src/librustc_trans/back/symbol_export.rs

   1 // Copyright 2016 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use context::SharedCrateContext;
  12 use monomorphize::Instance;
  13 use symbol_map::SymbolMap;
  14 use back::symbol_names::symbol_name;
  15 use util::nodemap::FxHashMap;
  16 use rustc::hir::def_id::{DefId, CrateNum, LOCAL_CRATE};
  17 use rustc::session::config;
  18 use syntax::attr;
  19 use trans_item::TransItem;
  20
  21 /// The SymbolExportLevel of a symbols specifies from which kinds of crates
  22 /// the symbol will be exported. `C` symbols will be exported from any
  23 /// kind of crate, including cdylibs which export very few things.
  24 /// `Rust` will only be exported if the crate produced is a Rust
  25 /// dylib.
  26 #[derive(Eq, PartialEq, Debug, Copy, Clone)]
  27 pub enum SymbolExportLevel {
  28     C,
  29     Rust,
  30 }
  31
  32 /// The set of symbols exported from each crate in the crate graph.
  33 pub struct ExportedSymbols {
  34     exports: FxHashMap<CrateNum, Vec<(String, SymbolExportLevel)>>,
  35 }
  36
  37 impl ExportedSymbols {
  38
  39     pub fn empty() -> ExportedSymbols {
  40         ExportedSymbols {
  41             exports: FxHashMap(),
  42         }
  43     }
  44
  45     pub fn compute_from<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
  46                                   symbol_map: &SymbolMap<'tcx>)
  47                                   -> ExportedSymbols {
  48         let mut local_crate: Vec<_> = scx
  49             .exported_symbols()
  50             .iter()
  51             .map(|&node_id| {
  52                 scx.tcx().hir.local_def_id(node_id)
  53             })
  54             .map(|def_id| {
  55                 let name = symbol_for_def_id(scx, def_id, symbol_map);
  56                 let export_level = export_level(scx, def_id);
  57                 debug!("EXPORTED SYMBOL (local): {} ({:?})", name, export_level);
  58                 (name, export_level)
  59             })
  60             .collect();
  61
  62         if scx.sess().entry_fn.borrow().is_some() {
  63             local_crate.push(("main".to_string(), SymbolExportLevel::C));
  64         }
  65
  66         if let Some(id) = scx.sess().derive_registrar_fn.get() {
  67             let svh = &scx.link_meta().crate_hash;
  68             let def_id = scx.tcx().hir.local_def_id(id);
  69             let idx = def_id.index;
  70             let registrar = scx.sess().generate_derive_registrar_symbol(svh, idx);
  71             local_crate.push((registrar, SymbolExportLevel::C));
  72         }
  73
  74         if scx.sess().crate_types.borrow().contains(&config::CrateTypeDylib) {
  75             local_crate.push((scx.metadata_symbol_name(),
  76                               SymbolExportLevel::Rust));
  77         }
  78
  79         let mut exports = FxHashMap();
  80         exports.insert(LOCAL_CRATE, local_crate);
  81
  82         for cnum in scx.sess().cstore.crates() {
  83             debug_assert!(cnum != LOCAL_CRATE);
  84
  85             // If this crate is a plugin and/or a custom derive crate, then
  86             // we're not even going to link those in so we skip those crates.
  87             if scx.sess().cstore.plugin_registrar_fn(cnum).is_some() ||
  88                scx.sess().cstore.derive_registrar_fn(cnum).is_some() {
  89                 continue;
  90             }
  91
  92             // Check to see if this crate is a "special runtime crate". These
  93             // crates, implementation details of the standard library, typically
  94             // have a bunch of `pub extern` and `#[no_mangle]` functions as the
  95             // ABI between them. We don't want their symbols to have a `C`
  96             // export level, however, as they're just implementation details.
  97             // Down below we'll hardwire all of the symbols to the `Rust` export
  98             // level instead.
  99             let special_runtime_crate =
 100                 scx.sess().cstore.is_allocator(cnum) ||
 101                 scx.sess().cstore.is_panic_runtime(cnum) ||
 102                 scx.sess().cstore.is_compiler_builtins(cnum);
 103
 104             let crate_exports = scx
 105                 .sess()
 106                 .cstore
 107                 .exported_symbols(cnum)
 108                 .iter()
 109                 .map(|&def_id| {
 110                     let name = symbol_name(Instance::mono(scx.tcx(), def_id), scx);
 111                     let export_level = if special_runtime_crate {
 112                         // We can probably do better here by just ensuring that
 113                         // it has hidden visibility rather than public
 114                         // visibility, as this is primarily here to ensure it's
 115                         // not stripped during LTO.
