1 //===- IRSymtab.cpp - implementation of IR symbol tables ------------------===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 9 #include "llvm/Object/IRSymtab.h" 10 #include "llvm/ADT/ArrayRef.h" 11 #include "llvm/ADT/DenseMap.h" 12 #include "llvm/ADT/SmallPtrSet.h" 13 #include "llvm/ADT/SmallString.h" 14 #include "llvm/ADT/SmallVector.h" 15 #include "llvm/ADT/StringRef.h" 16 #include "llvm/ADT/Triple.h" 17 #include "llvm/Config/llvm-config.h" 18 #include "llvm/IR/Comdat.h" 19 #include "llvm/IR/DataLayout.h" 20 #include "llvm/IR/GlobalAlias.h" 21 #include "llvm/IR/GlobalObject.h" 22 #include "llvm/IR/Mangler.h" 23 #include "llvm/IR/Metadata.h" 24 #include "llvm/IR/Module.h" 25 #include "llvm/Bitcode/BitcodeReader.h" 26 #include "llvm/MC/StringTableBuilder.h" 27 #include "llvm/Object/IRObjectFile.h" 28 #include "llvm/Object/ModuleSymbolTable.h" 29 #include "llvm/Object/SymbolicFile.h" 30 #include "llvm/Support/Allocator.h" 31 #include "llvm/Support/Casting.h" 32 #include "llvm/Support/Error.h" 33 #include "llvm/Support/StringSaver.h" 34 #include "llvm/Support/VCSRevision.h" 35 #include "llvm/Support/raw_ostream.h" 36 #include <cassert> 37 #include <string> 38 #include <utility> 39 #include <vector> 40 41 using namespace llvm; 42 using namespace irsymtab; 43 44 static const char *LibcallRoutineNames[] = { 45 #define HANDLE_LIBCALL(code, name) name, 46 #include "llvm/IR/RuntimeLibcalls.def" 47 #undef HANDLE_LIBCALL 48 }; 49 50 namespace { 51 52 const char *getExpectedProducerName() { 53 static char DefaultName[] = LLVM_VERSION_STRING 54 #ifdef LLVM_REVISION 55 " " LLVM_REVISION 56 #endif 57 ; 58 // Allows for testing of the irsymtab writer and upgrade mechanism. This 59 // environment variable should not be set by users. 60 if (char *OverrideName = getenv("LLVM_OVERRIDE_PRODUCER")) 61 return OverrideName; 62 return DefaultName; 63 } 64 65 const char *kExpectedProducerName = getExpectedProducerName(); 66 67 /// Stores the temporary state that is required to build an IR symbol table. 68 struct Builder { 69 SmallVector<char, 0> &Symtab; 70 StringTableBuilder &StrtabBuilder; 71 StringSaver Saver; 72 73 // This ctor initializes a StringSaver using the passed in BumpPtrAllocator. 74 // The StringTableBuilder does not create a copy of any strings added to it, 75 // so this provides somewhere to store any strings that we create. 76 Builder(SmallVector<char, 0> &Symtab, StringTableBuilder &StrtabBuilder, 77 BumpPtrAllocator &Alloc) 78 : Symtab(Symtab), StrtabBuilder(StrtabBuilder), Saver(Alloc) {} 79 80 DenseMap<const Comdat *, int> ComdatMap; 81 Mangler Mang; 82 Triple TT; 83 84 std::vector<storage::Comdat> Comdats; 85 std::vector<storage::Module> Mods; 86 std::vector<storage::Symbol> Syms; 87 std::vector<storage::Uncommon> Uncommons; 88 89 std::string COFFLinkerOpts; 90 raw_string_ostream COFFLinkerOptsOS{COFFLinkerOpts}; 91 92 std::vector<storage::Str> DependentLibraries; 93 94 void setStr(storage::Str &S, StringRef Value) { 95 S.Offset = StrtabBuilder.add(Value); 96 S.Size = Value.size(); 97 } 98 99 template <typename T> 100 void writeRange(storage::Range<T> &R, const std::vector<T> &Objs) { 101 R.Offset = Symtab.size(); 102 R.Size = Objs.size(); 103 Symtab.insert(Symtab.end(), reinterpret_cast<const char *>(Objs.data()), 104 reinterpret_cast<const char *>(Objs.data() + Objs.size())); 105 } 106 107 Expected<int> getComdatIndex(const Comdat *C, const Module *M); 108 109 Error addModule(Module *M); 110 Error addSymbol(const ModuleSymbolTable &Msymtab, 111 const SmallPtrSet<GlobalValue *, 4> &Used, 112 ModuleSymbolTable::Symbol Sym); 113 114 Error build(ArrayRef<Module *> Mods); 115 }; 116 117 Error Builder::addModule(Module *M) { 118 if (M->getDataLayoutStr().empty()) 