src/librustc_codegen_ssa/back/symbol_export.rs

   1 use std::collections::hash_map::Entry::*;
   2 use std::sync::Arc;
   3
   4 use rustc::ty::Instance;
   5 use rustc::hir;
   6 use rustc::hir::Node;
   7 use rustc::hir::CodegenFnAttrFlags;
   8 use rustc::hir::def_id::{CrateNum, DefId, LOCAL_CRATE, CRATE_DEF_INDEX};
   9 use rustc_data_structures::fingerprint::Fingerprint;
  10 use rustc::middle::exported_symbols::{SymbolExportLevel, ExportedSymbol, metadata_symbol_name};
  11 use rustc::session::config;
  12 use rustc::ty::{TyCtxt, SymbolName};
  13 use rustc::ty::query::Providers;
  14 use rustc::ty::subst::SubstsRef;
  15 use rustc::util::nodemap::{FxHashMap, DefIdMap};
  16 use rustc_index::vec::IndexVec;
  17 use syntax::expand::allocator::ALLOCATOR_METHODS;
  18
  19 pub type ExportedSymbols = FxHashMap<
  20     CrateNum,
  21     Arc<Vec<(String, SymbolExportLevel)>>,
  22 >;
  23
  24 pub fn threshold(tcx: TyCtxt<'_>) -> SymbolExportLevel {
  25     crates_export_threshold(&tcx.sess.crate_types.borrow())
  26 }
  27
  28 fn crate_export_threshold(crate_type: config::CrateType) -> SymbolExportLevel {
  29     match crate_type {
  30         config::CrateType::Executable |
  31         config::CrateType::Staticlib  |
  32         config::CrateType::ProcMacro  |
  33         config::CrateType::Cdylib     => SymbolExportLevel::C,
  34         config::CrateType::Rlib       |
  35         config::CrateType::Dylib      => SymbolExportLevel::Rust,
  36     }
  37 }
  38
  39 pub fn crates_export_threshold(crate_types: &[config::CrateType]) -> SymbolExportLevel {
  40     if crate_types.iter().any(|&crate_type|
  41         crate_export_threshold(crate_type) == SymbolExportLevel::Rust)
  42     {
  43         SymbolExportLevel::Rust
  44     } else {
  45         SymbolExportLevel::C
  46     }
  47 }
  48
  49 fn reachable_non_generics_provider(
  50     tcx: TyCtxt<'_>,
  51     cnum: CrateNum,
  52 ) -> &DefIdMap<SymbolExportLevel> {
  53     assert_eq!(cnum, LOCAL_CRATE);
  54
  55     if !tcx.sess.opts.output_types.should_codegen() {
  56         return tcx.arena.alloc(Default::default());
  57     }
  58
  59     // Check to see if this crate is a "special runtime crate". These
  60     // crates, implementation details of the standard library, typically
  61     // have a bunch of `pub extern` and `#[no_mangle]` functions as the
  62     // ABI between them. We don't want their symbols to have a `C`
  63     // export level, however, as they're just implementation details.
  64     // Down below we'll hardwire all of the symbols to the `Rust` export
  65     // level instead.
  66     let special_runtime_crate = tcx.is_panic_runtime(LOCAL_CRATE) ||
  67         tcx.is_compiler_builtins(LOCAL_CRATE);
  68
  69     let mut reachable_non_generics: DefIdMap<_> = tcx.reachable_set(LOCAL_CRATE).0
  70         .iter()
  71         .filter_map(|&hir_id| {
  72             // We want to ignore some FFI functions that are not exposed from
  73             // this crate. Reachable FFI functions can be lumped into two
  74             // categories:
  75             //
  76             // 1. Those that are included statically via a static library
  77             // 2. Those included otherwise (e.g., dynamically or via a framework)
  78             //
  79             // Although our LLVM module is not literally emitting code for the
  80             // statically included symbols, it's an export of our library which
  81             // needs to be passed on to the linker and encoded in the metadata.
  82             //
  83             // As a result, if this id is an FFI item (foreign item) then we only
  84             // let it through if it's included statically.
