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/Bitcode/BitcodeReader.h" 18 #include "llvm/Config/llvm-config.h" 19 #include "llvm/IR/Comdat.h" 20 #include "llvm/IR/DataLayout.h" 21 #include "llvm/IR/GlobalAlias.h" 22 #include "llvm/IR/GlobalObject.h" 23 #include "llvm/IR/Mangler.h" 24 #include "llvm/IR/Metadata.h" 25 #include "llvm/IR/Module.h" 26 #include "llvm/MC/StringTableBuilder.h" 27 #include "llvm/Object/ModuleSymbolTable.h" 28 #include "llvm/Object/SymbolicFile.h" 29 #include "llvm/Support/Allocator.h" 30 #include "llvm/Support/Casting.h" 31 #include "llvm/Support/CommandLine.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 cl::opt<bool> DisableBitcodeVersionUpgrade( 45 "disable-bitcode-version-upgrade", cl::init(false), cl::Hidden, 46 cl::desc("Disable automatic bitcode upgrade for version mismatch")); 47 48 static const char *PreservedSymbols[] = { 49 #define HANDLE_LIBCALL(code, name) name, 50 #include "llvm/IR/RuntimeLibcalls.def" 51 #undef HANDLE_LIBCALL 52 // There are global variables, so put it here instead of in 53 // RuntimeLibcalls.def. 54 // TODO: Are there similar such variables? 55 "__ssp_canary_word", 56 "__stack_chk_guard", 57 }; 58 59 namespace { 60 61 const char *getExpectedProducerName() { 62 static char DefaultName[] = LLVM_VERSION_STRING 63 #ifdef LLVM_REVISION 64 " " LLVM_REVISION 65 #endif 66 ; 67 // Allows for testing of the irsymtab writer and upgrade mechanism. This 68 // environment variable should not be set by users. 69 if (char *OverrideName = getenv("LLVM_OVERRIDE_PRODUCER")) 70 return OverrideName; 71 return DefaultName; 72 } 73 74 const char *kExpectedProducerName = getExpectedProducerName(); 75 76 /// Stores the temporary state that is required to build an IR symbol table. 77 struct Builder { 78 SmallVector<char, 0> &Symtab; 79 StringTableBuilder &StrtabBuilder; 80 StringSaver Saver; 81 82 // This ctor initializes a StringSaver using the passed in BumpPtrAllocator. 83 // The StringTableBuilder does not create a copy of any strings added to it, 84 // so this provides somewhere to store any strings that we create. 85 Builder(SmallVector<char, 0> &Symtab, StringTableBuilder &StrtabBuilder, 86 BumpPtrAllocator &Alloc) 87 : Symtab(Symtab), StrtabBuilder(StrtabBuilder), Saver(Alloc) {} 88 89 DenseMap<const Comdat *, int> ComdatMap; 90 Mangler Mang; 91 Triple TT; 92 93 std::vector<storage::Comdat> Comdats; 94 std::vector<storage::Module> Mods; 95 std::vector<storage::Symbol> Syms; 96 std::vector<storage::Uncommon> Uncommons; 97 98 std::string COFFLinkerOpts; 99 raw_string_ostream COFFLinkerOptsOS{COFFLinkerOpts}; 100 101 std::vector<storage::Str> DependentLibraries; 102 103 void setStr(storage::Str &S, StringRef Value) { 104 S.Offset = StrtabBuilder.add(Value); 105 S.Size = Value.size(); 106 } 107 108 template <typename T> 109 void writeRange(storage::Range<T> &R, const std::vector<T> &Objs) { 110 R.Offset = Symtab.size(); 111 R.Size = Objs.size(); 112 Symtab.insert(Symtab.end(), reinterpret_cast<const char *>(Objs.data()), 113 reinterpret_cast<const char *>(Objs.data() + Objs.size())); 114 } 115 116 Expected<int> getComdatIndex(const Comdat *C, const Module *M); 117 118 Error addModule(Module *M); 119 Error addSymbol(const ModuleSymbolTable &Msymtab, 120 const SmallPtrSet<GlobalValue *, 4> &Used, 121 ModuleSymbolTable::Symbol Sym); 122 123 Error build(ArrayRef<Module *> Mods); 124 }; 125 126 Error Builder::addModule(Module *M) { 127 if (M->getDataLayoutStr().empty()) 128 return make_error<StringError>("input module has no datalayout", 