // While we could create a single synthetic section for two different
      // values of Entsize, it is better to take Entsize into consideration.
      //
      // With a single synthetic section no two pieces with different Entsize
      // could be equal, so we may as well have two sections.
      //
      // Using Entsize in here also allows us to propagate it to the synthetic
      // section.
      //
      // SHF_STRINGS section with different alignments should not be merged.
      return sec->name == outsecName && sec->flags == ms->flags &&
             sec->entsize == ms->entsize &&
             (sec->alignment == ms->alignment || !(sec->flags & SHF_STRINGS));
    });
    if (i == mergeSections.end()) {
      MergeSyntheticSection *syn =
          createMergeSynthetic(outsecName, ms->type, ms->flags, ms->alignment);
      mergeSections.push_back(syn);
      i = std::prev(mergeSections.end());
      s = syn;
      syn->entsize = ms->entsize;
    } else {
      s = nullptr;
    }
    (*i)->addSection(ms);
  }
  for (auto *ms : mergeSections)
    ms->finalizeContents();

  std::vector<InputSectionBase *> &v = inputSections;
  v.erase(std::remove(v.begin(), v.end(), nullptr), v.end());
}

MipsRldMapSection::MipsRldMapSection()
    : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS, config->wordsize,
                       ".rld_map") {}

ARMExidxSyntheticSection::ARMExidxSyntheticSection()
    : SyntheticSection(SHF_ALLOC | SHF_LINK_ORDER, SHT_ARM_EXIDX,
                       config->wordsize, ".ARM.exidx") {}

static InputSection *findExidxSection(InputSection *isec) {
  for (InputSection *d : isec->dependentSections)
    if (d->type == SHT_ARM_EXIDX)
      return d;
  return nullptr;
}

bool ARMExidxSyntheticSection::addSection(InputSection *isec) {
  if (isec->type == SHT_ARM_EXIDX) {
    exidxSections.push_back(isec);
    return true;
  }

  if ((isec->flags & SHF_ALLOC) && (isec->flags & SHF_EXECINSTR) &&
      isec->getSize() > 0) {
    executableSections.push_back(isec);
    if (empty && findExidxSection(isec))
      empty = false;
    return false;
  }

  // FIXME: we do not output a relocation section when --emit-relocs is used
  // as we do not have relocation sections for linker generated table entries
  // and we would have to erase at a late stage relocations from merged entries.
  // Given that exception tables are already position independent and a binary
  // analyzer could derive the relocations we choose to erase the relocations.
  if (config->emitRelocs && isec->type == SHT_REL)
    if (InputSectionBase *ex = isec->getRelocatedSection())
      if (isa<InputSection>(ex) && ex->type == SHT_ARM_EXIDX)
        return true;

  return false;
}

// References to .ARM.Extab Sections have bit 31 clear and are not the
// special EXIDX_CANTUNWIND bit-pattern.
static bool isExtabRef(uint32_t unwind) {
  return (unwind & 0x80000000) == 0 && unwind != 0x1;
}

// Return true if the .ARM.exidx section Cur can be merged into the .ARM.exidx
// section Prev, where Cur follows Prev in the table. This can be done if the
// unwinding instructions in Cur are identical to Prev. Linker generated
// EXIDX_CANTUNWIND entries are represented by nullptr as they do not have an
// InputSection.
static bool isDuplicateArmExidxSec(InputSection *prev, InputSection *cur) {

  struct ExidxEntry {
    ulittle32_t fn;
    ulittle32_t unwind;
  };
  // Get the last table Entry from the previous .ARM.exidx section. If Prev is
  // nullptr then it will be a synthesized EXIDX_CANTUNWIND entry.
  ExidxEntry prevEntry = {ulittle32_t(0), ulittle32_t(1)};
  if (prev)
    prevEntry = prev->getDataAs<ExidxEntry>().back();
  if (isExtabRef(prevEntry.unwind))
    return false;

  // We consider the unwind instructions of an .ARM.exidx table entry
  // a duplicate if the previous unwind instructions if:
  // - Both are the special EXIDX_CANTUNWIND.
  // - Both are the same inline unwind instructions.
  // We do not attempt to follow and check links into .ARM.extab tables as
  // consecutive identical entries are rare and the effort to check that they
  // are identical is high.

