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 =
 184             ExportedSymbol::NoDefId(SymbolName::new(tcx, tcx.sess.target.entry_name.as_ref()));
 185
 186         symbols.push((
 187             exported_symbol,
 188             SymbolExportInfo {
 189                 level: SymbolExportLevel::C,
 190                 kind: SymbolExportKind::Text,
 191                 used: false,
 192             },
 193         ));
 194     }
 195
 196     if tcx.allocator_kind(()).is_some() {
 197         for symbol_name in ALLOCATOR_METHODS
 198             .iter()
 199             .map(|method| format!("__rust_{}", method.name))
 200             .chain(["__rust_alloc_error_handler".to_string(), OomStrategy::SYMBOL.to_string()])
 201         {
 202             let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, &symbol_name));
 203
 204             symbols.push((
 205                 exported_symbol,
 206                 SymbolExportInfo {
 207                     level: SymbolExportLevel::Rust,
 208                     kind: SymbolExportKind::Text,
 209                     used: false,
 210                 },
 211             ));
 212         }
 213
 214         symbols.push((
 215             ExportedSymbol::NoDefId(SymbolName::new(tcx, OomStrategy::SYMBOL)),
 216             SymbolExportInfo {
 217                 level: SymbolExportLevel::Rust,
 218                 kind: SymbolExportKind::Text,
 219                 used: false,
 220             },
 221         ));
 222     }
 223
 224     if tcx.sess.instrument_coverage() || tcx.sess.opts.cg.profile_generate.enabled() {
 225         // These are weak symbols that point to the profile version and the
 226         // profile name, which need to be treated as exported so LTO doesn't nix
 227         // them.
 228         const PROFILER_WEAK_SYMBOLS: [&str; 2] =
 229             ["__llvm_profile_raw_version", "__llvm_profile_filename"];
 230
 231         symbols.extend(PROFILER_WEAK_SYMBOLS.iter().map(|sym| {
 232             let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, sym));
 233             (
 234                 exported_symbol,
 235                 SymbolExportInfo {
 236                     level: SymbolExportLevel::C,
 237                     kind: SymbolExportKind::Data,
 238                     used: false,
 239                 },
 240             )
 241         }));
 242     }
 243
 244     if tcx.sess.opts.unstable_opts.sanitizer.contains(SanitizerSet::MEMORY) {
 245         let mut msan_weak_symbols = Vec::new();
 246
 247         // Similar to profiling, preserve weak msan symbol during LTO.
 248         if tcx.sess.opts.unstable_opts.sanitizer_recover.contains(SanitizerSet::MEMORY) {
 249             msan_weak_symbols.push("__msan_keep_going");
 250         }
 251
 252         if tcx.sess.opts.unstable_opts.sanitizer_memory_track_origins != 0 {
 253             msan_weak_symbols.push("__msan_track_origins");
 254         }
 255
 256         symbols.extend(msan_weak_symbols.into_iter().map(|sym| {
 257             let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, sym));
 258             (
 259                 exported_symbol,
 260                 SymbolExportInfo {
 261                     level: SymbolExportLevel::C,
 262                     kind: SymbolExportKind::Data,
 263                     used: false,
 264                 },
 265             )
 266         }));
 267     }
 268
 269     if tcx.sess.crate_types().contains(&CrateType::Dylib)
 270         || tcx.sess.crate_types().contains(&CrateType::ProcMacro)
 271     {
 272         let symbol_name = metadata_symbol_name(tcx);
 273         let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, &symbol_name));
 274
 275         symbols.push((
 276             exported_symbol,
 277             SymbolExportInfo {
 278                 level: SymbolExportLevel::C,
 279                 kind: SymbolExportKind::Data,
 280                 used: true,
 281             },
 282         ));
 283     }
 284
 285     if tcx.sess.opts.share_generics() && tcx.local_crate_exports_generics() {
 286         use rustc_middle::mir::mono::{Linkage, MonoItem, Visibility};
 287         use rustc_middle::ty::InstanceDef;
 288
 289         // Normally, we require that shared monomorphizations are not hidden,
 290         // because if we want to re-use a monomorphization from a Rust dylib, it
 291         // needs to be exported.
 292         // However, on platforms that don't allow for Rust dylibs, having
 293         // external linkage is enough for monomorphization to be linked to.
