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
use rustc::middle::cstore::{EncodedMetadata, LibSource, NativeLibrary, NativeLibraryKind};
use rustc::middle::dependency_format::Linkage;
use rustc::session::config::{
    self, CFGuard, DebugInfo, OutputFilenames, OutputType, PrintRequest, Sanitizer,
};
use rustc::session::search_paths::PathKind;
/// For all the linkers we support, and information they might
/// need out of the shared crate context before we get rid of it.
use rustc::session::{filesearch, Session};
use rustc_data_structures::fx::FxHashSet;
use rustc_fs_util::fix_windows_verbatim_for_gcc;
use rustc_hir::def_id::CrateNum;
use rustc_span::symbol::Symbol;
use rustc_target::spec::{LinkerFlavor, PanicStrategy, RelroLevel};

use super::archive::ArchiveBuilder;
use super::command::Command;
use super::linker::Linker;
use super::rpath::{self, RPathConfig};
use crate::{
    looks_like_rust_object_file, CodegenResults, CrateInfo, METADATA_FILENAME,
    RLIB_BYTECODE_EXTENSION,
};

use cc::windows_registry;
use tempfile::{Builder as TempFileBuilder, TempDir};

use std::ascii;
use std::char;
use std::env;
use std::ffi::OsString;
use std::fmt;
use std::fs;
use std::io;
use std::path::{Path, PathBuf};
use std::process::{ExitStatus, Output, Stdio};
use std::str;

pub use rustc_codegen_utils::link::*;

pub fn remove(sess: &Session, path: &Path) {
    if let Err(e) = fs::remove_file(path) {
        sess.err(&format!("failed to remove {}: {}", path.display(), e));
    }
}

/// Performs the linkage portion of the compilation phase. This will generate all
/// of the requested outputs for this compilation session.
pub fn link_binary<'a, B: ArchiveBuilder<'a>>(
    sess: &'a Session,
    codegen_results: &CodegenResults,
    outputs: &OutputFilenames,
    crate_name: &str,
    target_cpu: &str,
) {
    let _timer = sess.timer("link_binary");
    let output_metadata = sess.opts.output_types.contains_key(&OutputType::Metadata);
    for &crate_type in sess.crate_types.borrow().iter() {
        // Ignore executable crates if we have -Z no-codegen, as they will error.
        if (sess.opts.debugging_opts.no_codegen || !sess.opts.output_types.should_codegen())
            && !output_metadata
            && crate_type == config::CrateType::Executable
        {
            continue;
        }

        if invalid_output_for_target(sess, crate_type) {
            bug!(
                "invalid output type `{:?}` for target os `{}`",
                crate_type,
                sess.opts.target_triple
            );
        }

        sess.time("link_binary_check_files_are_writeable", || {
            for obj in codegen_results.modules.iter().filter_map(|m| m.object.as_ref()) {
                check_file_is_writeable(obj, sess);
            }
        });

        let tmpdir = TempFileBuilder::new()
            .prefix("rustc")
            .tempdir()
            .unwrap_or_else(|err| sess.fatal(&format!("couldn't create a temp dir: {}", err)));

        if outputs.outputs.should_codegen() {
            let out_filename = out_filename(sess, crate_type, outputs, crate_name);
            match crate_type {
                config::CrateType::Rlib => {
                    let _timer = sess.timer("link_rlib");
                    link_rlib::<B>(
                        sess,
                        codegen_results,
                        RlibFlavor::Normal,
                        &out_filename,
                        &tmpdir,
                    )
                    .build();
                }
                config::CrateType::Staticlib => {
                    link_staticlib::<B>(sess, codegen_results, &out_filename, &tmpdir);
                }
                _ => {
                    link_natively::<B>(
                        sess,
                        crate_type,
                        &out_filename,
                        codegen_results,
                        tmpdir.path(),
                        target_cpu,
                    );
                }
            }
            if sess.opts.json_artifact_notifications {
                sess.parse_sess.span_diagnostic.emit_artifact_notification(&out_filename, "link");
            }
        }

        if sess.opts.cg.save_temps {
            let _ = tmpdir.into_path();
        }
    }

    // Remove the temporary object file and metadata if we aren't saving temps
    sess.time("link_binary_remove_temps", || {
        if !sess.opts.cg.save_temps {
            if sess.opts.output_types.should_codegen()
                && !preserve_objects_for_their_debuginfo(sess)
            {
                for obj in codegen_results.modules.iter().filter_map(|m| m.object.as_ref()) {
                    remove(sess, obj);
                }
            }
            for obj in codegen_results.modules.iter().filter_map(|m| m.bytecode_compressed.as_ref())
            {
                remove(sess, obj);
            }
            if let Some(ref metadata_module) = codegen_results.metadata_module {
                if let Some(ref obj) = metadata_module.object {
                    remove(sess, obj);
                }
            }
            if let Some(ref allocator_module) = codegen_results.allocator_module {
                if let Some(ref obj) = allocator_module.object {
                    remove(sess, obj);
                }
                if let Some(ref bc) = allocator_module.bytecode_compressed {
                    remove(sess, bc);
                }
            }
        }
    });
}

// The third parameter is for env vars, used on windows to set up the
// path for MSVC to find its DLLs, and gcc to find its bundled
// toolchain
pub fn get_linker(sess: &Session, linker: &Path, flavor: LinkerFlavor) -> (PathBuf, Command) {
    let msvc_tool = windows_registry::find_tool(&sess.opts.target_triple.triple(), "link.exe");

    // If our linker looks like a batch script on Windows then to execute this
    // we'll need to spawn `cmd` explicitly. This is primarily done to handle
    // emscripten where the linker is `emcc.bat` and needs to be spawned as
    // `cmd /c emcc.bat ...`.
    //
    // This worked historically but is needed manually since #42436 (regression
    // was tagged as #42791) and some more info can be found on #44443 for
    // emscripten itself.
    let mut cmd = match linker.to_str() {
        Some(linker) if cfg!(windows) && linker.ends_with(".bat") => Command::bat_script(linker),
        _ => match flavor {
            LinkerFlavor::Lld(f) => Command::lld(linker, f),
            LinkerFlavor::Msvc
                if sess.opts.cg.linker.is_none() && sess.target.target.options.linker.is_none() =>
            {
                Command::new(msvc_tool.as_ref().map(|t| t.path()).unwrap_or(linker))
            }
            _ => Command::new(linker),
        },
    };

    // UWP apps have API restrictions enforced during Store submissions.
    // To comply with the Windows App Certification Kit,
    // MSVC needs to link with the Store versions of the runtime libraries (vcruntime, msvcrt, etc).
    let t = &sess.target.target;
    if flavor == LinkerFlavor::Msvc && t.target_vendor == "uwp" {
        if let Some(ref tool) = msvc_tool {
            let original_path = tool.path();
            if let Some(ref root_lib_path) = original_path.ancestors().skip(4).next() {
                let arch = match t.arch.as_str() {
                    "x86_64" => Some("x64".to_string()),
                    "x86" => Some("x86".to_string()),
                    "aarch64" => Some("arm64".to_string()),
                    _ => None,
                };
                if let Some(ref a) = arch {
                    let mut arg = OsString::from("/LIBPATH:");
                    arg.push(format!("{}\\lib\\{}\\store", root_lib_path.display(), a.to_string()));
                    cmd.arg(&arg);
                } else {
                    warn!("arch is not supported");
                }
            } else {
                warn!("MSVC root path lib location not found");
            }
        } else {
            warn!("link.exe not found");
        }
    }

    // The compiler's sysroot often has some bundled tools, so add it to the
    // PATH for the child.
    let mut new_path = sess.host_filesearch(PathKind::All).get_tools_search_paths();
    let mut msvc_changed_path = false;
    if sess.target.target.options.is_like_msvc {
        if let Some(ref tool) = msvc_tool {
            cmd.args(tool.args());
            for &(ref k, ref v) in tool.env() {
                if k == "PATH" {
                    new_path.extend(env::split_paths(v));
                    msvc_changed_path = true;
                } else {
                    cmd.env(k, v);
                }
            }
        }
    }

    if !msvc_changed_path {
        if let Some(path) = env::var_os("PATH") {
            new_path.extend(env::split_paths(&path));
        }
    }
    cmd.env("PATH", env::join_paths(new_path).unwrap());