  // If Cur is nullptr then this is synthesized EXIDX_CANTUNWIND entry.
  if (cur == nullptr)
    return prevEntry.unwind == 1;

  for (const ExidxEntry entry : cur->getDataAs<ExidxEntry>())
    if (isExtabRef(entry.unwind) || entry.unwind != prevEntry.unwind)
      return false;

  // All table entries in this .ARM.exidx Section can be merged into the
  // previous Section.
  return true;
}

// The .ARM.exidx table must be sorted in ascending order of the address of the
// functions the table describes. Optionally duplicate adjacent table entries
// can be removed. At the end of the function the ExecutableSections must be
// sorted in ascending order of address, Sentinel is set to the InputSection
// with the highest address and any InputSections that have mergeable
// .ARM.exidx table entries are removed from it.
void ARMExidxSyntheticSection::finalizeContents() {
  // Sort the executable sections that may or may not have associated
  // .ARM.exidx sections by order of ascending address. This requires the
  // relative positions of InputSections to be known.
  auto compareByFilePosition = [](const InputSection *a,
                                  const InputSection *b) {
    OutputSection *aOut = a->getParent();
    OutputSection *bOut = b->getParent();

    if (aOut != bOut)
      return aOut->sectionIndex < bOut->sectionIndex;
    return a->outSecOff < b->outSecOff;
  };
  llvm::stable_sort(executableSections, compareByFilePosition);
  sentinel = executableSections.back();
  // Optionally merge adjacent duplicate entries.
  if (config->mergeArmExidx) {
    std::vector<InputSection *> selectedSections;
    selectedSections.reserve(executableSections.size());
    selectedSections.push_back(executableSections[0]);
    size_t prev = 0;
    for (size_t i = 1; i < executableSections.size(); ++i) {
      InputSection *ex1 = findExidxSection(executableSections[prev]);
      InputSection *ex2 = findExidxSection(executableSections[i]);
      if (!isDuplicateArmExidxSec(ex1, ex2)) {
        selectedSections.push_back(executableSections[i]);
        prev = i;
      }
    }
    executableSections = std::move(selectedSections);
  }

  size_t offset = 0;
  size = 0;
  for (InputSection *isec : executableSections) {
    if (InputSection *d = findExidxSection(isec)) {
      d->outSecOff = offset;
      d->parent = getParent();
      offset += d->getSize();
    } else {
      offset += 8;
    }
  }
  // Size includes Sentinel.
  size = offset + 8;
}

InputSection *ARMExidxSyntheticSection::getLinkOrderDep() const {
  return executableSections.front();
}

// To write the .ARM.exidx table from the ExecutableSections we have three cases
// 1.) The InputSection has a .ARM.exidx InputSection in its dependent sections.
//     We write the .ARM.exidx section contents and apply its relocations.
// 2.) The InputSection does not have a dependent .ARM.exidx InputSection. We
//     must write the contents of an EXIDX_CANTUNWIND directly. We use the
//     start of the InputSection as the purpose of the linker generated
//     section is to terminate the address range of the previous entry.
// 3.) A trailing EXIDX_CANTUNWIND sentinel section is required at the end of
//     the table to terminate the address range of the final entry.
void ARMExidxSyntheticSection::writeTo(uint8_t *buf) {

  const uint8_t cantUnwindData[8] = {0, 0, 0, 0,  // PREL31 to target
                                     1, 0, 0, 0}; // EXIDX_CANTUNWIND

