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
// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use super::archive::{ArchiveBuilder, ArchiveConfig};
use super::linker::Linker;
use super::rpath::RPathConfig;
use super::rpath;
use super::msvc;
use session::config;
use session::config::NoDebugInfo;
use session::config::{OutputFilenames, Input, OutputType};
use session::filesearch;
use session::search_paths::PathKind;
use session::Session;
use middle::cstore::{self, LinkMeta, NativeLibrary, LibSource};
use middle::cstore::{LinkagePreference, NativeLibraryKind};
use middle::dependency_format::Linkage;
use CrateTranslation;
use util::common::time;
use util::fs::fix_windows_verbatim_for_gcc;
use rustc::dep_graph::DepNode;
use rustc::hir::def_id::CrateNum;
use rustc::hir::svh::Svh;
use rustc_back::tempdir::TempDir;
use rustc_back::PanicStrategy;
use rustc_incremental::IncrementalHashesMap;
use context::get_reloc_model;
use llvm;

use std::ascii;
use std::char;
use std::env;
use std::ffi::OsString;
use std::fs;
use std::io::{self, Read, Write};
use std::mem;
use std::path::{Path, PathBuf};
use std::process::Command;
use std::str;
use flate;
use syntax::ast;
use syntax::attr;
use syntax::symbol::Symbol;
use syntax_pos::Span;

/// The LLVM module name containing crate-metadata. This includes a `.` on
/// purpose, so it cannot clash with the name of a user-defined module.
pub const METADATA_MODULE_NAME: &'static str = "crate.metadata";
/// The name of the crate-metadata object file the compiler generates. Must
/// match up with `METADATA_MODULE_NAME`.
pub const METADATA_OBJ_NAME: &'static str = "crate.metadata.o";

// RLIB LLVM-BYTECODE OBJECT LAYOUT
// Version 1
// Bytes    Data
// 0..10    "RUST_OBJECT" encoded in ASCII
// 11..14   format version as little-endian u32
// 15..22   size in bytes of deflate compressed LLVM bitcode as
//          little-endian u64
// 23..     compressed LLVM bitcode

// This is the "magic number" expected at the beginning of a LLVM bytecode
// object in an rlib.
pub const RLIB_BYTECODE_OBJECT_MAGIC: &'static [u8] = b"RUST_OBJECT";

// The version number this compiler will write to bytecode objects in rlibs
pub const RLIB_BYTECODE_OBJECT_VERSION: u32 = 1;

// The offset in bytes the bytecode object format version number can be found at
pub const RLIB_BYTECODE_OBJECT_VERSION_OFFSET: usize = 11;

// The offset in bytes the size of the compressed bytecode can be found at in
// format version 1
pub const RLIB_BYTECODE_OBJECT_V1_DATASIZE_OFFSET: usize =
    RLIB_BYTECODE_OBJECT_VERSION_OFFSET + 4;

// The offset in bytes the compressed LLVM bytecode can be found at in format
// version 1
pub const RLIB_BYTECODE_OBJECT_V1_DATA_OFFSET: usize =
    RLIB_BYTECODE_OBJECT_V1_DATASIZE_OFFSET + 8;


pub fn find_crate_name(sess: Option<&Session>,
                       attrs: &[ast::Attribute],
                       input: &Input) -> String {
    let validate = |s: String, span: Option<Span>| {
        cstore::validate_crate_name(sess, &s[..], span);
        s
    };

    // Look in attributes 100% of the time to make sure the attribute is marked
    // as used. After doing this, however, we still prioritize a crate name from
    // the command line over one found in the #[crate_name] attribute. If we
    // find both we ensure that they're the same later on as well.
    let attr_crate_name = attrs.iter().find(|at| at.check_name("crate_name"))
                               .and_then(|at| at.value_str().map(|s| (at, s)));

    if let Some(sess) = sess {
        if let Some(ref s) = sess.opts.crate_name {
            if let Some((attr, name)) = attr_crate_name {
                if name != &**s {
                    let msg = format!("--crate-name and #[crate_name] are \
                                       required to match, but `{}` != `{}`",
                                      s, name);
                    sess.span_err(attr.span, &msg[..]);
                }
            }
            return validate(s.clone(), None);
        }
    }