  85             match tcx.hir().get(hir_id) {
  86                 Node::ForeignItem(..) => {
  87                     let def_id = tcx.hir().local_def_id(hir_id);
  88                     tcx.is_statically_included_foreign_item(def_id).then_some(def_id)
  89                 }
  90
  91                 // Only consider nodes that actually have exported symbols.
  92                 Node::Item(&hir::Item {
  93                     kind: hir::ItemKind::Static(..),
  94                     ..
  95                 }) |
  96                 Node::Item(&hir::Item {
  97                     kind: hir::ItemKind::Fn(..), ..
  98                 }) |
  99                 Node::ImplItem(&hir::ImplItem {
 100                     kind: hir::ImplItemKind::Method(..),
 101                     ..
 102                 }) => {
 103                     let def_id = tcx.hir().local_def_id(hir_id);
 104                     let generics = tcx.generics_of(def_id);
 105                     if !generics.requires_monomorphization(tcx) &&
 106                         // Functions marked with #[inline] are only ever codegened
 107                         // with "internal" linkage and are never exported.
 108                         !Instance::mono(tcx, def_id).def.requires_local(tcx) {
 109                         Some(def_id)
 110                     } else {
 111                         None
 112                     }
 113                 }
 114
 115                 _ => None
 116             }
 117         })
 118         .map(|def_id| {
 119             let export_level = if special_runtime_crate {
 120                 let name = tcx.symbol_name(Instance::mono(tcx, def_id)).name.as_str();
 121                 // We can probably do better here by just ensuring that
 122                 // it has hidden visibility rather than public
 123                 // visibility, as this is primarily here to ensure it's
 124                 // not stripped during LTO.
 125                 //
 126                 // In general though we won't link right if these
 127                 // symbols are stripped, and LTO currently strips them.
 128                 if name == "rust_eh_personality" ||
 129                    name == "rust_eh_register_frames" ||
 130                    name == "rust_eh_unregister_frames" {
 131                     SymbolExportLevel::C
 132                 } else {
 133                     SymbolExportLevel::Rust
 134                 }
 135             } else {
 136                 symbol_export_level(tcx, def_id)
 137             };
 138             debug!("EXPORTED SYMBOL (local): {} ({:?})",
 139                    tcx.symbol_name(Instance::mono(tcx, def_id)),
 140                    export_level);
 141             (def_id, export_level)
 142         })
 143         .collect();
 144
 145     if let Some(id) = tcx.proc_macro_decls_static(LOCAL_CRATE) {
 146         reachable_non_generics.insert(id, SymbolExportLevel::C);
 147     }
 148
 149     if let Some(id) = tcx.plugin_registrar_fn(LOCAL_CRATE) {
 150         reachable_non_generics.insert(id, SymbolExportLevel::C);
 151     }
 152
 153     tcx.arena.alloc(reachable_non_generics)
 154 }
 155
 156 fn is_reachable_non_generic_provider_local(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
 157     let export_threshold = threshold(tcx);
 158
 159     if let Some(&level) = tcx.reachable_non_generics(def_id.krate).get(&def_id) {
 160         level.is_below_threshold(export_threshold)
 161     } else {
 162         false
 163     }
 164 }
 165
 166 fn is_reachable_non_generic_provider_extern(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
 167     tcx.reachable_non_generics(def_id.krate).contains_key(&def_id)
 168 }
 169
 170 fn exported_symbols_provider_local(
 171     tcx: TyCtxt<'_>,
 172     cnum: CrateNum,
 173 ) -> Arc<Vec<(ExportedSymbol<'_>, SymbolExportLevel)>> {
 174     assert_eq!(cnum, LOCAL_CRATE);
 175
 176     if !tcx.sess.opts.output_types.should_codegen() {
 177         return Arc::new(vec![])
 178     }
 179
 180     let mut symbols: Vec<_> = tcx.reachable_non_generics(LOCAL_CRATE)
 181                                  .iter()
 182                                  .map(|(&def_id, &level)| {
 183                                     (ExportedSymbol::NonGeneric(def_id), level)
 184                                  })
 185                                  .collect();
 186
 187     if tcx.entry_fn(LOCAL_CRATE).is_some() {
 188         let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new("main"));
 189
 190         symbols.push((exported_symbol, SymbolExportLevel::C));
 191     }
 192
 193     if tcx.allocator_kind().is_some() {
 194         for method in ALLOCATOR_METHODS {
 195             let symbol_name = format!("__rust_{}", method.name);
 196             let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(&symbol_name));
 197
 198             symbols.push((exported_symbol, SymbolExportLevel::Rust));
 199         }
 200     }
 201
 202     if tcx.sess.opts.cg.profile_generate.enabled() {
 203         // These are weak symbols that point to the profile version and the
 204         // profile name, which need to be treated as exported so LTO doesn't nix
 205         // them.