  uint64_t offset = 0;
  for (InputSection *isec : executableSections) {
    assert(isec->getParent() != nullptr);
    if (InputSection *d = findExidxSection(isec)) {
      memcpy(buf + offset, d->data().data(), d->data().size());
      d->relocateAlloc(buf, buf + d->getSize());
      offset += d->getSize();
    } else {
      // A Linker generated CANTUNWIND section.
      memcpy(buf + offset, cantUnwindData, sizeof(cantUnwindData));
      uint64_t s = isec->getVA();
      uint64_t p = getVA() + offset;
      target->relocateOne(buf + offset, R_ARM_PREL31, s - p);
      offset += 8;
    }
  }
  // Write Sentinel.
  memcpy(buf + offset, cantUnwindData, sizeof(cantUnwindData));
  uint64_t s = sentinel->getVA(sentinel->getSize());
  uint64_t p = getVA() + offset;
  target->relocateOne(buf + offset, R_ARM_PREL31, s - p);
  assert(size == offset + 8);
}

bool ARMExidxSyntheticSection::classof(const SectionBase *d) {
  return d->kind() == InputSectionBase::Synthetic && d->type == SHT_ARM_EXIDX;
}

ThunkSection::ThunkSection(OutputSection *os, uint64_t off)
    : SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS,
                       config->wordsize, ".text.thunk") {
  this->parent = os;
  this->outSecOff = off;
}

void ThunkSection::addThunk(Thunk *t) {
  thunks.push_back(t);
  t->addSymbols(*this);
}

void ThunkSection::writeTo(uint8_t *buf) {
  for (Thunk *t : thunks)
    t->writeTo(buf + t->offset);
}

InputSection *ThunkSection::getTargetInputSection() const {
  if (thunks.empty())
    return nullptr;
  const Thunk *t = thunks.front();
  return t->getTargetInputSection();
}

bool ThunkSection::assignOffsets() {
  uint64_t off = 0;
  for (Thunk *t : thunks) {
    off = alignTo(off, t->alignment);
    t->setOffset(off);
    uint32_t size = t->size();
    t->getThunkTargetSym()->size = size;
    off += size;
  }
  bool changed = off != size;
  size = off;
  return changed;
}

PPC32Got2Section::PPC32Got2Section()
    : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS, 4, ".got2") {}

bool PPC32Got2Section::isNeeded() const {
  // See the comment below. This is not needed if there is no other
  // InputSection.
  for (BaseCommand *base : getParent()->sectionCommands)
    if (auto *isd = dyn_cast<InputSectionDescription>(base))
      for (InputSection *isec : isd->sections)
        if (isec != this)
          return true;
  return false;
}

void PPC32Got2Section::finalizeContents() {
  // PPC32 may create multiple GOT sections for -fPIC/-fPIE, one per file in
  // .got2 . This function computes outSecOff of each .got2 to be used in
  // PPC32PltCallStub::writeTo(). The purpose of this empty synthetic section is
  // to collect input sections named ".got2".
  uint32_t offset = 0;
  for (BaseCommand *base : getParent()->sectionCommands)
    if (auto *isd = dyn_cast<InputSectionDescription>(base)) {
      for (InputSection *isec : isd->sections) {
        if (isec == this)
          continue;
        isec->file->ppc32Got2OutSecOff = offset;
        offset += (uint32_t)isec->getSize();
      }
    }
}

// If linking position-dependent code then the table will store the addresses
// directly in the binary so the section has type SHT_PROGBITS. If linking
// position-independent code the section has type SHT_NOBITS since it will be
// allocated and filled in by the dynamic linker.
PPC64LongBranchTargetSection::PPC64LongBranchTargetSection()
    : SyntheticSection(SHF_ALLOC | SHF_WRITE,
                       config->isPic ? SHT_NOBITS : SHT_PROGBITS, 8,
                       ".branch_lt") {}

void PPC64LongBranchTargetSection::addEntry(Symbol &sym) {
  assert(sym.ppc64BranchltIndex == 0xffff);
  sym.ppc64BranchltIndex = entries.size();
  entries.push_back(&sym);
}