    if let Some((attr, s)) = attr_crate_name {
        return validate(s.to_string(), Some(attr.span));
    }
    if let Input::File(ref path) = *input {
        if let Some(s) = path.file_stem().and_then(|s| s.to_str()) {
            if s.starts_with("-") {
                let msg = format!("crate names cannot start with a `-`, but \
                                   `{}` has a leading hyphen", s);
                if let Some(sess) = sess {
                    sess.err(&msg);
                }
            } else {
                return validate(s.replace("-", "_"), None);
            }
        }
    }

    "rust_out".to_string()
}

pub fn build_link_meta(incremental_hashes_map: &IncrementalHashesMap,
                       name: &str)
                       -> LinkMeta {
    let r = LinkMeta {
        crate_name: Symbol::intern(name),
        crate_hash: Svh::new(incremental_hashes_map[&DepNode::Krate].to_smaller_hash()),
    };
    info!("{:?}", r);
    return r;
}

// The third parameter is for an extra path to add to PATH for MSVC
// cross linkers for host toolchain DLL dependencies
pub fn get_linker(sess: &Session) -> (String, Command, Option<PathBuf>) {
    if let Some(ref linker) = sess.opts.cg.linker {
        (linker.clone(), Command::new(linker), None)
    } else if sess.target.target.options.is_like_msvc {
        let (cmd, host) = msvc::link_exe_cmd(sess);
        ("link.exe".to_string(), cmd, host)
    } else {
        (sess.target.target.options.linker.clone(),
         Command::new(&sess.target.target.options.linker), None)
    }
}

pub fn get_ar_prog(sess: &Session) -> String {
    sess.opts.cg.ar.clone().unwrap_or_else(|| {
        sess.target.target.options.ar.clone()
    })
}

fn command_path(sess: &Session, extra: Option<PathBuf>) -> OsString {
    // 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();
    if let Some(path) = env::var_os("PATH") {
        new_path.extend(env::split_paths(&path));
    }
    new_path.extend(extra);
    env::join_paths(new_path).unwrap()
}

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

/// Perform the linkage portion of the compilation phase. This will generate all
/// of the requested outputs for this compilation session.
pub fn link_binary(sess: &Session,
                   trans: &CrateTranslation,
                   outputs: &OutputFilenames,
                   crate_name: &str) -> Vec<PathBuf> {
    let _task = sess.dep_graph.in_task(DepNode::LinkBinary);

    let mut out_filenames = Vec::new();
    for &crate_type in sess.crate_types.borrow().iter() {
        // Ignore executable crates if we have -Z no-trans, as they will error.
        if (sess.opts.debugging_opts.no_trans ||
            !sess.opts.output_types.should_trans()) &&
           crate_type == config::CrateTypeExecutable {
            continue;
        }

        if invalid_output_for_target(sess, crate_type) {
           bug!("invalid output type `{:?}` for target os `{}`",
                crate_type, sess.opts.target_triple);
        }
        let mut out_files = link_binary_output(sess, trans, crate_type, outputs, crate_name);
        out_filenames.append(&mut out_files);
    }

    // Remove the temporary object file and metadata if we aren't saving temps
    if !sess.opts.cg.save_temps {
        if sess.opts.output_types.should_trans() {
            for obj in object_filenames(trans, outputs) {
                remove(sess, &obj);
            }
        }
        remove(sess, &outputs.with_extension(METADATA_OBJ_NAME));
    }

    out_filenames
}


/// Returns default crate type for target
///
/// Default crate type is used when crate type isn't provided neither
/// through cmd line arguments nor through crate attributes
///
/// It is CrateTypeExecutable for all platforms but iOS as there is no
/// way to run iOS binaries anyway without jailbreaking and
/// interaction with Rust code through static library is the only
/// option for now
pub fn default_output_for_target(sess: &Session) -> config::CrateType {
    if !sess.target.target.options.executables {
        config::CrateTypeStaticlib
    } else {
        config::CrateTypeExecutable
    }
}