 206         const PROFILER_WEAK_SYMBOLS: [&str; 2] = [
 207             "__llvm_profile_raw_version",
 208             "__llvm_profile_filename",
 209         ];
 210
 211         symbols.extend(PROFILER_WEAK_SYMBOLS.iter().map(|sym| {
 212             let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(sym));
 213             (exported_symbol, SymbolExportLevel::C)
 214         }));
 215     }
 216
 217     if tcx.sess.crate_types.borrow().contains(&config::CrateType::Dylib) {
 218         let symbol_name = metadata_symbol_name(tcx);
 219         let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(&symbol_name));
 220
 221         symbols.push((exported_symbol, SymbolExportLevel::Rust));
 222     }
 223
 224     if tcx.sess.opts.share_generics() && tcx.local_crate_exports_generics() {
 225         use rustc::mir::mono::{Linkage, Visibility, MonoItem};
 226         use rustc::ty::InstanceDef;
 227
 228         // Normally, we require that shared monomorphizations are not hidden,
 229         // because if we want to re-use a monomorphization from a Rust dylib, it
 230         // needs to be exported.
 231         // However, on platforms that don't allow for Rust dylibs, having
 232         // external linkage is enough for monomorphization to be linked to.
 233         let need_visibility = tcx.sess.target.target.options.dynamic_linking &&
 234                               !tcx.sess.target.target.options.only_cdylib;
 235
 236         let (_, cgus) = tcx.collect_and_partition_mono_items(LOCAL_CRATE);
 237
 238         for (mono_item, &(linkage, visibility)) in cgus.iter()
 239                                                        .flat_map(|cgu| cgu.items().iter()) {
 240             if linkage != Linkage::External {
 241                 // We can only re-use things with external linkage, otherwise
 242                 // we'll get a linker error
 243                 continue
 244             }
 245
 246             if need_visibility && visibility == Visibility::Hidden {
 247                 // If we potentially share things from Rust dylibs, they must
 248                 // not be hidden
 249                 continue
 250             }
 251
 252             if let &MonoItem::Fn(Instance {
 253                 def: InstanceDef::Item(def_id),
 254                 substs,
 255             }) = mono_item {
 256                 if substs.non_erasable_generics().next().is_some() {
 257                     symbols.push((ExportedSymbol::Generic(def_id, substs),
 258                                   SymbolExportLevel::Rust));
 259                 }
 260             }
 261         }
 262     }
 263
 264     // Sort so we get a stable incr. comp. hash.
 265     symbols.sort_unstable_by(|&(ref symbol1, ..), &(ref symbol2, ..)| {
 266         symbol1.compare_stable(tcx, symbol2)
 267     });
 268
 269     Arc::new(symbols)
 270 }
 271
 272 fn upstream_monomorphizations_provider(
 273     tcx: TyCtxt<'_>,
 274     cnum: CrateNum,
 275 ) -> &DefIdMap<FxHashMap<SubstsRef<'_>, CrateNum>> {
 276     debug_assert!(cnum == LOCAL_CRATE);
 277
 278     let cnums = tcx.all_crate_nums(LOCAL_CRATE);
 279
 280     let mut instances: DefIdMap<FxHashMap<_, _>> = Default::default();
 281
 282     let cnum_stable_ids: IndexVec<CrateNum, Fingerprint> = {
 283         let mut cnum_stable_ids = IndexVec::from_elem_n(Fingerprint::ZERO,
 284                                                         cnums.len() + 1);
 285
 286         for &cnum in cnums.iter() {
 287             cnum_stable_ids[cnum] = tcx.def_path_hash(DefId {
 288                 krate: cnum,
 289                 index: CRATE_DEF_INDEX,
 290             }).0;
 291         }
 292
 293         cnum_stable_ids
 294     };
 295
 296     for &cnum in cnums.iter() {
 297         for (exported_symbol, _) in tcx.exported_symbols(cnum).iter() {
 298             if let &ExportedSymbol::Generic(def_id, substs) = exported_symbol {
 299                 let substs_map = instances.entry(def_id).or_default();
 300
 301                 match substs_map.entry(substs) {
 302                     Occupied(mut e) => {
 303                         // If there are multiple monomorphizations available,
 304                         // we select one deterministically.