size_t PPC64LongBranchTargetSection::getSize() const {
  return entries.size() * 8;
}

void PPC64LongBranchTargetSection::writeTo(uint8_t *buf) {
  // If linking non-pic we have the final addresses of the targets and they get
  // written to the table directly. For pic the dynamic linker will allocate
  // the section and fill it it.
  if (config->isPic)
    return;

  for (const Symbol *sym : entries) {
    assert(sym->getVA());
    // Need calls to branch to the local entry-point since a long-branch
    // must be a local-call.
    write64(buf,
            sym->getVA() + getPPC64GlobalEntryToLocalEntryOffset(sym->stOther));
    buf += 8;
  }
}

bool PPC64LongBranchTargetSection::isNeeded() const {
  // `removeUnusedSyntheticSections()` is called before thunk allocation which
  // is too early to determine if this section will be empty or not. We need
  // Finalized to keep the section alive until after thunk creation. Finalized
  // only gets set to true once `finalizeSections()` is called after thunk
  // creation. Becuase of this, if we don't create any long-branch thunks we end
  // up with an empty .branch_lt section in the binary.
  return !finalized || !entries.empty();
}

RISCVSdataSection::RISCVSdataSection()
    : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS, 1, ".sdata") {}

bool RISCVSdataSection::isNeeded() const {
  if (!ElfSym::riscvGlobalPointer)
    return false;

  // __global_pointer$ is defined relative to .sdata . If the section does not
  // exist, create a dummy one.
  for (BaseCommand *base : getParent()->sectionCommands)
    if (auto *isd = dyn_cast<InputSectionDescription>(base))
      for (InputSection *isec : isd->sections)
        if (isec != this)
          return false;
  return true;
}

static uint8_t getAbiVersion() {
  // MIPS non-PIC executable gets ABI version 1.
  if (config->emachine == EM_MIPS) {
    if (!config->isPic && !config->relocatable &&
        (config->eflags & (EF_MIPS_PIC | EF_MIPS_CPIC)) == EF_MIPS_CPIC)
      return 1;
    return 0;
  }

  if (config->emachine == EM_AMDGPU) {
    uint8_t ver = objectFiles[0]->abiVersion;
    for (InputFile *file : makeArrayRef(objectFiles).slice(1))
      if (file->abiVersion != ver)
        error("incompatible ABI version: " + toString(file));
    return ver;
  }

  return 0;
}

template <typename ELFT> void elf::writeEhdr(uint8_t *buf, Partition &part) {
  // For executable segments, the trap instructions are written before writing
  // the header. Setting Elf header bytes to zero ensures that any unused bytes
  // in header are zero-cleared, instead of having trap instructions.
  memset(buf, 0, sizeof(typename ELFT::Ehdr));
  memcpy(buf, "\177ELF", 4);

  auto *eHdr = reinterpret_cast<typename ELFT::Ehdr *>(buf);
  eHdr->e_ident[EI_CLASS] = config->is64 ? ELFCLASS64 : ELFCLASS32;
  eHdr->e_ident[EI_DATA] = config->isLE ? ELFDATA2LSB : ELFDATA2MSB;
  eHdr->e_ident[EI_VERSION] = EV_CURRENT;
  eHdr->e_ident[EI_OSABI] = config->osabi;
  eHdr->e_ident[EI_ABIVERSION] = getAbiVersion();
  eHdr->e_machine = config->emachine;
  eHdr->e_version = EV_CURRENT;
  eHdr->e_flags = config->eflags;
  eHdr->e_ehsize = sizeof(typename ELFT::Ehdr);
  eHdr->e_phnum = part.phdrs.size();
  eHdr->e_shentsize = sizeof(typename ELFT::Shdr);

  if (!config->relocatable) {
    eHdr->e_phoff = sizeof(typename ELFT::Ehdr);
    eHdr->e_phentsize = sizeof(typename ELFT::Phdr);
  }
}