/// Checks if target supports crate_type as output
pub fn invalid_output_for_target(sess: &Session,
                                 crate_type: config::CrateType) -> bool {
    match (sess.target.target.options.dynamic_linking,
           sess.target.target.options.executables, crate_type) {
        (false, _, config::CrateTypeCdylib) |
        (false, _, config::CrateTypeProcMacro) |
        (false, _, config::CrateTypeDylib) => true,
        (_, false, config::CrateTypeExecutable) => true,
        _ => false
    }
}

fn is_writeable(p: &Path) -> bool {
    match p.metadata() {
        Err(..) => true,
        Ok(m) => !m.permissions().readonly()
    }
}

fn filename_for_metadata(sess: &Session, crate_name: &str, outputs: &OutputFilenames) -> PathBuf {
    let out_filename = outputs.single_output_file.clone()
        .unwrap_or(outputs
            .out_directory
            .join(&format!("lib{}{}.rmeta", crate_name, sess.opts.cg.extra_filename)));
    check_file_is_writeable(&out_filename, sess);
    out_filename
}

pub fn filename_for_input(sess: &Session,
                          crate_type: config::CrateType,
                          crate_name: &str,
                          outputs: &OutputFilenames) -> PathBuf {
    let libname = format!("{}{}", crate_name, sess.opts.cg.extra_filename);

    match crate_type {
        config::CrateTypeRlib => {
            outputs.out_directory.join(&format!("lib{}.rlib", libname))
        }
        config::CrateTypeCdylib |
        config::CrateTypeProcMacro |
        config::CrateTypeDylib => {
            let (prefix, suffix) = (&sess.target.target.options.dll_prefix,
                                    &sess.target.target.options.dll_suffix);
            outputs.out_directory.join(&format!("{}{}{}", prefix, libname,
                                                suffix))
        }
        config::CrateTypeStaticlib => {
            let (prefix, suffix) = (&sess.target.target.options.staticlib_prefix,
                                    &sess.target.target.options.staticlib_suffix);
            outputs.out_directory.join(&format!("{}{}{}", prefix, libname,
                                                suffix))
        }
        config::CrateTypeExecutable => {
            let suffix = &sess.target.target.options.exe_suffix;
            let out_filename = outputs.path(OutputType::Exe);
            if suffix.is_empty() {
                out_filename.to_path_buf()
            } else {
                out_filename.with_extension(&suffix[1..])
            }
        }
    }
}

pub fn each_linked_rlib(sess: &Session,
                        f: &mut FnMut(CrateNum, &Path)) {
    let crates = sess.cstore.used_crates(LinkagePreference::RequireStatic).into_iter();
    let fmts = sess.dependency_formats.borrow();
    let fmts = fmts.get(&config::CrateTypeExecutable)
                   .or_else(|| fmts.get(&config::CrateTypeStaticlib))
                   .or_else(|| fmts.get(&config::CrateTypeCdylib))
                   .or_else(|| fmts.get(&config::CrateTypeProcMacro));
    let fmts = fmts.unwrap_or_else(|| {
        bug!("could not find formats for rlibs");
    });
    for (cnum, path) in crates {
        match fmts[cnum.as_usize() - 1] {
            Linkage::NotLinked | Linkage::IncludedFromDylib => continue,
            _ => {}
        }
        let name = sess.cstore.crate_name(cnum).clone();
        let path = match path {
            LibSource::Some(p) => p,
            LibSource::MetadataOnly => {
                sess.fatal(&format!("could not find rlib for: `{}`, found rmeta (metadata) file",
                                    name));
            }
            LibSource::None => {
                sess.fatal(&format!("could not find rlib for: `{}`", name));
            }
        };
        f(cnum, &path);
    }
}

fn out_filename(sess: &Session,
                crate_type: config::CrateType,
                outputs: &OutputFilenames,
                crate_name: &str)
                -> PathBuf {
    let default_filename = filename_for_input(sess, crate_type, crate_name, outputs);
    let out_filename = outputs.outputs.get(&OutputType::Exe)
                              .and_then(|s| s.to_owned())
                              .or_else(|| outputs.single_output_file.clone())
                              .unwrap_or(default_filename);

    check_file_is_writeable(&out_filename, sess);

