compiler/rustc_codegen_ssa/src/back/symbol_export.rs

   1 use std::collections::hash_map::Entry::*;
   2
   3 use rustc_ast::expand::allocator::ALLOCATOR_METHODS;
   4 use rustc_data_structures::fx::FxHashMap;
   5 use rustc_hir as hir;
   6 use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LocalDefId, LOCAL_CRATE};
   7 use rustc_hir::Node;
   8 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
   9 use rustc_middle::middle::exported_symbols::{
  10     metadata_symbol_name, ExportedSymbol, SymbolExportInfo, SymbolExportKind, SymbolExportLevel,
  11 };
  12 use rustc_middle::ty::query::{ExternProviders, Providers};
  13 use rustc_middle::ty::subst::{GenericArgKind, SubstsRef};
  14 use rustc_middle::ty::Instance;
  15 use rustc_middle::ty::{self, SymbolName, TyCtxt};
  16 use rustc_session::config::{CrateType, OomStrategy};
  17 use rustc_target::spec::SanitizerSet;
  18
  19 pub fn threshold(tcx: TyCtxt<'_>) -> SymbolExportLevel {
  20     crates_export_threshold(&tcx.sess.crate_types())
  21 }
  22
  23 fn crate_export_threshold(crate_type: CrateType) -> SymbolExportLevel {
  24     match crate_type {
  25         CrateType::Executable | CrateType::Staticlib | CrateType::ProcMacro | CrateType::Cdylib => {
  26             SymbolExportLevel::C
  27         }
  28         CrateType::Rlib | CrateType::Dylib => SymbolExportLevel::Rust,
  29     }
  30 }
  31
  32 pub fn crates_export_threshold(crate_types: &[CrateType]) -> SymbolExportLevel {
  33     if crate_types
  34         .iter()
  35         .any(|&crate_type| crate_export_threshold(crate_type) == SymbolExportLevel::Rust)
  36     {
  37         SymbolExportLevel::Rust
  38     } else {
  39         SymbolExportLevel::C
  40     }
  41 }
  42
  43 fn reachable_non_generics_provider(tcx: TyCtxt<'_>, cnum: CrateNum) -> DefIdMap<SymbolExportInfo> {
  44     assert_eq!(cnum, LOCAL_CRATE);
  45
  46     if !tcx.sess.opts.output_types.should_codegen() {
  47         return Default::default();
  48     }
  49
  50     // Check to see if this crate is a "special runtime crate". These
  51     // crates, implementation details of the standard library, typically
  52     // have a bunch of `pub extern` and `#[no_mangle]` functions as the
  53     // ABI between them. We don't want their symbols to have a `C`
  54     // export level, however, as they're just implementation details.
  55     // Down below we'll hardwire all of the symbols to the `Rust` export
  56     // level instead.
  57     let special_runtime_crate =
  58         tcx.is_panic_runtime(LOCAL_CRATE) || tcx.is_compiler_builtins(LOCAL_CRATE);
  59
  60     let mut reachable_non_generics: DefIdMap<_> = tcx
  61         .reachable_set(())
  62         .iter()
  63         .filter_map(|&def_id| {
  64             // We want to ignore some FFI functions that are not exposed from
  65             // this crate. Reachable FFI functions can be lumped into two
  66             // categories:
  67             //
  68             // 1. Those that are included statically via a static library
  69             // 2. Those included otherwise (e.g., dynamically or via a framework)
  70             //
  71             // Although our LLVM module is not literally emitting code for the
  72             // statically included symbols, it's an export of our library which
  73             // needs to be passed on to the linker and encoded in the metadata.
  74             //
  75             // As a result, if this id is an FFI item (foreign item) then we only
  76             // let it through if it's included statically.
  77             match tcx.hir().get_by_def_id(def_id) {
  78                 Node::ForeignItem(..) => {
  79                     tcx.native_library(def_id).map_or(false, |library| library.kind.is_statically_included()).then_some(def_id)
  80                 }
  81
  82                 // Only consider nodes that actually have exported symbols.
  83                 Node::Item(&hir::Item {
  84                     kind: hir::ItemKind::Static(..) | hir::ItemKind::Fn(..),
  85                     ..