 294         let need_visibility = tcx.sess.target.dynamic_linking && !tcx.sess.target.only_cdylib;
 295
 296         let (_, cgus) = tcx.collect_and_partition_mono_items(());
 297
 298         for (mono_item, &(linkage, visibility)) in cgus.iter().flat_map(|cgu| cgu.items().iter()) {
 299             if linkage != Linkage::External {
 300                 // We can only re-use things with external linkage, otherwise
 301                 // we'll get a linker error
 302                 continue;
 303             }
 304
 305             if need_visibility && visibility == Visibility::Hidden {
 306                 // If we potentially share things from Rust dylibs, they must
 307                 // not be hidden
 308                 continue;
 309             }
 310
 311             match *mono_item {
 312                 MonoItem::Fn(Instance { def: InstanceDef::Item(def), substs }) => {
 313                     if substs.non_erasable_generics().next().is_some() {
 314                         let symbol = ExportedSymbol::Generic(def.did, substs);
 315                         symbols.push((
 316                             symbol,
 317                             SymbolExportInfo {
 318                                 level: SymbolExportLevel::Rust,
 319                                 kind: SymbolExportKind::Text,
 320                                 used: false,
 321                             },
 322                         ));
 323                     }
 324                 }
 325                 MonoItem::Fn(Instance { def: InstanceDef::DropGlue(_, Some(ty)), substs }) => {
 326                     // A little sanity-check
 327                     debug_assert_eq!(
 328                         substs.non_erasable_generics().next(),
 329                         Some(GenericArgKind::Type(ty))
 330                     );
 331                     symbols.push((
 332                         ExportedSymbol::DropGlue(ty),
 333                         SymbolExportInfo {
 334                             level: SymbolExportLevel::Rust,
 335                             kind: SymbolExportKind::Text,
 336                             used: false,
 337                         },
 338                     ));
 339                 }
 340                 _ => {
 341                     // Any other symbols don't qualify for sharing
 342                 }
 343             }
 344         }
 345     }
 346
 347     // Sort so we get a stable incr. comp. hash.
 348     symbols.sort_by_cached_key(|s| s.0.symbol_name_for_local_instance(tcx));
 349
 350     tcx.arena.alloc_from_iter(symbols)
 351 }
 352
 353 fn upstream_monomorphizations_provider(
 354     tcx: TyCtxt<'_>,
 355     (): (),
 356 ) -> DefIdMap<FxHashMap<SubstsRef<'_>, CrateNum>> {
 357     let cnums = tcx.crates(());
 358
 359     let mut instances: DefIdMap<FxHashMap<_, _>> = Default::default();
 360
 361     let drop_in_place_fn_def_id = tcx.lang_items().drop_in_place_fn();
 362
 363     for &cnum in cnums.iter() {
 364         for (exported_symbol, _) in tcx.exported_symbols(cnum).iter() {
 365             let (def_id, substs) = match *exported_symbol {
 366                 ExportedSymbol::Generic(def_id, substs) => (def_id, substs),
 367                 ExportedSymbol::DropGlue(ty) => {
 368                     if let Some(drop_in_place_fn_def_id) = drop_in_place_fn_def_id {
 369                         (drop_in_place_fn_def_id, tcx.intern_substs(&[ty.into()]))
 370                     } else {
 371                         // `drop_in_place` in place does not exist, don't try
 372                         // to use it.
 373                         continue;
 374                     }
 375                 }
 376                 ExportedSymbol::NonGeneric(..) | ExportedSymbol::NoDefId(..) => {
 377                     // These are no monomorphizations
 378                     continue;
 379                 }
 380             };
 381
 382             let substs_map = instances.entry(def_id).or_default();
 383
 384             match substs_map.entry(substs) {
 385                 Occupied(mut e) => {
 386                     // If there are multiple monomorphizations available,
 387                     // we select one deterministically.