119 return make_error<StringError>("input module has no datalayout", 120 inconvertibleErrorCode()); 121 122 // Symbols in the llvm.used list will get the FB_Used bit and will not be 123 // internalized. We do this for llvm.compiler.used as well: 124 // 125 // IR symbol table tracks module-level asm symbol references but not inline 126 // asm. A symbol only referenced by inline asm is not in the IR symbol table, 127 // so we may not know that the definition (in another translation unit) is 128 // referenced. That definition may have __attribute__((used)) (which lowers to 129 // llvm.compiler.used on ELF targets) to communicate to the compiler that it 130 // may be used by inline asm. The usage is perfectly fine, so we treat 131 // llvm.compiler.used conservatively as llvm.used to work around our own 132 // limitation. 133 SmallVector<GlobalValue *, 4> UsedV; 134 collectUsedGlobalVariables(*M, UsedV, /*CompilerUsed=*/false); 135 collectUsedGlobalVariables(*M, UsedV, /*CompilerUsed=*/true); 136 SmallPtrSet<GlobalValue *, 4> Used(UsedV.begin(), UsedV.end()); 137 138 ModuleSymbolTable Msymtab; 139 Msymtab.addModule(M); 140 141 storage::Module Mod; 142 Mod.Begin = Syms.size(); 143 Mod.End = Syms.size() + Msymtab.symbols().size(); 144 Mod.UncBegin = Uncommons.size(); 145 Mods.push_back(Mod); 146 147 if (TT.isOSBinFormatCOFF()) { 148 if (auto E = M->materializeMetadata()) 149 return E; 150 if (NamedMDNode *LinkerOptions = 151 M->getNamedMetadata("llvm.linker.options")) { 152 for (MDNode *MDOptions : LinkerOptions->operands()) 153 for (const MDOperand &MDOption : cast<MDNode>(MDOptions)->operands()) 154 COFFLinkerOptsOS << " " << cast<MDString>(MDOption)->getString(); 155 } 156 } 157 158 if (TT.isOSBinFormatELF()) { 159 if (auto E = M->materializeMetadata()) 160 return E; 161 if (NamedMDNode *N = M->getNamedMetadata("llvm.dependent-libraries")) { 162 for (MDNode *MDOptions : N->operands()) { 163 const auto OperandStr = 164 cast<MDString>(cast<MDNode>(MDOptions)->getOperand(0))->getString(); 165 storage::Str Specifier; 166 setStr(Specifier, OperandStr); 167 DependentLibraries.emplace_back(Specifier); 168 } 169 } 170 } 171 172 for (ModuleSymbolTable::Symbol Msym : Msymtab.symbols()) 173 if (Error Err = addSymbol(Msymtab, Used, Msym)) 174 return Err; 175 176 return Error::success(); 177 } 178 179 Expected<int> Builder::getComdatIndex(const Comdat *C, const Module *M) { 180 auto P = ComdatMap.insert(std::make_pair(C, Comdats.size())); 181 if (P.second) { 182 std::string Name; 183 if (TT.isOSBinFormatCOFF()) { 184 const GlobalValue *GV = M->getNamedValue(C->getName()); 185 if (!GV) 186 return make_error<StringError>("Could not find leader", 187 inconvertibleErrorCode()); 188 // Internal leaders do not affect symbol resolution, therefore they do not 189 // appear in the symbol table. 190 if (GV->hasLocalLinkage()) { 191 P.first->second = -1; 192 return -1; 193 } 194 llvm::raw_string_ostream OS(Name); 195 Mang.getNameWithPrefix(OS, GV, false); 196 } else { 197 Name = std::string(C->getName()); 198 } 199 200 storage::Comdat Comdat; 201 setStr(Comdat.Name, Saver.save(Name)); 202 Comdat.SelectionKind = C->getSelectionKind(); 203 Comdats.push_back(Comdat); 204 } 205 206 return P.first->second; 207 } 208 209 Error Builder::addSymbol(const ModuleSymbolTable &Msymtab, 210 const SmallPtrSet<GlobalValue *, 4> &Used, 211 ModuleSymbolTable::Symbol Msym) { 212 Syms.emplace_back(); 213 storage::Symbol &Sym = Syms.back(); 214 Sym = {}; 215 216 storage::Uncommon *Unc = nullptr; 217 auto Uncommon = [&]() -> storage::Uncommon & { 218 if (Unc) 219 return *Unc; 220 Sym.Flags |= 1 << storage::Symbol::FB_has_uncommon; 221 Uncommons.emplace_back(); 222 Unc = &Uncommons.back(); 223 *Unc = {}; 