    out_filename
}

// Make sure files are writeable.  Mac, FreeBSD, and Windows system linkers
// check this already -- however, the Linux linker will happily overwrite a
// read-only file.  We should be consistent.
fn check_file_is_writeable(file: &Path, sess: &Session) {
    if !is_writeable(file) {
        sess.fatal(&format!("output file {} is not writeable -- check its \
                            permissions", file.display()));
    }
}

fn link_binary_output(sess: &Session,
                      trans: &CrateTranslation,
                      crate_type: config::CrateType,
                      outputs: &OutputFilenames,
                      crate_name: &str) -> Vec<PathBuf> {
    let objects = object_filenames(trans, outputs);

    for file in &objects {
        check_file_is_writeable(file, sess);
    }

    let tmpdir = match TempDir::new("rustc") {
        Ok(tmpdir) => tmpdir,
        Err(err) => sess.fatal(&format!("couldn't create a temp dir: {}", err)),
    };

    let mut out_filenames = vec![];

    if outputs.outputs.contains_key(&OutputType::Metadata) {
        let out_filename = filename_for_metadata(sess, crate_name, outputs);
        emit_metadata(sess, trans, &out_filename);
        out_filenames.push(out_filename);
    }

    if outputs.outputs.should_trans() {
        let out_filename = out_filename(sess, crate_type, outputs, crate_name);
        match crate_type {
            config::CrateTypeRlib => {
                link_rlib(sess, Some(trans), &objects, &out_filename,
                          tmpdir.path()).build();
            }
            config::CrateTypeStaticlib => {
                link_staticlib(sess, &objects, &out_filename, tmpdir.path());
            }
            _ => {
                link_natively(sess, crate_type, &objects, &out_filename, trans,
                              outputs, tmpdir.path());
            }
        }
        out_filenames.push(out_filename);
    }

    out_filenames
}

fn object_filenames(trans: &CrateTranslation,
                    outputs: &OutputFilenames)
                    -> Vec<PathBuf> {
    trans.modules.iter().map(|module| {
        outputs.temp_path(OutputType::Object, Some(&module.name[..]))
    }).collect()
}

fn archive_search_paths(sess: &Session) -> Vec<PathBuf> {
    let mut search = Vec::new();
    sess.target_filesearch(PathKind::Native).for_each_lib_search_path(|path, _| {
        search.push(path.to_path_buf());
    });
    return search;
}

fn archive_config<'a>(sess: &'a Session,
                      output: &Path,
                      input: Option<&Path>) -> ArchiveConfig<'a> {
    ArchiveConfig {
        sess: sess,
        dst: output.to_path_buf(),
        src: input.map(|p| p.to_path_buf()),
        lib_search_paths: archive_search_paths(sess),
        ar_prog: get_ar_prog(sess),
        command_path: command_path(sess, None),
    }
}

fn emit_metadata<'a>(sess: &'a Session, trans: &CrateTranslation, out_filename: &Path) {
    let result = fs::File::create(out_filename).and_then(|mut f| f.write_all(&trans.metadata));
    if let Err(e) = result {
        sess.fatal(&format!("failed to write {}: {}", out_filename.display(), e));
    }
}

// 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>(sess: &'a Session,
                 trans: Option<&CrateTranslation>, // None == no metadata/bytecode
                 objects: &[PathBuf],
                 out_filename: &Path,
                 tmpdir: &Path) -> ArchiveBuilder<'a> {
    info!("preparing rlib from {:?} to {:?}", objects, out_filename);
    let mut ab = ArchiveBuilder::new(archive_config(sess, out_filename, None));

    for obj in objects {
        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 sess.cstore.used_libraries() {
        match lib.kind {
            NativeLibraryKind::NativeStatic => {}
            NativeLibraryKind::NativeStaticNobundle |
            NativeLibraryKind::NativeFramework |
            NativeLibraryKind::NativeUnknown => continue,
        }
        ab.add_native_library(&lib.name.as_str());
    }