    (linker.to_path_buf(), cmd)
}

pub fn each_linked_rlib(
    info: &CrateInfo,
    f: &mut dyn FnMut(CrateNum, &Path),
) -> Result<(), String> {
    let crates = info.used_crates_static.iter();
    let mut fmts = None;
    for (ty, list) in info.dependency_formats.iter() {
        match ty {
            config::CrateType::Executable
            | config::CrateType::Staticlib
            | config::CrateType::Cdylib
            | config::CrateType::ProcMacro => {
                fmts = Some(list);
                break;
            }
            _ => {}
        }
    }
    let fmts = match fmts {
        Some(f) => f,
        None => return Err("could not find formats for rlibs".to_string()),
    };
    for &(cnum, ref path) in crates {
        match fmts.get(cnum.as_usize() - 1) {
            Some(&Linkage::NotLinked) | Some(&Linkage::IncludedFromDylib) => continue,
            Some(_) => {}
            None => return Err("could not find formats for rlibs".to_string()),
        }
        let name = &info.crate_name[&cnum];
        let path = match *path {
            LibSource::Some(ref p) => p,
            LibSource::MetadataOnly => {
                return Err(format!(
                    "could not find rlib for: `{}`, found rmeta (metadata) file",
                    name
                ));
            }
            LibSource::None => return Err(format!("could not find rlib for: `{}`", name)),
        };
        f(cnum, &path);
    }
    Ok(())
}

/// We use a temp directory here to avoid races between concurrent rustc processes,
/// such as builds in the same directory using the same filename for metadata while
/// building an `.rlib` (stomping over one another), or writing an `.rmeta` into a
/// directory being searched for `extern crate` (observing an incomplete file).
/// The returned path is the temporary file containing the complete metadata.
pub fn emit_metadata<'a>(
    sess: &'a Session,
    metadata: &EncodedMetadata,
    tmpdir: &TempDir,
) -> PathBuf {
    let out_filename = tmpdir.path().join(METADATA_FILENAME);
    let result = fs::write(&out_filename, &metadata.raw_data);

    if let Err(e) = result {
        sess.fatal(&format!("failed to write {}: {}", out_filename.display(), e));
    }

    out_filename
}

// Create an 'rlib'
//
// An rlib in its current incarnation is essentially a renamed .a file. The
// rlib primarily contains the object file of the crate, but it also contains
// all of the object files from native libraries. This is done by unzipping
// native libraries and inserting all of the contents into this archive.
fn link_rlib<'a, B: ArchiveBuilder<'a>>(
    sess: &'a Session,
    codegen_results: &CodegenResults,
    flavor: RlibFlavor,
    out_filename: &Path,
    tmpdir: &TempDir,
) -> B {
    info!("preparing rlib to {:?}", out_filename);
    let mut ab = <B as ArchiveBuilder>::new(sess, out_filename, None);

    for obj in codegen_results.modules.iter().filter_map(|m| m.object.as_ref()) {
        ab.add_file(obj);
    }

    // Note that in this loop we are ignoring the value of `lib.cfg`. That is,
    // we may not be configured to actually include a static library if we're
    // adding it here. That's because later when we consume this rlib we'll
    // decide whether we actually needed the static library or not.
    //
    // To do this "correctly" we'd need to keep track of which libraries added
    // which object files to the archive. We don't do that here, however. The
    // #[link(cfg(..))] feature is unstable, though, and only intended to get
    // liblibc working. In that sense the check below just indicates that if
    // there are any libraries we want to omit object files for at link time we
    // just exclude all custom object files.
    //
    // Eventually if we want to stabilize or flesh out the #[link(cfg(..))]
    // feature then we'll need to figure out how to record what objects were
    // loaded from the libraries found here and then encode that into the
    // metadata of the rlib we're generating somehow.
    for lib in codegen_results.crate_info.used_libraries.iter() {
        match lib.kind {
            NativeLibraryKind::NativeStatic => {}
            NativeLibraryKind::NativeStaticNobundle
            | NativeLibraryKind::NativeFramework
            | NativeLibraryKind::NativeRawDylib
            | NativeLibraryKind::NativeUnknown => continue,
        }
        if let Some(name) = lib.name {
            ab.add_native_library(name);
        }
    }

    // After adding all files to the archive, we need to update the
    // symbol table of the archive.
    ab.update_symbols();

    // Note that it is important that we add all of our non-object "magical
    // files" *after* all of the object files in the archive. The reason for
    // this is as follows:
    //
    // * When performing LTO, this archive will be modified to remove
    //   objects from above. The reason for this is described below.
    //
    // * When the system linker looks at an archive, it will attempt to
    //   determine the architecture of the archive in order to see whether its
    //   linkable.
    //
    //   The algorithm for this detection is: iterate over the files in the
    //   archive. Skip magical SYMDEF names. Interpret the first file as an
    //   object file. Read architecture from the object file.
    //
    // * As one can probably see, if "metadata" and "foo.bc" were placed
    //   before all of the objects, then the architecture of this archive would
    //   not be correctly inferred once 'foo.o' is removed.
    //
    // Basically, all this means is that this code should not move above the
    // code above.
    match flavor {
        RlibFlavor::Normal => {
            // Instead of putting the metadata in an object file section, rlibs
            // contain the metadata in a separate file.
            ab.add_file(&emit_metadata(sess, &codegen_results.metadata, tmpdir));

            // For LTO purposes, the bytecode of this library is also inserted
            // into the archive.
            for bytecode in
                codegen_results.modules.iter().filter_map(|m| m.bytecode_compressed.as_ref())
            {
                ab.add_file(bytecode);
            }

            // After adding all files to the archive, we need to update the
            // symbol table of the archive. This currently dies on macOS (see
            // #11162), and isn't necessary there anyway
            if !sess.target.target.options.is_like_osx {
                ab.update_symbols();
            }
        }

        RlibFlavor::StaticlibBase => {
            let obj = codegen_results.allocator_module.as_ref().and_then(|m| m.object.as_ref());
            if let Some(obj) = obj {
                ab.add_file(obj);
            }
        }
    }

    ab
}

// Create a static archive
//
// This is essentially the same thing as an rlib, but it also involves adding
// all of the upstream crates' objects into the archive. This will slurp in
// all of the native libraries of upstream dependencies as well.
//
// Additionally, there's no way for us to link dynamic libraries, so we warn
// about all dynamic library dependencies that they're not linked in.
//
// There's no need to include metadata in a static archive, so ensure to not
// link in the metadata object file (and also don't prepare the archive with a
// metadata file).
fn link_staticlib<'a, B: ArchiveBuilder<'a>>(
    sess: &'a Session,
    codegen_results: &CodegenResults,
    out_filename: &Path,
    tempdir: &TempDir,
) {
    let mut ab =
        link_rlib::<B>(sess, codegen_results, RlibFlavor::StaticlibBase, out_filename, tempdir);
    let mut all_native_libs = vec![];

    let res = each_linked_rlib(&codegen_results.crate_info, &mut |cnum, path| {
        let name = &codegen_results.crate_info.crate_name[&cnum];
        let native_libs = &codegen_results.crate_info.native_libraries[&cnum];

        // Here when we include the rlib into our staticlib we need to make a
        // decision whether to include the extra object files along the way.
        // These extra object files come from statically included native
        // libraries, but they may be cfg'd away with #[link(cfg(..))].
        //
        // This unstable feature, though, only needs liblibc to work. The only
        // use case there is where musl is statically included in liblibc.rlib,
        // so if we don't want the included version we just need to skip it. As
        // a result the logic here is that if *any* linked library is cfg'd away
        // we just skip all object files.
        //
        // Clearly this is not sufficient for a general purpose feature, and
        // we'd want to read from the library's metadata to determine which
        // object files come from where and selectively skip them.
        let skip_object_files = native_libs
            .iter()
            .any(|lib| lib.kind == NativeLibraryKind::NativeStatic && !relevant_lib(sess, lib));
        ab.add_rlib(
            path,
            &name.as_str(),
            are_upstream_rust_objects_already_included(sess)
                && !ignored_for_lto(sess, &codegen_results.crate_info, cnum),
            skip_object_files,
        )
        .unwrap();

        all_native_libs.extend(codegen_results.crate_info.native_libraries[&cnum].iter().cloned());
    });
    if let Err(e) = res {
        sess.fatal(&e);
    }

    ab.update_symbols();
    ab.build();

    if !all_native_libs.is_empty() {
        if sess.opts.prints.contains(&PrintRequest::NativeStaticLibs) {
            print_native_static_libs(sess, &all_native_libs);
        }
    }
}