224 setStr(Unc->COFFWeakExternFallbackName, ""); 225 setStr(Unc->SectionName, ""); 226 return *Unc; 227 }; 228 229 SmallString<64> Name; 230 { 231 raw_svector_ostream OS(Name); 232 Msymtab.printSymbolName(OS, Msym); 233 } 234 setStr(Sym.Name, Saver.save(Name.str())); 235 236 auto Flags = Msymtab.getSymbolFlags(Msym); 237 if (Flags & object::BasicSymbolRef::SF_Undefined) 238 Sym.Flags |= 1 << storage::Symbol::FB_undefined; 239 if (Flags & object::BasicSymbolRef::SF_Weak) 240 Sym.Flags |= 1 << storage::Symbol::FB_weak; 241 if (Flags & object::BasicSymbolRef::SF_Common) 242 Sym.Flags |= 1 << storage::Symbol::FB_common; 243 if (Flags & object::BasicSymbolRef::SF_Indirect) 244 Sym.Flags |= 1 << storage::Symbol::FB_indirect; 245 if (Flags & object::BasicSymbolRef::SF_Global) 246 Sym.Flags |= 1 << storage::Symbol::FB_global; 247 if (Flags & object::BasicSymbolRef::SF_FormatSpecific) 248 Sym.Flags |= 1 << storage::Symbol::FB_format_specific; 249 if (Flags & object::BasicSymbolRef::SF_Executable) 250 Sym.Flags |= 1 << storage::Symbol::FB_executable; 251 252 Sym.ComdatIndex = -1; 253 auto *GV = Msym.dyn_cast<GlobalValue *>(); 254 if (!GV) { 255 // Undefined module asm symbols act as GC roots and are implicitly used. 256 if (Flags & object::BasicSymbolRef::SF_Undefined) 257 Sym.Flags |= 1 << storage::Symbol::FB_used; 258 setStr(Sym.IRName, ""); 259 return Error::success(); 260 } 261 262 setStr(Sym.IRName, GV->getName()); 263 264 bool IsBuiltinFunc = llvm::is_contained(LibcallRoutineNames, GV->getName()); 265 266 if (Used.count(GV) || IsBuiltinFunc) 267 Sym.Flags |= 1 << storage::Symbol::FB_used; 268 if (GV->isThreadLocal()) 269 Sym.Flags |= 1 << storage::Symbol::FB_tls; 270 if (GV->hasGlobalUnnamedAddr()) 271 Sym.Flags |= 1 << storage::Symbol::FB_unnamed_addr; 272 if (GV->canBeOmittedFromSymbolTable()) 273 Sym.Flags |= 1 << storage::Symbol::FB_may_omit; 274 Sym.Flags |= unsigned(GV->getVisibility()) << storage::Symbol::FB_visibility; 275 276 if (Flags & object::BasicSymbolRef::SF_Common) { 277 auto *GVar = dyn_cast<GlobalVariable>(GV); 278 if (!GVar) 279 return make_error<StringError>("Only variables can have common linkage!", 280 inconvertibleErrorCode()); 281 Uncommon().CommonSize = 282 GV->getParent()->getDataLayout().getTypeAllocSize(GV->getValueType()); 283 Uncommon().CommonAlign = GVar->getAlignment(); 284 } 285 286 const GlobalObject *Base = GV->getBaseObject(); 287 if (!Base) 288 return make_error<StringError>("Unable to determine comdat of alias!", 289 inconvertibleErrorCode()); 290 if (const Comdat *C = Base->getComdat()) { 291 Expected<int> ComdatIndexOrErr = getComdatIndex(C, GV->getParent()); 292 if (!ComdatIndexOrErr) 293 return ComdatIndexOrErr.takeError(); 294 Sym.ComdatIndex = *ComdatIndexOrErr; 295 } 296 297 if (TT.isOSBinFormatCOFF()) { 298 emitLinkerFlagsForGlobalCOFF(COFFLinkerOptsOS, GV, TT, Mang); 299 300 if ((Flags & object::BasicSymbolRef::SF_Weak) && 301 (Flags & object::BasicSymbolRef::SF_Indirect)) { 302 auto *Fallback = dyn_cast<GlobalValue>( 303 cast<GlobalAlias>(GV)->getAliasee()->stripPointerCasts()); 304 if (!Fallback) 305 return make_error<StringError>("Invalid weak external", 306 inconvertibleErrorCode()); 307 std::string FallbackName; 308 raw_string_ostream OS(FallbackName); 309 Msymtab.printSymbolName(OS, Fallback); 310 OS.flush(); 311 setStr(Uncommon().COFFWeakExternFallbackName, Saver.save(FallbackName)); 312 } 313 } 314 315 if (!Base->getSection().empty()) 316 setStr(Uncommon().SectionName, Saver.save(Base->getSection())); 317 318 return Error::success(); 319 } 320 321 Error Builder::build(ArrayRef<Module *> IRMods) { 322 storage::Header Hdr; 323 324 assert(!IRMods.empty()); 325 Hdr.Version = storage::Header::kCurrentVersion; 326 setStr(Hdr.Producer, kExpectedProducerName); 327 setStr(Hdr.TargetTriple, IRMods[0]->getTargetTriple()); 328 setStr(Hdr.SourceFileName, IRMods[0]->getSourceFileName()); 329 TT = Triple(IRMods[0]->getTargetTriple()); 330 331 for (auto *M : IRMods) 332 if (Error Err = addModule(M)) 333 return Err; 334 335 COFFLinkerOptsOS.flush(); 336 setStr(Hdr.COFFLinkerOpts, Saver.save(COFFLinkerOpts)); 337 338 // We are about to fill in the header's range fields, so reserve space for it 339 // and copy it in afterwards. 