template <typename ELFT> void elf::writePhdrs(uint8_t *buf, Partition &part) {
  // Write the program header table.
  auto *hBuf = reinterpret_cast<typename ELFT::Phdr *>(buf);
  for (PhdrEntry *p : part.phdrs) {
    hBuf->p_type = p->p_type;
    hBuf->p_flags = p->p_flags;
    hBuf->p_offset = p->p_offset;
    hBuf->p_vaddr = p->p_vaddr;
    hBuf->p_paddr = p->p_paddr;
    hBuf->p_filesz = p->p_filesz;
    hBuf->p_memsz = p->p_memsz;
    hBuf->p_align = p->p_align;
    ++hBuf;
  }
}

template <typename ELFT>
PartitionElfHeaderSection<ELFT>::PartitionElfHeaderSection()
    : SyntheticSection(SHF_ALLOC, SHT_LLVM_PART_EHDR, 1, "") {}

template <typename ELFT>
size_t PartitionElfHeaderSection<ELFT>::getSize() const {
  return sizeof(typename ELFT::Ehdr);
}

template <typename ELFT>
void PartitionElfHeaderSection<ELFT>::writeTo(uint8_t *buf) {
  writeEhdr<ELFT>(buf, getPartition());

  // Loadable partitions are always ET_DYN.
  auto *eHdr = reinterpret_cast<typename ELFT::Ehdr *>(buf);
  eHdr->e_type = ET_DYN;
}

template <typename ELFT>
PartitionProgramHeadersSection<ELFT>::PartitionProgramHeadersSection()
    : SyntheticSection(SHF_ALLOC, SHT_LLVM_PART_PHDR, 1, ".phdrs") {}

template <typename ELFT>
size_t PartitionProgramHeadersSection<ELFT>::getSize() const {
  return sizeof(typename ELFT::Phdr) * getPartition().phdrs.size();
}

template <typename ELFT>
void PartitionProgramHeadersSection<ELFT>::writeTo(uint8_t *buf) {
  writePhdrs<ELFT>(buf, getPartition());
}

PartitionIndexSection::PartitionIndexSection()
    : SyntheticSection(SHF_ALLOC, SHT_PROGBITS, 4, ".rodata") {}

size_t PartitionIndexSection::getSize() const {
  return 12 * (partitions.size() - 1);
}

void PartitionIndexSection::finalizeContents() {
  for (size_t i = 1; i != partitions.size(); ++i)
    partitions[i].nameStrTab = mainPart->dynStrTab->addString(partitions[i].name);
}

void PartitionIndexSection::writeTo(uint8_t *buf) {
  uint64_t va = getVA();
  for (size_t i = 1; i != partitions.size(); ++i) {
    write32(buf, mainPart->dynStrTab->getVA() + partitions[i].nameStrTab - va);
    write32(buf + 4, partitions[i].elfHeader->getVA() - (va + 4));

    SyntheticSection *next =
        i == partitions.size() - 1 ? in.partEnd : partitions[i + 1].elfHeader;
    write32(buf + 8, next->getVA() - partitions[i].elfHeader->getVA());

    va += 12;
    buf += 12;
  }
}

InStruct elf::in;

std::vector<Partition> elf::partitions;
Partition *elf::mainPart;

template GdbIndexSection *GdbIndexSection::create<ELF32LE>();
template GdbIndexSection *GdbIndexSection::create<ELF32BE>();
template GdbIndexSection *GdbIndexSection::create<ELF64LE>();
template GdbIndexSection *GdbIndexSection::create<ELF64BE>();

template void elf::splitSections<ELF32LE>();
template void elf::splitSections<ELF32BE>();
template void elf::splitSections<ELF64LE>();
template void elf::splitSections<ELF64BE>();