  86                 })
  87                 | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(..), .. }) => {
  88                     let generics = tcx.generics_of(def_id);
  89                     if !generics.requires_monomorphization(tcx)
  90                         // Functions marked with #[inline] are codegened with "internal"
  91                         // linkage and are not exported unless marked with an extern
  92                         // indicator
  93                         && (!Instance::mono(tcx, def_id.to_def_id()).def.generates_cgu_internal_copy(tcx)
  94                             || tcx.codegen_fn_attrs(def_id.to_def_id()).contains_extern_indicator())
  95                     {
  96                         Some(def_id)
  97                     } else {
  98                         None
  99                     }
 100                 }
 101
 102                 _ => None,
 103             }
 104         })
 105         .map(|def_id| {
 106             // We won't link right if this symbol is stripped during LTO.
 107             let name = tcx.symbol_name(Instance::mono(tcx, def_id.to_def_id())).name;
 108             let used = name == "rust_eh_personality";
 109
 110             let export_level = if special_runtime_crate {
 111                 SymbolExportLevel::Rust
 112             } else {
 113                 symbol_export_level(tcx, def_id.to_def_id())
 114             };
 115             let codegen_attrs = tcx.codegen_fn_attrs(def_id.to_def_id());
 116             debug!(
 117                 "EXPORTED SYMBOL (local): {} ({:?})",
 118                 tcx.symbol_name(Instance::mono(tcx, def_id.to_def_id())),
 119                 export_level
 120             );
 121             (def_id.to_def_id(), SymbolExportInfo {
 122                 level: export_level,
 123                 kind: if tcx.is_static(def_id.to_def_id()) {
 124                     if codegen_attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL) {
 125                         SymbolExportKind::Tls
 126                     } else {
 127                         SymbolExportKind::Data
 128                     }
 129                 } else {
 130                     SymbolExportKind::Text
 131                 },
 132                 used: codegen_attrs.flags.contains(CodegenFnAttrFlags::USED)
 133                     || codegen_attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER) || used,
 134             })
 135         })
 136         .collect();
 137
 138     if let Some(id) = tcx.proc_macro_decls_static(()) {
 139         reachable_non_generics.insert(
 140             id.to_def_id(),
 141             SymbolExportInfo {
 142                 level: SymbolExportLevel::C,
 143                 kind: SymbolExportKind::Data,
 144                 used: false,
 145             },
 146         );
 147     }
 148
 149     reachable_non_generics
 150 }
 151
 152 fn is_reachable_non_generic_provider_local(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
 153     let export_threshold = threshold(tcx);
 154
 155     if let Some(&info) = tcx.reachable_non_generics(def_id.krate).get(&def_id) {
 156         info.level.is_below_threshold(export_threshold)
 157     } else {
 158         false
 159     }
 160 }
 161
 162 fn is_reachable_non_generic_provider_extern(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
 163     tcx.reachable_non_generics(def_id.krate).contains_key(&def_id)
 164 }
 165
 166 fn exported_symbols_provider_local<'tcx>(
 167     tcx: TyCtxt<'tcx>,
 168     cnum: CrateNum,
 169 ) -> &'tcx [(ExportedSymbol<'tcx>, SymbolExportInfo)] {
 170     assert_eq!(cnum, LOCAL_CRATE);
 171
 172     if !tcx.sess.opts.output_types.should_codegen() {
 173         return &[];
 174     }
 175
 176     let mut symbols: Vec<_> = tcx
 177         .reachable_non_generics(LOCAL_CRATE)
 178         .iter()
 179         .map(|(&def_id, &info)| (ExportedSymbol::NonGeneric(def_id), info))
 180         .collect();
 181
 182     if tcx.entry_fn(()).is_some() {
 183         let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, "main"));
 184
 185         symbols.push((
 186             exported_symbol,
 187             SymbolExportInfo {
 188                 level: SymbolExportLevel::C,
 189                 kind: SymbolExportKind::Text,
 190                 used: false,
 191             },
 192         ));
 193     }
 194
 195     if tcx.allocator_kind(()).is_some() {
 196         for symbol_name in ALLOCATOR_METHODS
 197             .iter()
 198             .map(|method| format!("__rust_{}", method.name))
 199             .chain(["__rust_alloc_error_handler".to_string(), OomStrategy::SYMBOL.to_string()])
 200         {
 201             let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, &symbol_name));
 202
 203             symbols.push((
 204                 exported_symbol,
 205                 SymbolExportInfo {
 206                     level: SymbolExportLevel::Rust,
 207                     kind: SymbolExportKind::Text,
 208                     used: false,
 209                 },
 210             ));
 211         }
 212
 213         symbols.push((
 214             ExportedSymbol::NoDefId(SymbolName::new(tcx, OomStrategy::SYMBOL)),
 215             SymbolExportInfo {
 216                 level: SymbolExportLevel::Rust,
 217                 kind: SymbolExportKind::Text,
 218                 used: false,
 219             },
 220         ));
 221     }
 222
 223     if tcx.sess.instrument_coverage() || tcx.sess.opts.cg.profile_generate.enabled() {
 224         // These are weak symbols that point to the profile version and the
 225         // profile name, which need to be treated as exported so LTO doesn't nix
 226         // them.