 388                     let other_cnum = *e.get();
 389                     if tcx.stable_crate_id(other_cnum) > tcx.stable_crate_id(cnum) {
 390                         e.insert(cnum);
 391                     }
 392                 }
 393                 Vacant(e) => {
 394                     e.insert(cnum);
 395                 }
 396             }
 397         }
 398     }
 399
 400     instances
 401 }
 402
 403 fn upstream_monomorphizations_for_provider(
 404     tcx: TyCtxt<'_>,
 405     def_id: DefId,
 406 ) -> Option<&FxHashMap<SubstsRef<'_>, CrateNum>> {
 407     debug_assert!(!def_id.is_local());
 408     tcx.upstream_monomorphizations(()).get(&def_id)
 409 }
 410
 411 fn upstream_drop_glue_for_provider<'tcx>(
 412     tcx: TyCtxt<'tcx>,
 413     substs: SubstsRef<'tcx>,
 414 ) -> Option<CrateNum> {
 415     if let Some(def_id) = tcx.lang_items().drop_in_place_fn() {
 416         tcx.upstream_monomorphizations_for(def_id).and_then(|monos| monos.get(&substs).cloned())
 417     } else {
 418         None
 419     }
 420 }
 421
 422 fn is_unreachable_local_definition_provider(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
 423     !tcx.reachable_set(()).contains(&def_id)
 424 }
 425
 426 pub fn provide(providers: &mut Providers) {
 427     providers.reachable_non_generics = reachable_non_generics_provider;
 428     providers.is_reachable_non_generic = is_reachable_non_generic_provider_local;
 429     providers.exported_symbols = exported_symbols_provider_local;
 430     providers.upstream_monomorphizations = upstream_monomorphizations_provider;
 431     providers.is_unreachable_local_definition = is_unreachable_local_definition_provider;
 432     providers.upstream_drop_glue_for = upstream_drop_glue_for_provider;
 433     providers.wasm_import_module_map = wasm_import_module_map;
 434 }
 435
 436 pub fn provide_extern(providers: &mut ExternProviders) {
 437     providers.is_reachable_non_generic = is_reachable_non_generic_provider_extern;
 438     providers.upstream_monomorphizations_for = upstream_monomorphizations_for_provider;
 439 }
 440
 441 fn symbol_export_level(tcx: TyCtxt<'_>, sym_def_id: DefId) -> SymbolExportLevel {
 442     // We export anything that's not mangled at the "C" layer as it probably has
 443     // to do with ABI concerns. We do not, however, apply such treatment to
 444     // special symbols in the standard library for various plumbing between
 445     // core/std/allocators/etc. For example symbols used to hook up allocation
 446     // are not considered for export
 447     let codegen_fn_attrs = tcx.codegen_fn_attrs(sym_def_id);
 448     let is_extern = codegen_fn_attrs.contains_extern_indicator();
 449     let std_internal =
 450         codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL);
 451
 452     if is_extern && !std_internal {
 453         let target = &tcx.sess.target.llvm_target;
 454         // WebAssembly cannot export data symbols, so reduce their export level
 455         if target.contains("emscripten") {
 456             if let Some(Node::Item(&hir::Item { kind: hir::ItemKind::Static(..), .. })) =
 457                 tcx.hir().get_if_local(sym_def_id)
 458             {
 459                 return SymbolExportLevel::Rust;
 460             }
 461         }
 462
 463         SymbolExportLevel::C
 464     } else {
 465         SymbolExportLevel::Rust
 466     }
 467 }
 468
 469 /// This is the symbol name of the given instance instantiated in a specific crate.
 470 pub fn symbol_name_for_instance_in_crate<'tcx>(
 471     tcx: TyCtxt<'tcx>,
 472     symbol: ExportedSymbol<'tcx>,
 473     instantiating_crate: CrateNum,
 474 ) -> String {
 475     // If this is something instantiated in the local crate then we might
 476     // already have cached the name as a query result.
 477     if instantiating_crate == LOCAL_CRATE {
 478         return symbol.symbol_name_for_local_instance(tcx).to_string();
 479     }
 480
 481     // This is something instantiated in an upstream crate, so we have to use
 482     // the slower (because uncached) version of computing the symbol name.
 483     match symbol {
 484         ExportedSymbol::NonGeneric(def_id) => {
 485             rustc_symbol_mangling::symbol_name_for_instance_in_crate(
 486                 tcx,
 487                 Instance::mono(tcx, def_id),
 488                 instantiating_crate,
 489             )
 490         }
 491         ExportedSymbol::Generic(def_id, substs) => {
 492             rustc_symbol_mangling::symbol_name_for_instance_in_crate(
 493                 tcx,
 494                 Instance::new(def_id, substs),
 495                 instantiating_crate,
 496             )
 497         }
 498         ExportedSymbol::DropGlue(ty) => rustc_symbol_mangling::symbol_name_for_instance_in_crate(
 499             tcx,
 500             Instance::resolve_drop_in_place(tcx, ty),
 501             instantiating_crate,
 502         ),
 503         ExportedSymbol::NoDefId(symbol_name) => symbol_name.to_string(),
 504     }
 505 }
 506
 507 /// This is the symbol name of the given instance as seen by the linker.