template void EhFrameSection::addSection<ELF32LE>(InputSectionBase *);
template void EhFrameSection::addSection<ELF32BE>(InputSectionBase *);
template void EhFrameSection::addSection<ELF64LE>(InputSectionBase *);
template void EhFrameSection::addSection<ELF64BE>(InputSectionBase *);

template void PltSection::addEntry<ELF32LE>(Symbol &Sym);
template void PltSection::addEntry<ELF32BE>(Symbol &Sym);
template void PltSection::addEntry<ELF64LE>(Symbol &Sym);
template void PltSection::addEntry<ELF64BE>(Symbol &Sym);

template class elf::MipsAbiFlagsSection<ELF32LE>;
template class elf::MipsAbiFlagsSection<ELF32BE>;
template class elf::MipsAbiFlagsSection<ELF64LE>;
template class elf::MipsAbiFlagsSection<ELF64BE>;

template class elf::MipsOptionsSection<ELF32LE>;
template class elf::MipsOptionsSection<ELF32BE>;
template class elf::MipsOptionsSection<ELF64LE>;
template class elf::MipsOptionsSection<ELF64BE>;

template class elf::MipsReginfoSection<ELF32LE>;
template class elf::MipsReginfoSection<ELF32BE>;
template class elf::MipsReginfoSection<ELF64LE>;
template class elf::MipsReginfoSection<ELF64BE>;

template class elf::DynamicSection<ELF32LE>;
template class elf::DynamicSection<ELF32BE>;
template class elf::DynamicSection<ELF64LE>;
template class elf::DynamicSection<ELF64BE>;

template class elf::RelocationSection<ELF32LE>;
template class elf::RelocationSection<ELF32BE>;
template class elf::RelocationSection<ELF64LE>;
template class elf::RelocationSection<ELF64BE>;

template class elf::AndroidPackedRelocationSection<ELF32LE>;
template class elf::AndroidPackedRelocationSection<ELF32BE>;
template class elf::AndroidPackedRelocationSection<ELF64LE>;
template class elf::AndroidPackedRelocationSection<ELF64BE>;

template class elf::RelrSection<ELF32LE>;
template class elf::RelrSection<ELF32BE>;
template class elf::RelrSection<ELF64LE>;
template class elf::RelrSection<ELF64BE>;

template class elf::SymbolTableSection<ELF32LE>;
template class elf::SymbolTableSection<ELF32BE>;
template class elf::SymbolTableSection<ELF64LE>;
template class elf::SymbolTableSection<ELF64BE>;

template class elf::VersionNeedSection<ELF32LE>;
template class elf::VersionNeedSection<ELF32BE>;
template class elf::VersionNeedSection<ELF64LE>;
template class elf::VersionNeedSection<ELF64BE>;

template void elf::writeEhdr<ELF32LE>(uint8_t *Buf, Partition &Part);
template void elf::writeEhdr<ELF32BE>(uint8_t *Buf, Partition &Part);
template void elf::writeEhdr<ELF64LE>(uint8_t *Buf, Partition &Part);
template void elf::writeEhdr<ELF64BE>(uint8_t *Buf, Partition &Part);

template void elf::writePhdrs<ELF32LE>(uint8_t *Buf, Partition &Part);
template void elf::writePhdrs<ELF32BE>(uint8_t *Buf, Partition &Part);
template void elf::writePhdrs<ELF64LE>(uint8_t *Buf, Partition &Part);
template void elf::writePhdrs<ELF64BE>(uint8_t *Buf, Partition &Part);

template class elf::PartitionElfHeaderSection<ELF32LE>;
template class elf::PartitionElfHeaderSection<ELF32BE>;
template class elf::PartitionElfHeaderSection<ELF64LE>;
template class elf::PartitionElfHeaderSection<ELF64BE>;

template class elf::PartitionProgramHeadersSection<ELF32LE>;
template class elf::PartitionProgramHeadersSection<ELF32BE>;
template class elf::PartitionProgramHeadersSection<ELF64LE>;
template class elf::PartitionProgramHeadersSection<ELF64BE>;