 227         const PROFILER_WEAK_SYMBOLS: [&str; 2] =
 228             ["__llvm_profile_raw_version", "__llvm_profile_filename"];
 229
 230         symbols.extend(PROFILER_WEAK_SYMBOLS.iter().map(|sym| {
 231             let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, sym));
 232             (
 233                 exported_symbol,
 234                 SymbolExportInfo {
 235                     level: SymbolExportLevel::C,
 236                     kind: SymbolExportKind::Data,
 237                     used: false,
 238                 },
 239             )
 240         }));
 241     }
 242
 243     if tcx.sess.opts.unstable_opts.sanitizer.contains(SanitizerSet::MEMORY) {
 244         let mut msan_weak_symbols = Vec::new();
 245
 246         // Similar to profiling, preserve weak msan symbol during LTO.
 247         if tcx.sess.opts.unstable_opts.sanitizer_recover.contains(SanitizerSet::MEMORY) {
 248             msan_weak_symbols.push("__msan_keep_going");
 249         }
 250
 251         if tcx.sess.opts.unstable_opts.sanitizer_memory_track_origins != 0 {
 252             msan_weak_symbols.push("__msan_track_origins");
 253         }
 254
 255         symbols.extend(msan_weak_symbols.into_iter().map(|sym| {
 256             let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, sym));
 257             (
 258                 exported_symbol,
 259                 SymbolExportInfo {
 260                     level: SymbolExportLevel::C,
 261                     kind: SymbolExportKind::Data,
 262                     used: false,
 263                 },
 264             )
 265         }));
 266     }
 267
 268     if tcx.sess.crate_types().contains(&CrateType::Dylib)
 269         || tcx.sess.crate_types().contains(&CrateType::ProcMacro)
 270     {
 271         let symbol_name = metadata_symbol_name(tcx);
 272         let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, &symbol_name));
 273
 274         symbols.push((
 275             exported_symbol,
 276             SymbolExportInfo {
 277                 level: SymbolExportLevel::C,
 278                 kind: SymbolExportKind::Data,
 279                 used: true,
 280             },
 281         ));
 282     }
 283
 284     if tcx.sess.opts.share_generics() && tcx.local_crate_exports_generics() {
 285         use rustc_middle::mir::mono::{Linkage, MonoItem, Visibility};
 286         use rustc_middle::ty::InstanceDef;
 287
 288         // Normally, we require that shared monomorphizations are not hidden,
 289         // because if we want to re-use a monomorphization from a Rust dylib, it
 290         // needs to be exported.
 291         // However, on platforms that don't allow for Rust dylibs, having
 292         // external linkage is enough for monomorphization to be linked to.