 305                         let other_cnum = *e.get();
 306                         if cnum_stable_ids[other_cnum] > cnum_stable_ids[cnum] {
 307                             e.insert(cnum);
 308                         }
 309                     }
 310                     Vacant(e) => {
 311                         e.insert(cnum);
 312                     }
 313                 }
 314             }
 315         }
 316     }
 317
 318     tcx.arena.alloc(instances)
 319 }
 320
 321 fn upstream_monomorphizations_for_provider(
 322     tcx: TyCtxt<'_>,
 323     def_id: DefId,
 324 ) -> Option<&FxHashMap<SubstsRef<'_>, CrateNum>> {
 325     debug_assert!(!def_id.is_local());
 326     tcx.upstream_monomorphizations(LOCAL_CRATE).get(&def_id)
 327 }
 328
 329 fn is_unreachable_local_definition_provider(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
 330     if let Some(hir_id) = tcx.hir().as_local_hir_id(def_id) {
 331         !tcx.reachable_set(LOCAL_CRATE).0.contains(&hir_id)
 332     } else {
 333         bug!("is_unreachable_local_definition called with non-local DefId: {:?}",
 334              def_id)
 335     }
 336 }
 337
 338 pub fn provide(providers: &mut Providers<'_>) {
 339     providers.reachable_non_generics = reachable_non_generics_provider;
 340     providers.is_reachable_non_generic = is_reachable_non_generic_provider_local;
 341     providers.exported_symbols = exported_symbols_provider_local;
 342     providers.upstream_monomorphizations = upstream_monomorphizations_provider;
 343     providers.is_unreachable_local_definition = is_unreachable_local_definition_provider;
 344 }
 345
 346 pub fn provide_extern(providers: &mut Providers<'_>) {
 347     providers.is_reachable_non_generic = is_reachable_non_generic_provider_extern;
 348     providers.upstream_monomorphizations_for = upstream_monomorphizations_for_provider;
 349 }
 350
 351 fn symbol_export_level(tcx: TyCtxt<'_>, sym_def_id: DefId) -> SymbolExportLevel {
 352     // We export anything that's not mangled at the "C" layer as it probably has
 353     // to do with ABI concerns. We do not, however, apply such treatment to
 354     // special symbols in the standard library for various plumbing between
 355     // core/std/allocators/etc. For example symbols used to hook up allocation
 356     // are not considered for export
 357     let codegen_fn_attrs = tcx.codegen_fn_attrs(sym_def_id);
 358     let is_extern = codegen_fn_attrs.contains_extern_indicator();
 359     let std_internal =
 360         codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL);
 361
 362     if is_extern && !std_internal {
 363         let target = &tcx.sess.target.target.llvm_target;
 364         // WebAssembly cannot export data symbols, so reduce their export level
 365         if target.contains("wasm32") || target.contains("emscripten") {
 366             if let Some(Node::Item(&hir::Item {
 367                 kind: hir::ItemKind::Static(..),
 368                 ..
 369             })) = tcx.hir().get_if_local(sym_def_id) {
 370                 return SymbolExportLevel::Rust;
 371             }
 372         }
 373
 374         SymbolExportLevel::C
 375     } else {
 376         SymbolExportLevel::Rust
 377     }
 378 }