 508 ///
 509 /// On 32-bit Windows symbols are decorated according to their calling conventions.
 510 pub fn linking_symbol_name_for_instance_in_crate<'tcx>(
 511     tcx: TyCtxt<'tcx>,
 512     symbol: ExportedSymbol<'tcx>,
 513     instantiating_crate: CrateNum,
 514 ) -> String {
 515     use rustc_target::abi::call::Conv;
 516
 517     let mut undecorated = symbol_name_for_instance_in_crate(tcx, symbol, instantiating_crate);
 518
 519     let target = &tcx.sess.target;
 520     if !target.is_like_windows {
 521         // Mach-O has a global "_" suffix and `object` crate will handle it.
 522         // ELF does not have any symbol decorations.
 523         return undecorated;
 524     }
 525
 526     let x86 = match &target.arch[..] {
 527         "x86" => true,
 528         "x86_64" => false,
 529         // Only x86/64 use symbol decorations.
 530         _ => return undecorated,
 531     };
 532
 533     let instance = match symbol {
 534         ExportedSymbol::NonGeneric(def_id) | ExportedSymbol::Generic(def_id, _)
 535             if tcx.is_static(def_id) =>
 536         {
 537             None
 538         }
 539         ExportedSymbol::NonGeneric(def_id) => Some(Instance::mono(tcx, def_id)),
 540         ExportedSymbol::Generic(def_id, substs) => Some(Instance::new(def_id, substs)),
 541         // DropGlue always use the Rust calling convention and thus follow the target's default
 542         // symbol decoration scheme.
 543         ExportedSymbol::DropGlue(..) => None,
 544         // NoDefId always follow the target's default symbol decoration scheme.
 545         ExportedSymbol::NoDefId(..) => None,
 546     };
 547
 548     let (conv, args) = instance
 549         .map(|i| {
 550             tcx.fn_abi_of_instance(ty::ParamEnv::reveal_all().and((i, ty::List::empty())))
 551                 .unwrap_or_else(|_| bug!("fn_abi_of_instance({i:?}) failed"))
 552         })
 553         .map(|fnabi| (fnabi.conv, &fnabi.args[..]))
 554         .unwrap_or((Conv::Rust, &[]));
 555
 556     // Decorate symbols with prefixes, suffixes and total number of bytes of arguments.
 557     // Reference: https://docs.microsoft.com/en-us/cpp/build/reference/decorated-names?view=msvc-170
 558     let (prefix, suffix) = match conv {
 559         Conv::X86Fastcall => ("@", "@"),
 560         Conv::X86Stdcall => ("_", "@"),
 561         Conv::X86VectorCall => ("", "@@"),
 562         _ => {
 563             if x86 {
 564                 undecorated.insert(0, '_');
 565             }
 566             return undecorated;
 567         }
 568     };
 569
 570     let args_in_bytes: u64 = args
 571         .iter()
 572         .map(|abi| abi.layout.size.bytes().next_multiple_of(target.pointer_width as u64 / 8))
 573         .sum();
 574     format!("{prefix}{undecorated}{suffix}{args_in_bytes}")
 575 }
 576
 577 fn wasm_import_module_map(tcx: TyCtxt<'_>, cnum: CrateNum) -> FxHashMap<DefId, String> {
 578     // Build up a map from DefId to a `NativeLib` structure, where
 579     // `NativeLib` internally contains information about
 580     // `#[link(wasm_import_module = "...")]` for example.
 581     let native_libs = tcx.native_libraries(cnum);
 582
 583     let def_id_to_native_lib = native_libs
 584         .iter()
 585         .filter_map(|lib| lib.foreign_module.map(|id| (id, lib)))
 586         .collect::<FxHashMap<_, _>>();
 587
 588     let mut ret = FxHashMap::default();
 589     for (def_id, lib) in tcx.foreign_modules(cnum).iter() {
 590         let module = def_id_to_native_lib.get(&def_id).and_then(|s| s.wasm_import_module);
 591         let Some(module) = module else { continue };
 592         ret.extend(lib.foreign_items.iter().map(|id| {
 593             assert_eq!(id.krate, cnum);
 594             (*id, module.to_string())
 595         }));
 596     }
 597
 598     ret
 599 }