 293         let need_visibility = tcx.sess.target.dynamic_linking && !tcx.sess.target.only_cdylib;
 294
 295         let (_, cgus) = tcx.collect_and_partition_mono_items(());
 296
 297         for (mono_item, &(linkage, visibility)) in cgus.iter().flat_map(|cgu| cgu.items().iter()) {
 298             if linkage != Linkage::External {
 299                 // We can only re-use things with external linkage, otherwise
 300                 // we'll get a linker error
 301                 continue;
 302             }
 303
 304             if need_visibility && visibility == Visibility::Hidden {
 305                 // If we potentially share things from Rust dylibs, they must
 306                 // not be hidden
 307                 continue;
 308             }
 309
 310             match *mono_item {
 311                 MonoItem::Fn(Instance { def: InstanceDef::Item(def), substs }) => {
 312                     if substs.non_erasable_generics().next().is_some() {
 313                         let symbol = ExportedSymbol::Generic(def.did, substs);
 314                         symbols.push((
 315                             symbol,
 316                             SymbolExportInfo {
 317                                 level: SymbolExportLevel::Rust,
 318                                 kind: SymbolExportKind::Text,
 319                                 used: false,
 320                             },
 321                         ));
 322                     }
 323                 }
 324                 MonoItem::Fn(Instance { def: InstanceDef::DropGlue(_, Some(ty)), substs }) => {
 325                     // A little sanity-check
 326                     debug_assert_eq!(
 327                         substs.non_erasable_generics().next(),
 328                         Some(GenericArgKind::Type(ty))
 329                     );
 330                     symbols.push((
 331                         ExportedSymbol::DropGlue(ty),
 332                         SymbolExportInfo {
 333                             level: SymbolExportLevel::Rust,
 334                             kind: SymbolExportKind::Text,
 335                             used: false,
 336                         },
 337                     ));
 338                 }
 339                 _ => {
 340                     // Any other symbols don't qualify for sharing
 341                 }
 342             }
 343         }
 344     }
 345
 346     // Sort so we get a stable incr. comp. hash.
 347     symbols.sort_by_cached_key(|s| s.0.symbol_name_for_local_instance(tcx));
 348
 349     tcx.arena.alloc_from_iter(symbols)
 350 }
 351
 352 fn upstream_monomorphizations_provider(
 353     tcx: TyCtxt<'_>,
 354     (): (),
 355 ) -> DefIdMap<FxHashMap<SubstsRef<'_>, CrateNum>> {
 356     let cnums = tcx.crates(());
 357
 358     let mut instances: DefIdMap<FxHashMap<_, _>> = Default::default();
 359
 360     let drop_in_place_fn_def_id = tcx.lang_items().drop_in_place_fn();
 361
 362     for &cnum in cnums.iter() {
 363         for (exported_symbol, _) in tcx.exported_symbols(cnum).iter() {
 364             let (def_id, substs) = match *exported_symbol {
 365                 ExportedSymbol::Generic(def_id, substs) => (def_id, substs),
 366                 ExportedSymbol::DropGlue(ty) => {
 367                     if let Some(drop_in_place_fn_def_id) = drop_in_place_fn_def_id {
 368                         (drop_in_place_fn_def_id, tcx.intern_substs(&[ty.into()]))
 369                     } else {
 370                         // `drop_in_place` in place does not exist, don't try
 371                         // to use it.
 372                         continue;
 373                     }
 374                 }
 375                 ExportedSymbol::NonGeneric(..) | ExportedSymbol::NoDefId(..) => {
 376                     // These are no monomorphizations
 377                     continue;
 378                 }
 379             };
 380
 381             let substs_map = instances.entry(def_id).or_default();
 382
 383             match substs_map.entry(substs) {
 384                 Occupied(mut e) => {
 385                     // If there are multiple monomorphizations available,
 386                     // we select one deterministically.