// Create a dynamic library or executable
//
// This will invoke the system linker/cc to create the resulting file. This
// links to all upstream files as well.
fn link_natively<'a, B: ArchiveBuilder<'a>>(
    sess: &'a Session,
    crate_type: config::CrateType,
    out_filename: &Path,
    codegen_results: &CodegenResults,
    tmpdir: &Path,
    target_cpu: &str,
) {
    info!("preparing {:?} to {:?}", crate_type, out_filename);
    let (linker, flavor) = linker_and_flavor(sess);

    // The invocations of cc share some flags across platforms
    let (pname, mut cmd) = get_linker(sess, &linker, flavor);

    if let Some(args) = sess.target.target.options.pre_link_args.get(&flavor) {
        cmd.args(args);
    }
    if let Some(args) = sess.target.target.options.pre_link_args_crt.get(&flavor) {
        if sess.crt_static() {
            cmd.args(args);
        }
    }
    if let Some(ref args) = sess.opts.debugging_opts.pre_link_args {
        cmd.args(args);
    }
    cmd.args(&sess.opts.debugging_opts.pre_link_arg);

    if sess.target.target.options.is_like_fuchsia {
        let prefix = match sess.opts.debugging_opts.sanitizer {
            Some(Sanitizer::Address) => "asan/",
            _ => "",
        };
        cmd.arg(format!("--dynamic-linker={}ld.so.1", prefix));
    }

    let pre_link_objects = if crate_type == config::CrateType::Executable {
        &sess.target.target.options.pre_link_objects_exe
    } else {
        &sess.target.target.options.pre_link_objects_dll
    };
    for obj in pre_link_objects {
        cmd.arg(get_file_path(sess, obj));
    }

    if crate_type == config::CrateType::Executable && sess.crt_static() {
        for obj in &sess.target.target.options.pre_link_objects_exe_crt {
            cmd.arg(get_file_path(sess, obj));
        }
    }

    if sess.target.target.options.is_like_emscripten {
        cmd.arg("-s");
        cmd.arg(if sess.panic_strategy() == PanicStrategy::Abort {
            "DISABLE_EXCEPTION_CATCHING=1"
        } else {
            "DISABLE_EXCEPTION_CATCHING=0"
        });
    }

    {
        let mut linker = codegen_results.linker_info.to_linker(cmd, &sess, flavor, target_cpu);
        link_sanitizer_runtime(sess, crate_type, &mut *linker);
        link_args::<B>(
            &mut *linker,
            flavor,
            sess,
            crate_type,
            tmpdir,
            out_filename,
            codegen_results,
        );
        cmd = linker.finalize();
    }
    if let Some(args) = sess.target.target.options.late_link_args.get(&flavor) {
        cmd.args(args);
    }
    for obj in &sess.target.target.options.post_link_objects {
        cmd.arg(get_file_path(sess, obj));
    }
    if sess.crt_static() {
        for obj in &sess.target.target.options.post_link_objects_crt {
            cmd.arg(get_file_path(sess, obj));
        }
    }
    if let Some(args) = sess.target.target.options.post_link_args.get(&flavor) {
        cmd.args(args);
    }
    for &(ref k, ref v) in &sess.target.target.options.link_env {
        cmd.env(k, v);
    }
    for k in &sess.target.target.options.link_env_remove {
        cmd.env_remove(k);
    }

    if sess.opts.debugging_opts.print_link_args {
        println!("{:?}", &cmd);
    }

    // May have not found libraries in the right formats.
    sess.abort_if_errors();

    // Invoke the system linker
    info!("{:?}", &cmd);
    let retry_on_segfault = env::var("RUSTC_RETRY_LINKER_ON_SEGFAULT").is_ok();
    let mut prog;
    let mut i = 0;
    loop {
        i += 1;
        prog = sess.time("run_linker", || exec_linker(sess, &mut cmd, out_filename, tmpdir));
        let output = match prog {
            Ok(ref output) => output,
            Err(_) => break,
        };
        if output.status.success() {
            break;
        }
        let mut out = output.stderr.clone();
        out.extend(&output.stdout);
        let out = String::from_utf8_lossy(&out);

        // Check to see if the link failed with "unrecognized command line option:
        // '-no-pie'" for gcc or "unknown argument: '-no-pie'" for clang. If so,
        // reperform the link step without the -no-pie option. This is safe because
        // if the linker doesn't support -no-pie then it should not default to
        // linking executables as pie. Different versions of gcc seem to use
        // different quotes in the error message so don't check for them.
        if sess.target.target.options.linker_is_gnu
            && flavor != LinkerFlavor::Ld
            && (out.contains("unrecognized command line option")
                || out.contains("unknown argument"))
            && out.contains("-no-pie")
            && cmd.get_args().iter().any(|e| e.to_string_lossy() == "-no-pie")
        {
            info!("linker output: {:?}", out);
            warn!("Linker does not support -no-pie command line option. Retrying without.");
            for arg in cmd.take_args() {
                if arg.to_string_lossy() != "-no-pie" {
                    cmd.arg(arg);
                }
            }
            info!("{:?}", &cmd);
            continue;
        }

        // Here's a terribly awful hack that really shouldn't be present in any
        // compiler. Here an environment variable is supported to automatically
        // retry the linker invocation if the linker looks like it segfaulted.
        //
        // Gee that seems odd, normally segfaults are things we want to know
        // about!  Unfortunately though in rust-lang/rust#38878 we're
        // experiencing the linker segfaulting on Travis quite a bit which is
        // causing quite a bit of pain to land PRs when they spuriously fail
        // due to a segfault.
        //
        // The issue #38878 has some more debugging information on it as well,
        // but this unfortunately looks like it's just a race condition in
        // macOS's linker with some thread pool working in the background. It
        // seems that no one currently knows a fix for this so in the meantime
        // we're left with this...
        if !retry_on_segfault || i > 3 {
            break;
        }
        let msg_segv = "clang: error: unable to execute command: Segmentation fault: 11";
        let msg_bus = "clang: error: unable to execute command: Bus error: 10";
        if out.contains(msg_segv) || out.contains(msg_bus) {
            warn!(
                "looks like the linker segfaulted when we tried to call it, \
                 automatically retrying again. cmd = {:?}, out = {}.",
                cmd, out,
            );
            continue;
        }

        if is_illegal_instruction(&output.status) {
            warn!(
                "looks like the linker hit an illegal instruction when we \
                 tried to call it, automatically retrying again. cmd = {:?}, ]\
                 out = {}, status = {}.",
                cmd, out, output.status,
            );
            continue;
        }

        #[cfg(unix)]
        fn is_illegal_instruction(status: &ExitStatus) -> bool {
            use std::os::unix::prelude::*;
            status.signal() == Some(libc::SIGILL)
        }

        #[cfg(windows)]
        fn is_illegal_instruction(_status: &ExitStatus) -> bool {
            false
        }
    }

    match prog {
        Ok(prog) => {
            fn escape_string(s: &[u8]) -> String {
                str::from_utf8(s).map(|s| s.to_owned()).unwrap_or_else(|_| {
                    let mut x = "Non-UTF-8 output: ".to_string();
                    x.extend(s.iter().flat_map(|&b| ascii::escape_default(b)).map(char::from));
                    x
                })
            }
            if !prog.status.success() {
                let mut output = prog.stderr.clone();
                output.extend_from_slice(&prog.stdout);
                sess.struct_err(&format!(
                    "linking with `{}` failed: {}",
                    pname.display(),
                    prog.status
                ))
                .note(&format!("{:?}", &cmd))
                .note(&escape_string(&output))
                .emit();
                sess.abort_if_errors();
            }
            info!("linker stderr:\n{}", escape_string(&prog.stderr));
            info!("linker stdout:\n{}", escape_string(&prog.stdout));
        }
        Err(e) => {
            let linker_not_found = e.kind() == io::ErrorKind::NotFound;

            let mut linker_error = {
                if linker_not_found {
                    sess.struct_err(&format!("linker `{}` not found", pname.display()))
                } else {
                    sess.struct_err(&format!("could not exec the linker `{}`", pname.display()))
                }
            };

            linker_error.note(&e.to_string());

            if !linker_not_found {
                linker_error.note(&format!("{:?}", &cmd));
            }

            linker_error.emit();

            if sess.target.target.options.is_like_msvc && linker_not_found {
                sess.note_without_error(
                    "the msvc targets depend on the msvc linker \
                     but `link.exe` was not found",
                );
                sess.note_without_error(
                    "please ensure that VS 2013, VS 2015, VS 2017 or VS 2019 \
                     was installed with the Visual C++ option",
                );
            }
            sess.abort_if_errors();
        }
    }