    // 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 trans {
        Some(trans) => {
            // Instead of putting the metadata in an object file section, rlibs
            // contain the metadata in a separate file. We use a temp directory
            // here so concurrent builds in the same directory don't try to use
            // the same filename for metadata (stomping over one another)
            let metadata = tmpdir.join(sess.cstore.metadata_filename());
            emit_metadata(sess, trans, &metadata);
            ab.add_file(&metadata);

            // For LTO purposes, the bytecode of this library is also inserted
            // into the archive.  If codegen_units > 1, we insert each of the
            // bitcode files.
            for obj in objects {
                // Note that we make sure that the bytecode filename in the
                // archive is never exactly 16 bytes long by adding a 16 byte
                // extension to it. This is to work around a bug in LLDB that
                // would cause it to crash if the name of a file in an archive
                // was exactly 16 bytes.
                let bc_filename = obj.with_extension("bc");
                let bc_deflated_filename = tmpdir.join({
                    obj.with_extension("bytecode.deflate").file_name().unwrap()
                });

                let mut bc_data = Vec::new();
                match fs::File::open(&bc_filename).and_then(|mut f| {
                    f.read_to_end(&mut bc_data)
                }) {
                    Ok(..) => {}
                    Err(e) => sess.fatal(&format!("failed to read bytecode: {}",
                                                 e))
                }

                let bc_data_deflated = flate::deflate_bytes(&bc_data[..]);

                let mut bc_file_deflated = match fs::File::create(&bc_deflated_filename) {
                    Ok(file) => file,
                    Err(e) => {
                        sess.fatal(&format!("failed to create compressed \
                                             bytecode file: {}", e))
                    }
                };

                match write_rlib_bytecode_object_v1(&mut bc_file_deflated,
                                                    &bc_data_deflated) {
                    Ok(()) => {}
                    Err(e) => {
                        sess.fatal(&format!("failed to write compressed \
                                             bytecode: {}", e));
                    }
                };

                ab.add_file(&bc_deflated_filename);

                // See the bottom of back::write::run_passes for an explanation
                // of when we do and don't keep .#module-name#.bc files around.
                let user_wants_numbered_bitcode =
                        sess.opts.output_types.contains_key(&OutputType::Bitcode) &&
                        sess.opts.cg.codegen_units > 1;
                if !sess.opts.cg.save_temps && !user_wants_numbered_bitcode {
                    remove(sess, &bc_filename);
                }
            }

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

        None => {}
    }

    ab
}

fn write_rlib_bytecode_object_v1(writer: &mut Write,
                                 bc_data_deflated: &[u8]) -> io::Result<()> {
    let bc_data_deflated_size: u64 = bc_data_deflated.len() as u64;

    writer.write_all(RLIB_BYTECODE_OBJECT_MAGIC)?;
    writer.write_all(&[1, 0, 0, 0])?;
    writer.write_all(&[
        (bc_data_deflated_size >>  0) as u8,
        (bc_data_deflated_size >>  8) as u8,
        (bc_data_deflated_size >> 16) as u8,
        (bc_data_deflated_size >> 24) as u8,
        (bc_data_deflated_size >> 32) as u8,
        (bc_data_deflated_size >> 40) as u8,
        (bc_data_deflated_size >> 48) as u8,
        (bc_data_deflated_size >> 56) as u8,
    ])?;
    writer.write_all(&bc_data_deflated)?;

    let number_of_bytes_written_so_far =
        RLIB_BYTECODE_OBJECT_MAGIC.len() +                // magic id
        mem::size_of_val(&RLIB_BYTECODE_OBJECT_VERSION) + // version
        mem::size_of_val(&bc_data_deflated_size) +        // data size field
        bc_data_deflated_size as usize;                    // actual data

    // If the number of bytes written to the object so far is odd, add a
    // padding byte to make it even. This works around a crash bug in LLDB
    // (see issue #15950)
    if number_of_bytes_written_so_far % 2 == 1 {
        writer.write_all(&[0])?;
    }

    return Ok(());
}

// 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(sess: &Session, objects: &[PathBuf], out_filename: &Path,
                  tempdir: &Path) {
    let mut ab = link_rlib(sess, None, objects, out_filename, tempdir);
    let mut all_native_libs = vec![];

    each_linked_rlib(sess, &mut |cnum, path| {
        let name = sess.cstore.crate_name(cnum);
        let native_libs = sess.cstore.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(), sess.lto(), skip_object_files).unwrap();

        all_native_libs.extend(sess.cstore.native_libraries(cnum));
    });