 387                     let other_cnum = *e.get();
 388                     if tcx.stable_crate_id(other_cnum) > tcx.stable_crate_id(cnum) {
 389                         e.insert(cnum);
 390                     }
 391                 }
 392                 Vacant(e) => {
 393                     e.insert(cnum);
 394                 }
 395             }
 396         }
 397     }
 398
 399     instances
 400 }
 401
 402 fn upstream_monomorphizations_for_provider(
 403     tcx: TyCtxt<'_>,
 404     def_id: DefId,
 405 ) -> Option<&FxHashMap<SubstsRef<'_>, CrateNum>> {
 406     debug_assert!(!def_id.is_local());
 407     tcx.upstream_monomorphizations(()).get(&def_id)
 408 }
 409
 410 fn upstream_drop_glue_for_provider<'tcx>(
 411     tcx: TyCtxt<'tcx>,
 412     substs: SubstsRef<'tcx>,
 413 ) -> Option<CrateNum> {
 414     if let Some(def_id) = tcx.lang_items().drop_in_place_fn() {
 415         tcx.upstream_monomorphizations_for(def_id).and_then(|monos| monos.get(&substs).cloned())
 416     } else {
 417         None
 418     }
 419 }
 420
 421 fn is_unreachable_local_definition_provider(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
 422     !tcx.reachable_set(()).contains(&def_id)
 423 }
 424
 425 pub fn provide(providers: &mut Providers) {
 426     providers.reachable_non_generics = reachable_non_generics_provider;
 427     providers.is_reachable_non_generic = is_reachable_non_generic_provider_local;
 428     providers.exported_symbols = exported_symbols_provider_local;
 429     providers.upstream_monomorphizations = upstream_monomorphizations_provider;
 430     providers.is_unreachable_local_definition = is_unreachable_local_definition_provider;
 431     providers.upstream_drop_glue_for = upstream_drop_glue_for_provider;
 432     providers.wasm_import_module_map = wasm_import_module_map;
 433 }
 434
 435 pub fn provide_extern(providers: &mut ExternProviders) {
 436     providers.is_reachable_non_generic = is_reachable_non_generic_provider_extern;
 437     providers.upstream_monomorphizations_for = upstream_monomorphizations_for_provider;
 438 }
 439
 440 fn symbol_export_level(tcx: TyCtxt<'_>, sym_def_id: DefId) -> SymbolExportLevel {
 441     // We export anything that's not mangled at the "C" layer as it probably has
 442     // to do with ABI concerns. We do not, however, apply such treatment to
 443     // special symbols in the standard library for various plumbing between
 444     // core/std/allocators/etc. For example symbols used to hook up allocation
 445     // are not considered for export
 446     let codegen_fn_attrs = tcx.codegen_fn_attrs(sym_def_id);
 447     let is_extern = codegen_fn_attrs.contains_extern_indicator();
 448     let std_internal =
 449         codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL);
 450
 451     if is_extern && !std_internal {
 452         let target = &tcx.sess.target.llvm_target;
 453         // WebAssembly cannot export data symbols, so reduce their export level
 454         if target.contains("emscripten") {
 455             if let Some(Node::Item(&hir::Item { kind: hir::ItemKind::Static(..), .. })) =
 456                 tcx.hir().get_if_local(sym_def_id)
 457             {
 458                 return SymbolExportLevel::Rust;
 459             }
 460         }
 461
 462         SymbolExportLevel::C
 463     } else {
 464         SymbolExportLevel::Rust
 465     }
 466 }
 467
 468 /// This is the symbol name of the given instance instantiated in a specific crate.
 469 pub fn symbol_name_for_instance_in_crate<'tcx>(
 470     tcx: TyCtxt<'tcx>,
 471     symbol: ExportedSymbol<'tcx>,
 472     instantiating_crate: CrateNum,
 473 ) -> String {
 474     // If this is something instantiated in the local crate then we might
 475     // already have cached the name as a query result.
 476     if instantiating_crate == LOCAL_CRATE {
 477         return symbol.symbol_name_for_local_instance(tcx).to_string();
 478     }
 479
 480     // This is something instantiated in an upstream crate, so we have to use
 481     // the slower (because uncached) version of computing the symbol name.
 482     match symbol {
 483         ExportedSymbol::NonGeneric(def_id) => {
 484             rustc_symbol_mangling::symbol_name_for_instance_in_crate(
 485                 tcx,
 486                 Instance::mono(tcx, def_id),
 487                 instantiating_crate,
 488             )
 489         }
 490         ExportedSymbol::Generic(def_id, substs) => {
 491             rustc_symbol_mangling::symbol_name_for_instance_in_crate(
 492                 tcx,
 493                 Instance::new(def_id, substs),
 494                 instantiating_crate,
 495             )
 496         }
 497         ExportedSymbol::DropGlue(ty) => rustc_symbol_mangling::symbol_name_for_instance_in_crate(
 498             tcx,
 499             Instance::resolve_drop_in_place(tcx, ty),
 500             instantiating_crate,
 501         ),
 502         ExportedSymbol::NoDefId(symbol_name) => symbol_name.to_string(),
 503     }
 504 }
 505
 506 /// This is the symbol name of the given instance as seen by the linker.