    // On macOS, debuggers need this utility to get run to do some munging of
    // the symbols. Note, though, that if the object files are being preserved
    // for their debug information there's no need for us to run dsymutil.
    if sess.target.target.options.is_like_osx
        && sess.opts.debuginfo != DebugInfo::None
        && !preserve_objects_for_their_debuginfo(sess)
    {
        if let Err(e) = Command::new("dsymutil").arg(out_filename).output() {
            sess.fatal(&format!("failed to run dsymutil: {}", e))
        }
    }
}

fn link_sanitizer_runtime(sess: &Session, crate_type: config::CrateType, linker: &mut dyn Linker) {
    let sanitizer = match &sess.opts.debugging_opts.sanitizer {
        Some(s) => s,
        None => return,
    };

    if crate_type != config::CrateType::Executable {
        return;
    }

    let name = match sanitizer {
        Sanitizer::Address => "asan",
        Sanitizer::Leak => "lsan",
        Sanitizer::Memory => "msan",
        Sanitizer::Thread => "tsan",
    };

    let default_sysroot = filesearch::get_or_default_sysroot();
    let default_tlib =
        filesearch::make_target_lib_path(&default_sysroot, sess.opts.target_triple.triple());
    let channel = option_env!("CFG_RELEASE_CHANNEL")
        .map(|channel| format!("-{}", channel))
        .unwrap_or_default();

    match sess.opts.target_triple.triple() {
        "x86_64-apple-darwin" => {
            // On Apple platforms, the sanitizer is always built as a dylib, and
            // LLVM will link to `@rpath/*.dylib`, so we need to specify an
            // rpath to the library as well (the rpath should be absolute, see
            // PR #41352 for details).
            let libname = format!("rustc{}_rt.{}", channel, name);
            let rpath = default_tlib.to_str().expect("non-utf8 component in path");
            linker.args(&["-Wl,-rpath".into(), "-Xlinker".into(), rpath.into()]);
            linker.link_dylib(Symbol::intern(&libname));
        }
        "x86_64-unknown-linux-gnu" | "x86_64-fuchsia" | "aarch64-fuchsia" => {
            let filename = format!("librustc{}_rt.{}.a", channel, name);
            let path = default_tlib.join(&filename);
            linker.link_whole_rlib(&path);
        }
        _ => {}
    }
}

/// Returns a boolean indicating whether the specified crate should be ignored
/// during LTO.
///
/// Crates ignored during LTO are not lumped together in the "massive object
/// file" that we create and are linked in their normal rlib states. See
/// comments below for what crates do not participate in LTO.
///
/// It's unusual for a crate to not participate in LTO. Typically only
/// compiler-specific and unstable crates have a reason to not participate in
/// LTO.
pub fn ignored_for_lto(sess: &Session, info: &CrateInfo, cnum: CrateNum) -> bool {
    // If our target enables builtin function lowering in LLVM then the
    // crates providing these functions don't participate in LTO (e.g.
    // no_builtins or compiler builtins crates).
    !sess.target.target.options.no_builtins
        && (info.compiler_builtins == Some(cnum) || info.is_no_builtins.contains(&cnum))
}

pub fn linker_and_flavor(sess: &Session) -> (PathBuf, LinkerFlavor) {
    fn infer_from(
        sess: &Session,
        linker: Option<PathBuf>,
        flavor: Option<LinkerFlavor>,
    ) -> Option<(PathBuf, LinkerFlavor)> {
        match (linker, flavor) {
            (Some(linker), Some(flavor)) => Some((linker, flavor)),
            // only the linker flavor is known; use the default linker for the selected flavor
            (None, Some(flavor)) => Some((
                PathBuf::from(match flavor {
                    LinkerFlavor::Em => {
                        if cfg!(windows) {
                            "emcc.bat"
                        } else {
                            "emcc"
                        }
                    }
                    LinkerFlavor::Gcc => "cc",
                    LinkerFlavor::Ld => "ld",
                    LinkerFlavor::Msvc => "link.exe",
                    LinkerFlavor::Lld(_) => "lld",
                    LinkerFlavor::PtxLinker => "rust-ptx-linker",
                }),
                flavor,
            )),
            (Some(linker), None) => {
                let stem = linker.file_stem().and_then(|stem| stem.to_str()).unwrap_or_else(|| {
                    sess.fatal("couldn't extract file stem from specified linker")
                });

                let flavor = if stem == "emcc" {
                    LinkerFlavor::Em
                } else if stem == "gcc"
                    || stem.ends_with("-gcc")
                    || stem == "clang"
                    || stem.ends_with("-clang")
                {
                    LinkerFlavor::Gcc
                } else if stem == "ld" || stem == "ld.lld" || stem.ends_with("-ld") {
                    LinkerFlavor::Ld
                } else if stem == "link" || stem == "lld-link" {
                    LinkerFlavor::Msvc
                } else if stem == "lld" || stem == "rust-lld" {
                    LinkerFlavor::Lld(sess.target.target.options.lld_flavor)
                } else {
                    // fall back to the value in the target spec
                    sess.target.target.linker_flavor
                };

                Some((linker, flavor))
            }
            (None, None) => None,
        }
    }

    // linker and linker flavor specified via command line have precedence over what the target
    // specification specifies
    if let Some(ret) = infer_from(sess, sess.opts.cg.linker.clone(), sess.opts.cg.linker_flavor) {
        return ret;
    }

    if let Some(ret) = infer_from(
        sess,
        sess.target.target.options.linker.clone().map(PathBuf::from),
        Some(sess.target.target.linker_flavor),
    ) {
        return ret;
    }

    bug!("Not enough information provided to determine how to invoke the linker");
}

/// Returns a boolean indicating whether we should preserve the object files on
/// the filesystem for their debug information. This is often useful with
/// split-dwarf like schemes.
pub fn preserve_objects_for_their_debuginfo(sess: &Session) -> bool {
    // If the objects don't have debuginfo there's nothing to preserve.
    if sess.opts.debuginfo == config::DebugInfo::None {
        return false;
    }

    // If we're only producing artifacts that are archives, no need to preserve
    // the objects as they're losslessly contained inside the archives.
    let output_linked = sess
        .crate_types
        .borrow()
        .iter()
        .any(|&x| x != config::CrateType::Rlib && x != config::CrateType::Staticlib);
    if !output_linked {
        return false;
    }

    // If we're on OSX then the equivalent of split dwarf is turned on by
    // default. The final executable won't actually have any debug information
    // except it'll have pointers to elsewhere. Historically we've always run
    // `dsymutil` to "link all the dwarf together" but this is actually sort of
    // a bummer for incremental compilation! (the whole point of split dwarf is
    // that you don't do this sort of dwarf link).
    //
    // Basically as a result this just means that if we're on OSX and we're
    // *not* running dsymutil then the object files are the only source of truth
    // for debug information, so we must preserve them.
    if sess.target.target.options.is_like_osx {
        match sess.opts.debugging_opts.run_dsymutil {
            // dsymutil is not being run, preserve objects
            Some(false) => return true,

            // dsymutil is being run, no need to preserve the objects
            Some(true) => return false,