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

    if !all_native_libs.is_empty() {
        sess.note_without_error("link against the following native artifacts when linking against \
                                 this static library");
        sess.note_without_error("the order and any duplication can be significant on some \
                                 platforms, and so may need to be preserved");
    }

    for lib in all_native_libs.iter().filter(|l| relevant_lib(sess, l)) {
        let name = match lib.kind {
            NativeLibraryKind::NativeStaticNobundle |
            NativeLibraryKind::NativeUnknown => "library",
            NativeLibraryKind::NativeFramework => "framework",
            // These are included, no need to print them
            NativeLibraryKind::NativeStatic => continue,
        };
        sess.note_without_error(&format!("{}: {}", name, lib.name));
    }
}

// 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(sess: &Session,
                 crate_type: config::CrateType,
                 objects: &[PathBuf],
                 out_filename: &Path,
                 trans: &CrateTranslation,
                 outputs: &OutputFilenames,
                 tmpdir: &Path) {
    info!("preparing {:?} from {:?} to {:?}", crate_type, objects, out_filename);

    // The invocations of cc share some flags across platforms
    let (pname, mut cmd, extra) = get_linker(sess);
    cmd.env("PATH", command_path(sess, extra));

    let root = sess.target_filesearch(PathKind::Native).get_lib_path();
    cmd.args(&sess.target.target.options.pre_link_args);

    let pre_link_objects = if crate_type == config::CrateTypeExecutable {
        &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(root.join(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 = trans.linker_info.to_linker(&mut cmd, &sess);
        link_args(&mut *linker, sess, crate_type, tmpdir,
                  objects, out_filename, outputs, trans);
    }
    cmd.args(&sess.target.target.options.late_link_args);
    for obj in &sess.target.target.options.post_link_objects {
        cmd.arg(root.join(obj));
    }
    cmd.args(&sess.target.target.options.post_link_args);

    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
    //
    // Note that there'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 OSX'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...
    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 = time(sess.time_passes(), "running linker", || cmd.output());
        if !retry_on_segfault || i > 3 {
            break
        }
        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);
        let msg = "clang: error: unable to execute command: \
                   Segmentation fault: 11";
        if !out.contains(msg) {
            break
        }

        sess.struct_warn("looks like the linker segfaulted when we tried to \
                          call it, automatically retrying again")
            .note(&format!("{:?}", cmd))
            .note(&out)
            .emit();
    }

    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(|b| char::from_u32(b as u32).unwrap()));
                        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,
                                         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) => {
            sess.struct_err(&format!("could not exec the linker `{}`: {}", pname, e))
                .note(&format!("{:?}", &cmd))
                .emit();
            if sess.target.target.options.is_like_msvc && e.kind() == io::ErrorKind::NotFound {
                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 or VS 2015 was installed \
                    with the Visual C++ option");
            }
            sess.abort_if_errors();
        }
    }


    // On OSX, debuggers need this utility to get run to do some munging of
    // the symbols
    if sess.target.target.options.is_like_osx && sess.opts.debuginfo != NoDebugInfo {
        match Command::new("dsymutil").arg(out_filename).output() {
            Ok(..) => {}
            Err(e) => sess.fatal(&format!("failed to run dsymutil: {}", e)),
        }
    }
}

fn link_args(cmd: &mut Linker,
             sess: &Session,
             crate_type: config::CrateType,
             tmpdir: &Path,
             objects: &[PathBuf],
             out_filename: &Path,
             outputs: &OutputFilenames,
             trans: &CrateTranslation) {

    // 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;

    cmd.include_path(&fix_windows_verbatim_for_gcc(&lib_path));
    for obj in objects {
        cmd.add_object(obj);
    }
    cmd.output_filename(out_filename);