 116                         //
 117                         // In general though we won't link right if these
 118                         // symbols are stripped, and LTO currently strips them.
 119                         if name == "rust_eh_personality" ||
 120                            name == "rust_eh_register_frames" ||
 121                            name == "rust_eh_unregister_frames" {
 122                             SymbolExportLevel::C
 123                         } else {
 124                             SymbolExportLevel::Rust
 125                         }
 126                     } else {
 127                         export_level(scx, def_id)
 128                     };
 129                     debug!("EXPORTED SYMBOL (re-export): {} ({:?})", name, export_level);
 130                     (name, export_level)
 131                 })
 132                 .collect();
 133
 134             exports.insert(cnum, crate_exports);
 135         }
 136
 137         return ExportedSymbols {
 138             exports: exports
 139         };
 140
 141         fn export_level(scx: &SharedCrateContext,
 142                         sym_def_id: DefId)
 143                         -> SymbolExportLevel {
 144             let attrs = scx.tcx().get_attrs(sym_def_id);
 145             if attr::contains_extern_indicator(scx.sess().diagnostic(), &attrs) {
 146                 SymbolExportLevel::C
 147             } else {
 148                 SymbolExportLevel::Rust
 149             }
 150         }
 151     }
 152
 153     pub fn exported_symbols(&self,
 154                             cnum: CrateNum)
 155                             -> &[(String, SymbolExportLevel)] {
 156         match self.exports.get(&cnum) {
 157             Some(exports) => &exports[..],
 158             None => &[]
 159         }
 160     }
 161
 162     pub fn for_each_exported_symbol<F>(&self,
 163                                        cnum: CrateNum,
 164                                        export_threshold: SymbolExportLevel,
 165                                        mut f: F)
 166         where F: FnMut(&str, SymbolExportLevel)
 167     {
 168         for &(ref name, export_level) in self.exported_symbols(cnum) {
 169             if is_below_threshold(export_level, export_threshold) {
 170                 f(&name[..], export_level)
 171             }
 172         }
 173     }
 174 }
 175
 176 pub fn crate_export_threshold(crate_type: config::CrateType)
 177                                      -> SymbolExportLevel {
 178     match crate_type {
 179         config::CrateTypeExecutable |
 180         config::CrateTypeStaticlib  |
 181         config::CrateTypeProcMacro  |
 182         config::CrateTypeCdylib     => SymbolExportLevel::C,
 183         config::CrateTypeRlib       |
 184         config::CrateTypeDylib      => SymbolExportLevel::Rust,
 185     }
 186 }
 187
 188 pub fn crates_export_threshold(crate_types: &[config::CrateType])
 189                                       -> SymbolExportLevel {
 190     if crate_types.iter().any(|&crate_type| {
 191         crate_export_threshold(crate_type) == SymbolExportLevel::Rust
 192     }) {
 193         SymbolExportLevel::Rust
 194     } else {
 195         SymbolExportLevel::C
 196     }
 197 }
 198
 199 pub fn is_below_threshold(level: SymbolExportLevel,
 200                           threshold: SymbolExportLevel)
 201                           -> bool {
 202     if threshold == SymbolExportLevel::Rust {
 203         // We export everything from Rust dylibs
 204         true
 205     } else {
 206         level == SymbolExportLevel::C
 207     }
 208 }
 209
 210 fn symbol_for_def_id<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
 211                                def_id: DefId,
 212                                symbol_map: &SymbolMap<'tcx>)
 213                                -> String {
 214     // Just try to look things up in the symbol map. If nothing's there, we
 215     // recompute.
 216     if let Some(node_id) = scx.tcx().hir.as_local_node_id(def_id) {
 217         if let Some(sym) = symbol_map.get(TransItem::Static(node_id)) {
 218             return sym.to_owned();
 219         }
 220     }
 221
 222     let instance = Instance::mono(scx.tcx(), def_id);
 223
 224     symbol_map.get(TransItem::Fn(instance))
 225               .map(str::to_owned)
 226               .unwrap_or_else(|| symbol_name(instance, scx))
 227 }