            // The default historical behavior was to always run dsymutil, so
            // we're preserving that temporarily, but we're likely to switch the
            // default soon.
            None => return false,
        }
    }

    false
}

pub fn archive_search_paths(sess: &Session) -> Vec<PathBuf> {
    sess.target_filesearch(PathKind::Native).search_path_dirs()
}

enum RlibFlavor {
    Normal,
    StaticlibBase,
}

pub fn print_native_static_libs(sess: &Session, all_native_libs: &[NativeLibrary]) {
    let lib_args: Vec<_> = all_native_libs
        .iter()
        .filter(|l| relevant_lib(sess, l))
        .filter_map(|lib| {
            let name = lib.name?;
            match lib.kind {
                NativeLibraryKind::NativeStaticNobundle | NativeLibraryKind::NativeUnknown => {
                    if sess.target.target.options.is_like_msvc {
                        Some(format!("{}.lib", name))
                    } else {
                        Some(format!("-l{}", name))
                    }
                }
                NativeLibraryKind::NativeFramework => {
                    // ld-only syntax, since there are no frameworks in MSVC
                    Some(format!("-framework {}", name))
                }
                // These are included, no need to print them
                NativeLibraryKind::NativeStatic | NativeLibraryKind::NativeRawDylib => None,
            }
        })
        .collect();
    if !lib_args.is_empty() {
        sess.note_without_error(
            "Link against the following native artifacts when linking \
                                 against this static library. The order and any duplication \
                                 can be significant on some platforms.",
        );
        // Prefix for greppability
        sess.note_without_error(&format!("native-static-libs: {}", &lib_args.join(" ")));
    }
}

// Because windows-gnu target is meant to be self-contained for pure Rust code it bundles
// own mingw-w64 libraries. These libraries are usually not compatible with mingw-w64
// installed in the system. This breaks many cases where Rust is mixed with other languages
// (e.g. *-sys crates).
// We prefer system mingw-w64 libraries if they are available to avoid this issue.
fn get_crt_libs_path(sess: &Session) -> Option<PathBuf> {
    fn find_exe_in_path<P>(exe_name: P) -> Option<PathBuf>
    where
        P: AsRef<Path>,
    {
        for dir in env::split_paths(&env::var_os("PATH")?) {
            let full_path = dir.join(&exe_name);
            if full_path.is_file() {
                return Some(fix_windows_verbatim_for_gcc(&full_path));
            }
        }
        None
    }

    fn probe(sess: &Session) -> Option<PathBuf> {
        if let (linker, LinkerFlavor::Gcc) = linker_and_flavor(&sess) {
            let linker_path = if cfg!(windows) && linker.extension().is_none() {
                linker.with_extension("exe")
            } else {
                linker
            };
            if let Some(linker_path) = find_exe_in_path(linker_path) {
                let mingw_arch = match &sess.target.target.arch {
                    x if x == "x86" => "i686",
                    x => x,
                };
                let mingw_dir = format!("{}-w64-mingw32", mingw_arch);
                // Here we have path/bin/gcc but we need path/
                let mut path = linker_path;
                path.pop();
                path.pop();
                // Based on Clang MinGW driver
                let probe_path = path.join(&mingw_dir).join("lib");
                if probe_path.exists() {
                    return Some(probe_path);
                };
                let probe_path = path.join(&mingw_dir).join("sys-root/mingw/lib");
                if probe_path.exists() {
                    return Some(probe_path);
                };
            };
        };
        None
    }

    let mut system_library_path = sess.system_library_path.borrow_mut();
    match &*system_library_path {
        Some(Some(compiler_libs_path)) => Some(compiler_libs_path.clone()),
        Some(None) => None,
        None => {
            let path = probe(sess);
            *system_library_path = Some(path.clone());
            path
        }
    }
}

pub fn get_file_path(sess: &Session, name: &str) -> PathBuf {
    // prefer system {,dll}crt2.o libs, see get_crt_libs_path comment for more details
    if sess.target.target.llvm_target.contains("windows-gnu") {
        if let Some(compiler_libs_path) = get_crt_libs_path(sess) {
            let file_path = compiler_libs_path.join(name);
            if file_path.exists() {
                return file_path;
            }
        }
    }
    let fs = sess.target_filesearch(PathKind::Native);
    let file_path = fs.get_lib_path().join(name);
    if file_path.exists() {
        return file_path;
    }
    for search_path in fs.search_paths() {
        let file_path = search_path.dir.join(name);
        if file_path.exists() {
            return file_path;
        }
    }
    PathBuf::from(name)
}

pub fn exec_linker(
    sess: &Session,
    cmd: &mut Command,
    out_filename: &Path,
    tmpdir: &Path,
) -> io::Result<Output> {
    // When attempting to spawn the linker we run a risk of blowing out the
    // size limits for spawning a new process with respect to the arguments
    // we pass on the command line.
    //
    // Here we attempt to handle errors from the OS saying "your list of
    // arguments is too big" by reinvoking the linker again with an `@`-file
    // that contains all the arguments. The theory is that this is then
    // accepted on all linkers and the linker will read all its options out of
    // there instead of looking at the command line.
    if !cmd.very_likely_to_exceed_some_spawn_limit() {
        match cmd.command().stdout(Stdio::piped()).stderr(Stdio::piped()).spawn() {
            Ok(child) => {
                let output = child.wait_with_output();
                flush_linked_file(&output, out_filename)?;
                return output;
            }
            Err(ref e) if command_line_too_big(e) => {
                info!("command line to linker was too big: {}", e);
            }
            Err(e) => return Err(e),
        }
    }

    info!("falling back to passing arguments to linker via an @-file");
    let mut cmd2 = cmd.clone();
    let mut args = String::new();
    for arg in cmd2.take_args() {
        args.push_str(
            &Escape {
                arg: arg.to_str().unwrap(),
                is_like_msvc: sess.target.target.options.is_like_msvc,
            }
            .to_string(),
        );
        args.push_str("\n");
    }
    let file = tmpdir.join("linker-arguments");
    let bytes = if sess.target.target.options.is_like_msvc {
        let mut out = Vec::with_capacity((1 + args.len()) * 2);
        // start the stream with a UTF-16 BOM
        for c in std::iter::once(0xFEFF).chain(args.encode_utf16()) {
            // encode in little endian
            out.push(c as u8);
            out.push((c >> 8) as u8);
        }
        out
    } else {
        args.into_bytes()
    };
    fs::write(&file, &bytes)?;
    cmd2.arg(format!("@{}", file.display()));
    info!("invoking linker {:?}", cmd2);
    let output = cmd2.output();
    flush_linked_file(&output, out_filename)?;
    return output;

    #[cfg(unix)]
    fn flush_linked_file(_: &io::Result<Output>, _: &Path) -> io::Result<()> {
        Ok(())
    }

    #[cfg(windows)]
    fn flush_linked_file(
        command_output: &io::Result<Output>,
        out_filename: &Path,
    ) -> io::Result<()> {
        // On Windows, under high I/O load, output buffers are sometimes not flushed,
        // even long after process exit, causing nasty, non-reproducible output bugs.
        //
        // File::sync_all() calls FlushFileBuffers() down the line, which solves the problem.
        //
        // А full writeup of the original Chrome bug can be found at
        // randomascii.wordpress.com/2018/02/25/compiler-bug-linker-bug-windows-kernel-bug/amp

        if let &Ok(ref out) = command_output {
            if out.status.success() {
                if let Ok(of) = fs::OpenOptions::new().write(true).open(out_filename) {
                    of.sync_all()?;
                }
            }
        }

        Ok(())
    }

    #[cfg(unix)]
    fn command_line_too_big(err: &io::Error) -> bool {
        err.raw_os_error() == Some(::libc::E2BIG)
    }