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

    // If we're building a dynamic library then some platforms need to make sure
    // that all symbols are exported correctly from the dynamic library.
    if crate_type != config::CrateTypeExecutable ||
       sess.target.target.options.is_like_emscripten {
        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::CrateTypeDylib ||
       crate_type == config::CrateTypeProcMacro {
        cmd.add_object(&outputs.with_extension(METADATA_OBJ_NAME));
    }

    // 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::CrateTypeDylib;
        cmd.gc_sections(keep_metadata);
    }

    let used_link_args = sess.cstore.used_link_args();

    if crate_type == config::CrateTypeExecutable &&
       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 get_reloc_model(sess) == llvm::RelocMode::PIC
            && !args.any(|x| *x == "-static") {
            cmd.position_independent_executable();
        }
    }

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

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

    // We want to prevent the compiler from accidentally leaking in any system
    // libraries, so we explicitly ask gcc 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.
    if 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);
    add_upstream_rust_crates(cmd, sess, crate_type, tmpdir);
    add_upstream_native_libraries(cmd, sess, crate_type);

    // # Telling the linker what we're doing

    if crate_type != config::CrateTypeExecutable {
        cmd.build_dylib(out_filename);
    }

    // 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 sysroot = sess.sysroot();
        let target_triple = &sess.opts.target_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(sysroot, target_triple);
            let mut path = PathBuf::from(install_prefix);
            path.push(&tlib);

            path
        };
        let mut rpath_config = RPathConfig {
            used_crates: sess.cstore.used_crates(LinkagePreference::RequireDynamic),
            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));
    }

    if (crate_type == config::CrateTypeDylib || crate_type == config::CrateTypeCdylib) && t.options.linker_is_gnu {
        let filename = String::from(out_filename.file_name().unwrap().to_str().unwrap());
        let soname = [String::from("-Wl,-soname=") + &filename];
        cmd.args(&soname);
    }

    // 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.
fn add_local_native_libraries(cmd: &mut Linker, sess: &Session) {
    sess.target_filesearch(PathKind::All).for_each_lib_search_path(|path, k| {
        match k {
            PathKind::Framework => { cmd.framework_path(path); }
            _ => { cmd.include_path(&fix_windows_verbatim_for_gcc(path)); }
        }
    });

    let pair = sess.cstore.used_libraries().into_iter().filter(|l| {
        relevant_lib(sess, l)
    }).partition(|lib| {
        lib.kind == NativeLibraryKind::NativeStatic
    });
    let (staticlibs, others): (Vec<_>, Vec<_>) = pair;

    // Some platforms take hints about whether a library is static or dynamic.
    // For those that support this, we ensure we pass the option if the library
    // was flagged "static" (most defaults are dynamic) to ensure that if
    // libfoo.a and libfoo.so both exist that the right one is chosen.
    cmd.hint_static();

    let search_path = archive_search_paths(sess);
    for l in staticlibs {
        // Here we explicitly ask that the entire archive is included into the
        // result artifact. For more details see #15460, but the gist is that
        // the linker will strip away any unused objects in the archive if we
        // don't otherwise explicitly reference them. This can occur for
        // libraries which are just providing bindings, libraries with generic
        // functions, etc.
        cmd.link_whole_staticlib(&l.name.as_str(), &search_path);
    }

    cmd.hint_dynamic();

    for lib in others {
        match lib.kind {
            NativeLibraryKind::NativeUnknown => cmd.link_dylib(&lib.name.as_str()),
            NativeLibraryKind::NativeFramework => cmd.link_framework(&lib.name.as_str()),
            NativeLibraryKind::NativeStaticNobundle => cmd.link_staticlib(&lib.name.as_str()),
            NativeLibraryKind::NativeStatic => bug!(),
        }
    }
}

// # 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(cmd: &mut Linker,
                            sess: &Session,
                            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 formats = sess.dependency_formats.borrow();
    let data = formats.get(&crate_type).unwrap();