129 inconvertibleErrorCode()); 130 131 // Symbols in the llvm.used list will get the FB_Used bit and will not be 132 // internalized. We do this for llvm.compiler.used as well: 133 // 134 // IR symbol table tracks module-level asm symbol references but not inline 135 // asm. A symbol only referenced by inline asm is not in the IR symbol table, 136 // so we may not know that the definition (in another translation unit) is 137 // referenced. That definition may have __attribute__((used)) (which lowers to 138 // llvm.compiler.used on ELF targets) to communicate to the compiler that it 139 // may be used by inline asm. The usage is perfectly fine, so we treat 140 // llvm.compiler.used conservatively as llvm.used to work around our own 141 // limitation. 142 SmallVector<GlobalValue *, 4> UsedV; 143 collectUsedGlobalVariables(*M, UsedV, /*CompilerUsed=*/false); 144 collectUsedGlobalVariables(*M, UsedV, /*CompilerUsed=*/true); 145 SmallPtrSet<GlobalValue *, 4> Used(UsedV.begin(), UsedV.end()); 146 147 ModuleSymbolTable Msymtab; 148 Msymtab.addModule(M); 149 150 storage::Module Mod; 151 Mod.Begin = Syms.size(); 152 Mod.End = Syms.size() + Msymtab.symbols().size(); 153 Mod.UncBegin = Uncommons.size(); 154 Mods.push_back(Mod); 155 156 if (TT.isOSBinFormatCOFF()) { 157 if (auto E = M->materializeMetadata()) 158 return E; 159 if (NamedMDNode *LinkerOptions = 160 M->getNamedMetadata("llvm.linker.options")) { 161 for (MDNode *MDOptions : LinkerOptions->operands()) 162 for (const MDOperand &MDOption : cast<MDNode>(MDOptions)->operands()) 163 COFFLinkerOptsOS << " " << cast<MDString>(MDOption)->getString(); 164 } 165 } 166 167 if (TT.isOSBinFormatELF()) { 168 if (auto E = M->materializeMetadata()) 169 return E; 170 if (NamedMDNode *N = M->getNamedMetadata("llvm.dependent-libraries")) { 171 for (MDNode *MDOptions : N->operands()) { 172 const auto OperandStr = 173 cast<MDString>(cast<MDNode>(MDOptions)->getOperand(0))->getString(); 174 storage::Str Specifier; 175 setStr(Specifier, OperandStr); 176 DependentLibraries.emplace_back(Specifier); 177 } 178 } 179 } 180 181 for (ModuleSymbolTable::Symbol Msym : Msymtab.symbols()) 182 if (Error Err = addSymbol(Msymtab, Used, Msym)) 183 return Err; 184 185 return Error::success(); 186 } 187 188 Expected<int> Builder::getComdatIndex(const Comdat *C, const Module *M) { 189 auto P = ComdatMap.insert(std::make_pair(C, Comdats.size())); 190 if (P.second) { 191 std::string Name; 192 if (TT.isOSBinFormatCOFF()) { 193 const GlobalValue *GV = M->getNamedValue(C->getName()); 194 if (!GV) 195 return make_error<StringError>("Could not find leader", 196 inconvertibleErrorCode()); 197 // Internal leaders do not affect symbol resolution, therefore they do not 198 // appear in the symbol table. 199 if (GV->hasLocalLinkage()) { 200 P.first->second = -1; 201 return -1; 202 } 203 llvm::raw_string_ostream OS(Name); 204 Mang.getNameWithPrefix(OS, GV, false); 205 } else { 206 Name = std::string(C->getName()); 207 } 208 209 storage::Comdat Comdat; 210 setStr(Comdat.Name, Saver.save(Name)); 211 Comdat.SelectionKind = C->getSelectionKind(); 212 Comdats.push_back(Comdat); 213 } 214 215 return P.first->second; 216 } 217 218 Error Builder::addSymbol(const ModuleSymbolTable &Msymtab, 219 const SmallPtrSet<GlobalValue *, 4> &Used, 220 ModuleSymbolTable::Symbol Msym) { 221 Syms.emplace_back(); 222 storage::Symbol &Sym = Syms.back(); 223 Sym = {}; 224 225 storage::Uncommon *Unc = nullptr; 226 auto Uncommon = [&]() -> storage::Uncommon & { 227 if (Unc) 228 return *Unc; 229 Sym.Flags |= 1 << storage::Symbol::FB_has_uncommon; 230 Uncommons.emplace_back(); 231 Unc = &Uncommons.back(); 232 *Unc = {}; 233 setStr(Unc->COFFWeakExternFallbackName, ""); 234 setStr(Unc->SectionName, ""); 235 return *Unc; 236 }; 237 238 SmallString<64> Name; 239 { 240 raw_svector_ostream OS(Name); 241 Msymtab.printSymbolName(OS, Msym); 242 } 243 setStr(Sym.Name, Saver.save(Name.str())); 244 245 auto Flags = Msymtab.getSymbolFlags(Msym); 246 if (Flags & object::BasicSymbolRef::SF_Undefined) 247 Sym.Flags |= 1 << storage::Symbol::FB_undefined; 248 if (Flags & object::BasicSymbolRef::SF_Weak) 249 Sym.Flags |= 1 << storage::Symbol::FB_weak; 250 if (Flags & object::BasicSymbolRef::SF_Common) 251 Sym.Flags |= 1 << storage::Symbol::FB_common; 252 if (Flags & object::BasicSymbolRef::SF_Indirect) 253 Sym.Flags |= 1 << storage::Symbol::FB_indirect; 254 if (Flags & object::BasicSymbolRef::SF_Global) 255 Sym.Flags |= 1 << storage::Symbol::FB_global; 256 if (Flags & object::BasicSymbolRef::SF_FormatSpecific) 257 Sym.Flags |= 1 << storage::Symbol::FB_format_specific; 258 if (Flags & object::BasicSymbolRef::SF_Executable) 259 Sym.Flags |= 1 << storage::Symbol::FB_executable; 260 261 Sym.ComdatIndex = -1; 262 auto *GV = Msym.dyn_cast<GlobalValue *>(); 263 if (!GV) { 264 // Undefined module asm symbols act as GC roots and are implicitly used. 265 if (Flags & object::BasicSymbolRef::SF_Undefined) 266 Sym.Flags |= 1 << storage::Symbol::FB_used; 267 setStr(Sym.IRName, ""); 268 return Error::success(); 269 } 270 271 setStr(Sym.IRName, GV->getName()); 272 273 bool IsPreservedSymbol = llvm::is_contained(PreservedSymbols, GV->getName()); 274 275 if (Used.count(GV) || IsPreservedSymbol) 276 Sym.Flags |= 1 << storage::Symbol::FB_used; 277 if (GV->isThreadLocal()) 278 Sym.Flags |= 1 << storage::Symbol::FB_tls; 279 if (GV->hasGlobalUnnamedAddr()) 280 Sym.Flags |= 1 << storage::Symbol::FB_unnamed_addr; 281 if (GV->canBeOmittedFromSymbolTable()) 282 Sym.Flags |= 1 << storage::Symbol::FB_may_omit; 283 Sym.Flags |= unsigned(GV->getVisibility()) << storage::Symbol::FB_visibility; 284 285 if (Flags & object::BasicSymbolRef::SF_Common) { 286 auto *GVar = dyn_cast<GlobalVariable>(GV); 287 if (!GVar) 288 return make_error<StringError>("Only variables can have common linkage!", 289 inconvertibleErrorCode()); 290 Uncommon().CommonSize = 291 GV->getParent()->getDataLayout().getTypeAllocSize(GV->getValueType()); 292 Uncommon().CommonAlign = GVar->getAlign() ? GVar->getAlign()->value() : 0; 293 } 294 295 const GlobalObject *GO = GV->getAliaseeObject(); 296 if (!GO) { 297 if (isa<GlobalIFunc>(GV)) 298 GO = cast<GlobalIFunc>(GV)->getResolverFunction(); 299 if (!GO) 300 return make_error<StringError>("Unable to determine comdat of alias!", 301 inconvertibleErrorCode()); 302 } 303 if (const Comdat *C = GO->getComdat()) { 304 Expected<int> ComdatIndexOrErr = getComdatIndex(C, GV->getParent()); 305 if (!ComdatIndexOrErr) 306 return ComdatIndexOrErr.takeError(); 307 Sym.ComdatIndex = *ComdatIndexOrErr; 308 } 309 310 if (TT.isOSBinFormatCOFF()) { 311 emitLinkerFlagsForGlobalCOFF(COFFLinkerOptsOS, GV, TT, Mang); 312 313 if ((Flags & object::BasicSymbolRef::SF_Weak) && 314 (Flags & object::BasicSymbolRef::SF_Indirect)) { 315 auto *Fallback = dyn_cast<GlobalValue>( 316 cast<GlobalAlias>(GV)->getAliasee()->stripPointerCasts()); 317 if (!Fallback) 318 return make_error<StringError>("Invalid weak external", 319 inconvertibleErrorCode()); 320 std::string FallbackName; 321 raw_string_ostream OS(FallbackName); 322 Msymtab.printSymbolName(OS, Fallback); 