    #[cfg(windows)]
    fn command_line_too_big(err: &io::Error) -> bool {
        const ERROR_FILENAME_EXCED_RANGE: i32 = 206;
        err.raw_os_error() == Some(ERROR_FILENAME_EXCED_RANGE)
    }

    struct Escape<'a> {
        arg: &'a str,
        is_like_msvc: bool,
    }

    impl<'a> fmt::Display for Escape<'a> {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            if self.is_like_msvc {
                // This is "documented" at
                // https://docs.microsoft.com/en-us/cpp/build/reference/at-specify-a-linker-response-file
                //
                // Unfortunately there's not a great specification of the
                // syntax I could find online (at least) but some local
                // testing showed that this seemed sufficient-ish to catch
                // at least a few edge cases.
                write!(f, "\"")?;
                for c in self.arg.chars() {
                    match c {
                        '"' => write!(f, "\\{}", c)?,
                        c => write!(f, "{}", c)?,
                    }
                }
                write!(f, "\"")?;
            } else {
                // This is documented at https://linux.die.net/man/1/ld, namely:
                //
                // > Options in file are separated by whitespace. A whitespace
                // > character may be included in an option by surrounding the
                // > entire option in either single or double quotes. Any
                // > character (including a backslash) may be included by
                // > prefixing the character to be included with a backslash.
                //
                // We put an argument on each line, so all we need to do is
                // ensure the line is interpreted as one whole argument.
                for c in self.arg.chars() {
                    match c {
                        '\\' | ' ' => write!(f, "\\{}", c)?,
                        c => write!(f, "{}", c)?,
                    }
                }
            }
            Ok(())
        }
    }
}

fn link_args<'a, B: ArchiveBuilder<'a>>(
    cmd: &mut dyn Linker,
    flavor: LinkerFlavor,
    sess: &'a Session,
    crate_type: config::CrateType,
    tmpdir: &Path,
    out_filename: &Path,
    codegen_results: &CodegenResults,
) {
    // Linker plugins should be specified early in the list of arguments
    cmd.linker_plugin_lto();

    // The default library location, we need this to find the runtime.
    // The location of crates will be determined as needed.
    let lib_path = sess.target_filesearch(PathKind::All).get_lib_path();

    // target descriptor
    let t = &sess.target.target;

    // prefer system mingw-w64 libs, see get_crt_libs_path comment for more details
    if cfg!(windows) && sess.target.target.llvm_target.contains("windows-gnu") {
        if let Some(compiler_libs_path) = get_crt_libs_path(sess) {
            cmd.include_path(&compiler_libs_path);
        }
    }

    cmd.include_path(&fix_windows_verbatim_for_gcc(&lib_path));

    for obj in codegen_results.modules.iter().filter_map(|m| m.object.as_ref()) {
        cmd.add_object(obj);
    }
    cmd.output_filename(out_filename);

    if crate_type == config::CrateType::Executable && sess.target.target.options.is_like_windows {
        if let Some(ref s) = codegen_results.windows_subsystem {
            cmd.subsystem(s);
        }
    }

    // If we're building something like a dynamic library then some platforms
    // need to make sure that all symbols are exported correctly from the
    // dynamic library.
    cmd.export_symbols(tmpdir, crate_type);

    // When linking a dynamic library, we put the metadata into a section of the
    // executable. This metadata is in a separate object file from the main
    // object file, so we link that in here.
    if crate_type == config::CrateType::Dylib || crate_type == config::CrateType::ProcMacro {
        let obj = codegen_results.metadata_module.as_ref().and_then(|m| m.object.as_ref());
        if let Some(obj) = obj {
            cmd.add_object(obj);
        }
    }

    let obj = codegen_results.allocator_module.as_ref().and_then(|m| m.object.as_ref());
    if let Some(obj) = obj {
        cmd.add_object(obj);
    }

    // Try to strip as much out of the generated object by removing unused
    // sections if possible. See more comments in linker.rs
    if !sess.opts.cg.link_dead_code {
        let keep_metadata = crate_type == config::CrateType::Dylib;
        cmd.gc_sections(keep_metadata);
    }

    let used_link_args = &codegen_results.crate_info.link_args;

    if crate_type == config::CrateType::Executable {
        let mut position_independent_executable = false;

        if t.options.position_independent_executables {
            let empty_vec = Vec::new();
            let args = sess.opts.cg.link_args.as_ref().unwrap_or(&empty_vec);
            let more_args = &sess.opts.cg.link_arg;
            let mut args = args.iter().chain(more_args.iter()).chain(used_link_args.iter());

            if is_pic(sess) && !sess.crt_static() && !args.any(|x| *x == "-static") {
                position_independent_executable = true;
            }
        }

        if position_independent_executable {
            cmd.position_independent_executable();
        } else {
            // recent versions of gcc can be configured to generate position
            // independent executables by default. We have to pass -no-pie to
            // explicitly turn that off. Not applicable to ld.
            if sess.target.target.options.linker_is_gnu && flavor != LinkerFlavor::Ld {
                cmd.no_position_independent_executable();
            }
        }
    }

    let relro_level = match sess.opts.debugging_opts.relro_level {
        Some(level) => level,
        None => t.options.relro_level,
    };
    match relro_level {
        RelroLevel::Full => {
            cmd.full_relro();
        }
        RelroLevel::Partial => {
            cmd.partial_relro();
        }
        RelroLevel::Off => {
            cmd.no_relro();
        }
        RelroLevel::None => {}
    }

    // Pass optimization flags down to the linker.
    cmd.optimize();

    // Pass debuginfo flags down to the linker.
    cmd.debuginfo();

    // We want to, by default, prevent the compiler from accidentally leaking in
    // any system libraries, so we may explicitly ask linkers to not link to any
    // libraries by default. Note that this does not happen for windows because
    // windows pulls in some large number of libraries and I couldn't quite
    // figure out which subset we wanted.
    //
    // This is all naturally configurable via the standard methods as well.
    if !sess.opts.cg.default_linker_libraries.unwrap_or(false) && t.options.no_default_libraries {
        cmd.no_default_libraries();
    }

    // Take careful note of the ordering of the arguments we pass to the linker
    // here. Linkers will assume that things on the left depend on things to the
    // right. Things on the right cannot depend on things on the left. This is
    // all formally implemented in terms of resolving symbols (libs on the right
    // resolve unknown symbols of libs on the left, but not vice versa).
    //
    // For this reason, we have organized the arguments we pass to the linker as
    // such:
    //
    // 1. The local object that LLVM just generated
    // 2. Local native libraries
    // 3. Upstream rust libraries
    // 4. Upstream native libraries
    //
    // The rationale behind this ordering is that those items lower down in the
    // list can't depend on items higher up in the list. For example nothing can
    // depend on what we just generated (e.g., that'd be a circular dependency).
    // Upstream rust libraries are not allowed to depend on our local native
    // libraries as that would violate the structure of the DAG, in that
    // scenario they are required to link to them as well in a shared fashion.
    //
    // Note that upstream rust libraries may contain native dependencies as
    // well, but they also can't depend on what we just started to add to the
    // link line. And finally upstream native libraries can't depend on anything
    // in this DAG so far because they're only dylibs and dylibs can only depend
    // on other dylibs (e.g., other native deps).
    add_local_native_libraries(cmd, sess, codegen_results);
    add_upstream_rust_crates::<B>(cmd, sess, codegen_results, crate_type, tmpdir);
    add_upstream_native_libraries(cmd, sess, codegen_results, crate_type);

    // Tell the linker what we're doing.
    if crate_type != config::CrateType::Executable {
        cmd.build_dylib(out_filename);
    }
    if crate_type == config::CrateType::Executable && sess.crt_static() {
        cmd.build_static_executable();
    }

    if sess.opts.cg.profile_generate.enabled() {
        cmd.pgo_gen();
    }

    if sess.opts.debugging_opts.control_flow_guard != CFGuard::Disabled {
        cmd.control_flow_guard();
    }

    // FIXME (#2397): At some point we want to rpath our guesses as to
    // where extern libraries might live, based on the
    // addl_lib_search_paths
    if sess.opts.cg.rpath {
        let target_triple = sess.opts.target_triple.triple();
        let mut get_install_prefix_lib_path = || {
            let install_prefix = option_env!("CFG_PREFIX").expect("CFG_PREFIX");
            let tlib = filesearch::relative_target_lib_path(&sess.sysroot, target_triple);
            let mut path = PathBuf::from(install_prefix);
            path.push(&tlib);

            path
        };
        let mut rpath_config = RPathConfig {
            used_crates: &codegen_results.crate_info.used_crates_dynamic,
            out_filename: out_filename.to_path_buf(),
            has_rpath: sess.target.target.options.has_rpath,
            is_like_osx: sess.target.target.options.is_like_osx,
            linker_is_gnu: sess.target.target.options.linker_is_gnu,
            get_install_prefix_lib_path: &mut get_install_prefix_lib_path,
        };
        cmd.args(&rpath::get_rpath_flags(&mut rpath_config));
    }