340 Symtab.resize(sizeof(storage::Header)); 341 writeRange(Hdr.Modules, Mods); 342 writeRange(Hdr.Comdats, Comdats); 343 writeRange(Hdr.Symbols, Syms); 344 writeRange(Hdr.Uncommons, Uncommons); 345 writeRange(Hdr.DependentLibraries, DependentLibraries); 346 *reinterpret_cast<storage::Header *>(Symtab.data()) = Hdr; 347 return Error::success(); 348 } 349 350 } // end anonymous namespace 351 352 Error irsymtab::build(ArrayRef<Module *> Mods, SmallVector<char, 0> &Symtab, 353 StringTableBuilder &StrtabBuilder, 354 BumpPtrAllocator &Alloc) { 355 return Builder(Symtab, StrtabBuilder, Alloc).build(Mods); 356 } 357 358 // Upgrade a vector of bitcode modules created by an old version of LLVM by 359 // creating an irsymtab for them in the current format. 360 static Expected<FileContents> upgrade(ArrayRef<BitcodeModule> BMs) { 361 FileContents FC; 362 363 LLVMContext Ctx; 364 std::vector<Module *> Mods; 365 std::vector<std::unique_ptr<Module>> OwnedMods; 366 for (auto BM : BMs) { 367 Expected<std::unique_ptr<Module>> MOrErr = 368 BM.getLazyModule(Ctx, /*ShouldLazyLoadMetadata*/ true, 369 /*IsImporting*/ false); 370 if (!MOrErr) 371 return MOrErr.takeError(); 372 373 Mods.push_back(MOrErr->get()); 374 OwnedMods.push_back(std::move(*MOrErr)); 375 } 376 377 StringTableBuilder StrtabBuilder(StringTableBuilder::RAW); 378 BumpPtrAllocator Alloc; 379 if (Error E = build(Mods, FC.Symtab, StrtabBuilder, Alloc)) 380 return std::move(E); 381 382 StrtabBuilder.finalizeInOrder(); 383 FC.Strtab.resize(StrtabBuilder.getSize()); 384 StrtabBuilder.write((uint8_t *)FC.Strtab.data()); 385 386 FC.TheReader = {{FC.Symtab.data(), FC.Symtab.size()}, 387 {FC.Strtab.data(), FC.Strtab.size()}}; 388 return std::move(FC); 389 } 390 391 Expected<FileContents> irsymtab::readBitcode(const BitcodeFileContents &BFC) { 392 if (BFC.Mods.empty()) 393 return make_error<StringError>("Bitcode file does not contain any modules", 394 inconvertibleErrorCode()); 395 396 if (BFC.StrtabForSymtab.empty() || 397 BFC.Symtab.size() < sizeof(storage::Header)) 398 return upgrade(BFC.Mods); 399 400 // We cannot use the regular reader to read the version and producer, because 401 // it will expect the header to be in the current format. The only thing we 402 // can rely on is that the version and producer will be present as the first 403 // struct elements. 404 auto *Hdr = reinterpret_cast<const storage::Header *>(BFC.Symtab.data()); 405 unsigned Version = Hdr->Version; 406 StringRef Producer = Hdr->Producer.get(BFC.StrtabForSymtab); 407 if (Version != storage::Header::kCurrentVersion || 408 Producer != kExpectedProducerName) 409 return upgrade(BFC.Mods); 410 411 FileContents FC; 412 FC.TheReader = {{BFC.Symtab.data(), BFC.Symtab.size()}, 413 {BFC.StrtabForSymtab.data(), BFC.StrtabForSymtab.size()}}; 414 415 // Finally, make sure that the number of modules in the symbol table matches 416 // the number of modules in the bitcode file. If they differ, it may mean that 417 // the bitcode file was created by binary concatenation, so we need to create 418 // a new symbol table from scratch. 419 if (FC.TheReader.getNumModules() != BFC.Mods.size()) 420 return upgrade(std::move(BFC.Mods)); 421 422 return std::move(FC); 423 } 424