 507 ///
 508 /// On 32-bit Windows symbols are decorated according to their calling conventions.
 509 pub fn linking_symbol_name_for_instance_in_crate<'tcx>(
 510     tcx: TyCtxt<'tcx>,
 511     symbol: ExportedSymbol<'tcx>,
 512     instantiating_crate: CrateNum,
 513 ) -> String {
 514     use rustc_target::abi::call::Conv;
 515
 516     let mut undecorated = symbol_name_for_instance_in_crate(tcx, symbol, instantiating_crate);
 517
 518     let target = &tcx.sess.target;
 519     if !target.is_like_windows {
 520         // Mach-O has a global "_" suffix and `object` crate will handle it.
 521         // ELF does not have any symbol decorations.
 522         return undecorated;
 523     }
 524
 525     let x86 = match &target.arch[..] {
 526         "x86" => true,
 527         "x86_64" => false,
 528         // Only x86/64 use symbol decorations.
 529         _ => return undecorated,
 530     };
 531
 532     let instance = match symbol {
 533         ExportedSymbol::NonGeneric(def_id) | ExportedSymbol::Generic(def_id, _)
 534             if tcx.is_static(def_id) =>
 535         {
 536             None
 537         }
 538         ExportedSymbol::NonGeneric(def_id) => Some(Instance::mono(tcx, def_id)),
 539         ExportedSymbol::Generic(def_id, substs) => Some(Instance::new(def_id, substs)),
 540         // DropGlue always use the Rust calling convention and thus follow the target's default
 541         // symbol decoration scheme.
 542         ExportedSymbol::DropGlue(..) => None,
 543         // NoDefId always follow the target's default symbol decoration scheme.
 544         ExportedSymbol::NoDefId(..) => None,
 545     };
 546
 547     let (conv, args) = instance
 548         .map(|i| {
 549             tcx.fn_abi_of_instance(ty::ParamEnv::reveal_all().and((i, ty::List::empty())))
 550                 .unwrap_or_else(|_| bug!("fn_abi_of_instance({i:?}) failed"))
 551         })
 552         .map(|fnabi| (fnabi.conv, &fnabi.args[..]))
 553         .unwrap_or((Conv::Rust, &[]));
 554
 555     // Decorate symbols with prefixes, suffixes and total number of bytes of arguments.
 556     // Reference: https://docs.microsoft.com/en-us/cpp/build/reference/decorated-names?view=msvc-170
 557     let (prefix, suffix) = match conv {
 558         Conv::X86Fastcall => ("@", "@"),
 559         Conv::X86Stdcall => ("_", "@"),
 560         Conv::X86VectorCall => ("", "@@"),
 561         _ => {
 562             if x86 {
 563                 undecorated.insert(0, '_');
 564             }
 565             return undecorated;
 566         }
 567     };
 568
 569     let args_in_bytes: u64 = args
 570         .iter()
 571         .map(|abi| abi.layout.size.bytes().next_multiple_of(target.pointer_width as u64 / 8))
 572         .sum();
 573     format!("{prefix}{undecorated}{suffix}{args_in_bytes}")
 574 }
 575
 576 fn wasm_import_module_map(tcx: TyCtxt<'_>, cnum: CrateNum) -> FxHashMap<DefId, String> {
 577     // Build up a map from DefId to a `NativeLib` structure, where
 578     // `NativeLib` internally contains information about
 579     // `#[link(wasm_import_module = "...")]` for example.
 580     let native_libs = tcx.native_libraries(cnum);
 581
 582     let def_id_to_native_lib = native_libs
 583         .iter()
 584         .filter_map(|lib| lib.foreign_module.map(|id| (id, lib)))
 585         .collect::<FxHashMap<_, _>>();
 586
 587     let mut ret = FxHashMap::default();
 588     for (def_id, lib) in tcx.foreign_modules(cnum).iter() {
 589         let module = def_id_to_native_lib.get(&def_id).and_then(|s| s.wasm_import_module);
 590         let Some(module) = module else { continue };
 591         ret.extend(lib.foreign_items.iter().map(|id| {
 592             assert_eq!(id.krate, cnum);
 593             (*id, module.to_string())
 594         }));
 595     }
 596
 597     ret
 598 }