    // Finally add all the linker arguments provided on the command line along
    // with any #[link_args] attributes found inside the crate
    if let Some(ref args) = sess.opts.cg.link_args {
        cmd.args(args);
    }
    cmd.args(&sess.opts.cg.link_arg);
    cmd.args(&used_link_args);
}

// # Native library linking
//
// User-supplied library search paths (-L on the command line). These are
// the same paths used to find Rust crates, so some of them may have been
// added already by the previous crate linking code. This only allows them
// to be found at compile time so it is still entirely up to outside
// forces to make sure that library can be found at runtime.
//
// Also note that the native libraries linked here are only the ones located
// in the current crate. Upstream crates with native library dependencies
// may have their native library pulled in above.
pub fn add_local_native_libraries(
    cmd: &mut dyn Linker,
    sess: &Session,
    codegen_results: &CodegenResults,
) {
    let filesearch = sess.target_filesearch(PathKind::All);
    for search_path in filesearch.search_paths() {
        match search_path.kind {
            PathKind::Framework => {
                cmd.framework_path(&search_path.dir);
            }
            _ => {
                cmd.include_path(&fix_windows_verbatim_for_gcc(&search_path.dir));
            }
        }
    }

    let relevant_libs =
        codegen_results.crate_info.used_libraries.iter().filter(|l| relevant_lib(sess, l));

    let search_path = archive_search_paths(sess);
    for lib in relevant_libs {
        let name = match lib.name {
            Some(l) => l,
            None => continue,
        };
        match lib.kind {
            NativeLibraryKind::NativeUnknown => cmd.link_dylib(name),
            NativeLibraryKind::NativeFramework => cmd.link_framework(name),
            NativeLibraryKind::NativeStaticNobundle => cmd.link_staticlib(name),
            NativeLibraryKind::NativeStatic => cmd.link_whole_staticlib(name, &search_path),
            NativeLibraryKind::NativeRawDylib => {
                // FIXME(#58713): Proper handling for raw dylibs.
                bug!("raw_dylib feature not yet implemented");
            }
        }
    }
}

// # Rust Crate linking
//
// Rust crates are not considered at all when creating an rlib output. All
// dependencies will be linked when producing the final output (instead of
// the intermediate rlib version)
fn add_upstream_rust_crates<'a, B: ArchiveBuilder<'a>>(
    cmd: &mut dyn Linker,
    sess: &'a Session,
    codegen_results: &CodegenResults,
    crate_type: config::CrateType,
    tmpdir: &Path,
) {
    // All of the heavy lifting has previously been accomplished by the
    // dependency_format module of the compiler. This is just crawling the
    // output of that module, adding crates as necessary.
    //
    // Linking to a rlib involves just passing it to the linker (the linker
    // will slurp up the object files inside), and linking to a dynamic library
    // involves just passing the right -l flag.

    let (_, data) = codegen_results
        .crate_info
        .dependency_formats
        .iter()
        .find(|(ty, _)| *ty == crate_type)
        .expect("failed to find crate type in dependency format list");

    // Invoke get_used_crates to ensure that we get a topological sorting of
    // crates.
    let deps = &codegen_results.crate_info.used_crates_dynamic;

    // There's a few internal crates in the standard library (aka libcore and
    // libstd) which actually have a circular dependence upon one another. This
    // currently arises through "weak lang items" where libcore requires things
    // like `rust_begin_unwind` but libstd ends up defining it. To get this
    // circular dependence to work correctly in all situations we'll need to be
    // sure to correctly apply the `--start-group` and `--end-group` options to
    // GNU linkers, otherwise if we don't use any other symbol from the standard
    // library it'll get discarded and the whole application won't link.
    //
    // In this loop we're calculating the `group_end`, after which crate to
    // pass `--end-group` and `group_start`, before which crate to pass
    // `--start-group`. We currently do this by passing `--end-group` after
    // the first crate (when iterating backwards) that requires a lang item
    // defined somewhere else. Once that's set then when we've defined all the
    // necessary lang items we'll pass `--start-group`.
    //
    // Note that this isn't amazing logic for now but it should do the trick
    // for the current implementation of the standard library.
    let mut group_end = None;
    let mut group_start = None;
    let mut end_with = FxHashSet::default();
    let info = &codegen_results.crate_info;
    for &(cnum, _) in deps.iter().rev() {
        if let Some(missing) = info.missing_lang_items.get(&cnum) {
            end_with.extend(missing.iter().cloned());
            if end_with.len() > 0 && group_end.is_none() {
                group_end = Some(cnum);
            }
        }
        end_with.retain(|item| info.lang_item_to_crate.get(item) != Some(&cnum));
        if end_with.len() == 0 && group_end.is_some() {
            group_start = Some(cnum);
            break;
        }
    }

    // If we didn't end up filling in all lang items from upstream crates then
    // we'll be filling it in with our crate. This probably means we're the
    // standard library itself, so skip this for now.
    if group_end.is_some() && group_start.is_none() {
        group_end = None;
    }

    let mut compiler_builtins = None;

    for &(cnum, _) in deps.iter() {
        if group_start == Some(cnum) {
            cmd.group_start();
        }

        // We may not pass all crates through to the linker. Some crates may
        // appear statically in an existing dylib, meaning we'll pick up all the
        // symbols from the dylib.
        let src = &codegen_results.crate_info.used_crate_source[&cnum];
        match data[cnum.as_usize() - 1] {
            _ if codegen_results.crate_info.profiler_runtime == Some(cnum) => {
                add_static_crate::<B>(cmd, sess, codegen_results, tmpdir, crate_type, cnum);
            }
            // compiler-builtins are always placed last to ensure that they're
            // linked correctly.
            _ if codegen_results.crate_info.compiler_builtins == Some(cnum) => {
                assert!(compiler_builtins.is_none());
                compiler_builtins = Some(cnum);
            }
            Linkage::NotLinked | Linkage::IncludedFromDylib => {}
            Linkage::Static => {
                add_static_crate::<B>(cmd, sess, codegen_results, tmpdir, crate_type, cnum);
            }
            Linkage::Dynamic => add_dynamic_crate(cmd, sess, &src.dylib.as_ref().unwrap().0),
        }

        if group_end == Some(cnum) {
            cmd.group_end();
        }
    }

    // compiler-builtins are always placed last to ensure that they're
    // linked correctly.
    // We must always link the `compiler_builtins` crate statically. Even if it
    // was already "included" in a dylib (e.g., `libstd` when `-C prefer-dynamic`
    // is used)
    if let Some(cnum) = compiler_builtins {
        add_static_crate::<B>(cmd, sess, codegen_results, tmpdir, crate_type, cnum);
    }

    // Converts a library file-stem into a cc -l argument
    fn unlib<'a>(config: &config::Config, stem: &'a str) -> &'a str {
        if stem.starts_with("lib") && !config.target.options.is_like_windows {
            &stem[3..]
        } else {
            stem
        }
    }

    // Adds the static "rlib" versions of all crates to the command line.
    // There's a bit of magic which happens here specifically related to LTO and
    // dynamic libraries. Specifically:
    //
    // * For LTO, we remove upstream object files.
    // * For dylibs we remove metadata and bytecode from upstream rlibs
    //
    // When performing LTO, almost(*) all of the bytecode from the upstream
    // libraries has already been included in our object file output. As a
    // result we need to remove the object files in the upstream libraries so
    // the linker doesn't try to include them twice (or whine about duplicate
    // symbols). We must continue to include the rest of the rlib, however, as
    // it may contain static native libraries which must be linked in.
    //
    // (*) Crates marked with `#![no_builtins]` don't participate in LTO and
    // their bytecode wasn't included. The object files in those libraries must
    // still be passed to the linker.
    //
    // When making a dynamic library, linkers by default don't include any
    // object files in an archive if they're not necessary to resolve the link.
    // We basically want to convert the archive (rlib) to a dylib, though, so we
    // *do* want everything included in the output, regardless of whether the
    // linker thinks it's needed or not. As a result we must use the
    // --whole-archive option (or the platform equivalent). When using this
    // option the linker will fail if there are non-objects in the archive (such
    // as our own metadata and/or bytecode). All in all, for rlibs to be
    // entirely included in dylibs, we need to remove all non-object files.
    //
    // Note, however, that if we're not doing LTO or we're not producing a dylib
    // (aka we're making an executable), we can just pass the rlib blindly to
    // the linker (fast) because it's fine if it's not actually included as
    // we're at the end of the dependency chain.
    fn add_static_crate<'a, B: ArchiveBuilder<'a>>(
        cmd: &mut dyn Linker,
        sess: &'a Session,
        codegen_results: &CodegenResults,
        tmpdir: &Path,
        crate_type: config::CrateType,
        cnum: CrateNum,
    ) {
        let src = &codegen_results.crate_info.used_crate_source[&cnum];
        let cratepath = &src.rlib.as_ref().unwrap().0;