    // Invoke get_used_crates to ensure that we get a topological sorting of
    // crates.
    let deps = sess.cstore.used_crates(LinkagePreference::RequireDynamic);

    let mut compiler_builtins = None;

    for &(cnum, _) in &deps {
        // 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 = sess.cstore.used_crate_source(cnum);
        match data[cnum.as_usize() - 1] {
            _ if sess.cstore.is_sanitizer_runtime(cnum) => {
                link_sanitizer_runtime(cmd, sess, tmpdir, cnum);
            }
            // compiler-builtins are always placed last to ensure that they're
            // linked correctly.
            _ if sess.cstore.is_compiler_builtins(cnum) => {
                assert!(compiler_builtins.is_none());
                compiler_builtins = Some(cnum);
            }
            Linkage::NotLinked |
            Linkage::IncludedFromDylib => {}
            Linkage::Static => {
                add_static_crate(cmd, sess, tmpdir, crate_type, cnum);
            }
            Linkage::Dynamic => {
                add_dynamic_crate(cmd, sess, &src.dylib.unwrap().0)
            }
        }
    }

    // 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(cmd, sess, 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
        }
    }

    // We must link the sanitizer runtime using -Wl,--whole-archive but since
    // it's packed in a .rlib, it contains stuff that are not objects that will
    // make the linker error. So we must remove those bits from the .rlib before
    // linking it.
    fn link_sanitizer_runtime(cmd: &mut Linker,
                              sess: &Session,
                              tmpdir: &Path,
                              cnum: CrateNum) {
        let src = sess.cstore.used_crate_source(cnum);
        let cratepath = &src.rlib.unwrap().0;
        let dst = tmpdir.join(cratepath.file_name().unwrap());
        let cfg = archive_config(sess, &dst, Some(cratepath));
        let mut archive = ArchiveBuilder::new(cfg);
        archive.update_symbols();

        for f in archive.src_files() {
            if f.ends_with("bytecode.deflate") ||
                f == sess.cstore.metadata_filename() {
                    archive.remove_file(&f);
                    continue
                }
        }

        archive.build();

        cmd.link_whole_rlib(&dst);
    }

    // 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(cmd: &mut Linker,
                        sess: &Session,
                        tmpdir: &Path,
                        crate_type: config::CrateType,
                        cnum: CrateNum) {
        let src = sess.cstore.used_crate_source(cnum);
        let cratepath = &src.rlib.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 = sess.cstore.native_libraries(cnum);
        let skip_native = native_libs.iter().any(|lib| {
            lib.kind == NativeLibraryKind::NativeStatic && !relevant_lib(sess, lib)
        });

        if !sess.lto() && crate_type != config::CrateTypeDylib && !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

        time(sess.time_passes(), &format!("altering {}.rlib", name), || {
            let cfg = archive_config(sess, &dst, Some(cratepath));
            let mut archive = ArchiveBuilder::new(cfg);
            archive.update_symbols();

            let mut any_objects = false;
            for f in archive.src_files() {
                if f.ends_with("bytecode.deflate") ||
                   f == sess.cstore.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) && {
                        let num = &f[name.len()..f.len() - 2];
                        num.len() > 0 && num[1..].parse::<u32>().is_ok()
                    };

                // 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 = sess.lto() && is_rust_object &&
                                        !sess.cstore.is_no_builtins(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::CrateTypeDylib &&
               !sess.cstore.is_compiler_builtins(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 Linker, sess: &Session, cratepath: &Path) {
        // If we're performing LTO, then it should have been previously required
        // that all upstream rust dependencies were available in an rlib format.
        assert!(!sess.lto());

        // 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(&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.
fn add_upstream_native_libraries(cmd: &mut Linker, sess: &Session, 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 formats = sess.dependency_formats.borrow();
    let data = formats.get(&crate_type).unwrap();

    let crates = sess.cstore.used_crates(LinkagePreference::RequireStatic);
    for (cnum, _) in crates {
        for lib in sess.cstore.native_libraries(cnum) {
            if !relevant_lib(sess, &lib) {
                continue
            }
            match lib.kind {
                NativeLibraryKind::NativeUnknown => cmd.link_dylib(&lib.name.as_str()),
                NativeLibraryKind::NativeFramework => cmd.link_framework(&lib.name.as_str()),
                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(&lib.name.as_str())
                    }
                },
                // ignore statically included native libraries here as we've
                // already included them when we included the rust library
                // previously
                NativeLibraryKind::NativeStatic => {}
            }
        }
    }
}

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