        // See the comment above in `link_staticlib` and `link_rlib` for why if
        // there's a static library that's not relevant we skip all object
        // files.
        let native_libs = &codegen_results.crate_info.native_libraries[&cnum];
        let skip_native = native_libs
            .iter()
            .any(|lib| lib.kind == NativeLibraryKind::NativeStatic && !relevant_lib(sess, lib));

        if (!are_upstream_rust_objects_already_included(sess)
            || ignored_for_lto(sess, &codegen_results.crate_info, cnum))
            && crate_type != config::CrateType::Dylib
            && !skip_native
        {
            cmd.link_rlib(&fix_windows_verbatim_for_gcc(cratepath));
            return;
        }

        let dst = tmpdir.join(cratepath.file_name().unwrap());
        let name = cratepath.file_name().unwrap().to_str().unwrap();
        let name = &name[3..name.len() - 5]; // chop off lib/.rlib

        sess.prof.generic_activity_with_arg("link_altering_rlib", name).run(|| {
            let mut archive = <B as ArchiveBuilder>::new(sess, &dst, Some(cratepath));
            archive.update_symbols();

            let mut any_objects = false;
            for f in archive.src_files() {
                if f.ends_with(RLIB_BYTECODE_EXTENSION) || f == METADATA_FILENAME {
                    archive.remove_file(&f);
                    continue;
                }

                let canonical = f.replace("-", "_");
                let canonical_name = name.replace("-", "_");

                let is_rust_object =
                    canonical.starts_with(&canonical_name) && looks_like_rust_object_file(&f);

                // If we've been requested to skip all native object files
                // (those not generated by the rust compiler) then we can skip
                // this file. See above for why we may want to do this.
                let skip_because_cfg_say_so = skip_native && !is_rust_object;

                // If we're performing LTO and this is a rust-generated object
                // file, then we don't need the object file as it's part of the
                // LTO module. Note that `#![no_builtins]` is excluded from LTO,
                // though, so we let that object file slide.
                let skip_because_lto = are_upstream_rust_objects_already_included(sess)
                    && is_rust_object
                    && (sess.target.target.options.no_builtins
                        || !codegen_results.crate_info.is_no_builtins.contains(&cnum));

                if skip_because_cfg_say_so || skip_because_lto {
                    archive.remove_file(&f);
                } else {
                    any_objects = true;
                }
            }

            if !any_objects {
                return;
            }
            archive.build();

            // If we're creating a dylib, then we need to include the
            // whole of each object in our archive into that artifact. This is
            // because a `dylib` can be reused as an intermediate artifact.
            //
            // Note, though, that we don't want to include the whole of a
            // compiler-builtins crate (e.g., compiler-rt) because it'll get
            // repeatedly linked anyway.
            if crate_type == config::CrateType::Dylib
                && codegen_results.crate_info.compiler_builtins != Some(cnum)
            {
                cmd.link_whole_rlib(&fix_windows_verbatim_for_gcc(&dst));
            } else {
                cmd.link_rlib(&fix_windows_verbatim_for_gcc(&dst));
            }
        });
    }

    // Same thing as above, but for dynamic crates instead of static crates.
    fn add_dynamic_crate(cmd: &mut dyn Linker, sess: &Session, cratepath: &Path) {
        // Just need to tell the linker about where the library lives and
        // what its name is
        let parent = cratepath.parent();
        if let Some(dir) = parent {
            cmd.include_path(&fix_windows_verbatim_for_gcc(dir));
        }
        let filestem = cratepath.file_stem().unwrap().to_str().unwrap();
        cmd.link_rust_dylib(
            Symbol::intern(&unlib(&sess.target, filestem)),
            parent.unwrap_or(Path::new("")),
        );
    }
}

// Link in all of our upstream crates' native dependencies. Remember that
// all of these upstream native dependencies are all non-static
// dependencies. We've got two cases then:
//
// 1. The upstream crate is an rlib. In this case we *must* link in the
// native dependency because the rlib is just an archive.
//
// 2. The upstream crate is a dylib. In order to use the dylib, we have to
// have the dependency present on the system somewhere. Thus, we don't
// gain a whole lot from not linking in the dynamic dependency to this
// crate as well.
//
// The use case for this is a little subtle. In theory the native
// dependencies of a crate are purely an implementation detail of the crate
// itself, but the problem arises with generic and inlined functions. If a
// generic function calls a native function, then the generic function must
// be instantiated in the target crate, meaning that the native symbol must
// also be resolved in the target crate.
pub fn add_upstream_native_libraries(
    cmd: &mut dyn Linker,
    sess: &Session,
    codegen_results: &CodegenResults,
    crate_type: config::CrateType,
) {
    // Be sure to use a topological sorting of crates because there may be
    // interdependencies between native libraries. When passing -nodefaultlibs,
    // for example, almost all native libraries depend on libc, so we have to
    // make sure that's all the way at the right (liblibc is near the base of
    // the dependency chain).
    //
    // This passes RequireStatic, but the actual requirement doesn't matter,
    // we're just getting an ordering of crate numbers, we're not worried about
    // the paths.
    let (_, data) = codegen_results
        .crate_info
        .dependency_formats
        .iter()
        .find(|(ty, _)| *ty == crate_type)
        .expect("failed to find crate type in dependency format list");

    let crates = &codegen_results.crate_info.used_crates_static;
    for &(cnum, _) in crates {
        for lib in codegen_results.crate_info.native_libraries[&cnum].iter() {
            let name = match lib.name {
                Some(l) => l,
                None => continue,
            };
            if !relevant_lib(sess, &lib) {
                continue;
            }
            match lib.kind {
                NativeLibraryKind::NativeUnknown => cmd.link_dylib(name),
                NativeLibraryKind::NativeFramework => cmd.link_framework(name),
                NativeLibraryKind::NativeStaticNobundle => {
                    // Link "static-nobundle" native libs only if the crate they originate from
                    // is being linked statically to the current crate.  If it's linked dynamically
                    // or is an rlib already included via some other dylib crate, the symbols from
                    // native libs will have already been included in that dylib.
                    if data[cnum.as_usize() - 1] == Linkage::Static {
                        cmd.link_staticlib(name)
                    }
                }
                // ignore statically included native libraries here as we've
                // already included them when we included the rust library
                // previously
                NativeLibraryKind::NativeStatic => {}
                NativeLibraryKind::NativeRawDylib => {
                    // FIXME(#58713): Proper handling for raw dylibs.
                    bug!("raw_dylib feature not yet implemented");
                }
            }
        }
    }
}

pub fn relevant_lib(sess: &Session, lib: &NativeLibrary) -> bool {
    match lib.cfg {
        Some(ref cfg) => rustc_attr::cfg_matches(cfg, &sess.parse_sess, None),
        None => true,
    }
}

pub fn are_upstream_rust_objects_already_included(sess: &Session) -> bool {
    match sess.lto() {
        config::Lto::Fat => true,
        config::Lto::Thin => {
            // If we defer LTO to the linker, we haven't run LTO ourselves, so
            // any upstream object files have not been copied yet.
            !sess.opts.cg.linker_plugin_lto.enabled()
        }
        config::Lto::No | config::Lto::ThinLocal => false,
    }
}

fn is_pic(sess: &Session) -> bool {
    let reloc_model_arg = match sess.opts.cg.relocation_model {
        Some(ref s) => &s[..],
        None => &sess.target.target.options.relocation_model[..],
    };

    reloc_model_arg == "pic"
}