323 OS.flush(); 324 setStr(Uncommon().COFFWeakExternFallbackName, Saver.save(FallbackName)); 325 } 326 } 327 328 if (!GO->getSection().empty()) 329 setStr(Uncommon().SectionName, Saver.save(GO->getSection())); 330 331 return Error::success(); 332 } 333 334 Error Builder::build(ArrayRef<Module *> IRMods) { 335 storage::Header Hdr; 336 337 assert(!IRMods.empty()); 338 Hdr.Version = storage::Header::kCurrentVersion; 339 setStr(Hdr.Producer, kExpectedProducerName); 340 setStr(Hdr.TargetTriple, IRMods[0]->getTargetTriple()); 341 setStr(Hdr.SourceFileName, IRMods[0]->getSourceFileName()); 342 TT = Triple(IRMods[0]->getTargetTriple()); 343 344 for (auto *M : IRMods) 345 if (Error Err = addModule(M)) 346 return Err; 347 348 COFFLinkerOptsOS.flush(); 349 setStr(Hdr.COFFLinkerOpts, Saver.save(COFFLinkerOpts)); 350 351 // We are about to fill in the header's range fields, so reserve space for it 352 // and copy it in afterwards. 353 Symtab.resize(sizeof(storage::Header)); 354 writeRange(Hdr.Modules, Mods); 355 writeRange(Hdr.Comdats, Comdats); 356 writeRange(Hdr.Symbols, Syms); 357 writeRange(Hdr.Uncommons, Uncommons); 358 writeRange(Hdr.DependentLibraries, DependentLibraries); 359 *reinterpret_cast<storage::Header *>(Symtab.data()) = Hdr; 360 return Error::success(); 361 } 362 363 } // end anonymous namespace 364 365 Error irsymtab::build(ArrayRef<Module *> Mods, SmallVector<char, 0> &Symtab, 366 StringTableBuilder &StrtabBuilder, 367 BumpPtrAllocator &Alloc) { 368 return Builder(Symtab, StrtabBuilder, Alloc).build(Mods); 369 } 370 371 // Upgrade a vector of bitcode modules created by an old version of LLVM by 372 // creating an irsymtab for them in the current format. 373 static Expected<FileContents> upgrade(ArrayRef<BitcodeModule> BMs) { 374 FileContents FC; 375 376 LLVMContext Ctx; 377 std::vector<Module *> Mods; 378 std::vector<std::unique_ptr<Module>> OwnedMods; 379 for (auto BM : BMs) { 380 Expected<std::unique_ptr<Module>> MOrErr = 381 BM.getLazyModule(Ctx, /*ShouldLazyLoadMetadata*/ true, 382 /*IsImporting*/ false); 383 if (!MOrErr) 384 return MOrErr.takeError(); 385 386 Mods.push_back(MOrErr->get()); 387 OwnedMods.push_back(std::move(*MOrErr)); 388 } 389 390 StringTableBuilder StrtabBuilder(StringTableBuilder::RAW); 391 BumpPtrAllocator Alloc; 392 if (Error E = build(Mods, FC.Symtab, StrtabBuilder, Alloc)) 393 return std::move(E); 394 395 StrtabBuilder.finalizeInOrder(); 396 FC.Strtab.resize(StrtabBuilder.getSize()); 397 StrtabBuilder.write((uint8_t *)FC.Strtab.data()); 398 399 FC.TheReader = {{FC.Symtab.data(), FC.Symtab.size()}, 400 {FC.Strtab.data(), FC.Strtab.size()}}; 401 return std::move(FC); 402 } 403 404 Expected<FileContents> irsymtab::readBitcode(const BitcodeFileContents &BFC) { 405 if (BFC.Mods.empty()) 406 return make_error<StringError>("Bitcode file does not contain any modules", 407 inconvertibleErrorCode()); 408 409 if (!DisableBitcodeVersionUpgrade) { 410 if (BFC.StrtabForSymtab.empty() || 411 BFC.Symtab.size() < sizeof(storage::Header)) 412 return upgrade(BFC.Mods); 413 414 // We cannot use the regular reader to read the version and producer, 415 // because it will expect the header to be in the current format. The only 416 // thing we can rely on is that the version and producer will be present as 417 // the first struct elements. 418 auto *Hdr = reinterpret_cast<const storage::Header *>(BFC.Symtab.data()); 419 unsigned Version = Hdr->Version; 420 StringRef Producer = Hdr->Producer.get(BFC.StrtabForSymtab); 421 if (Version != storage::Header::kCurrentVersion || 422 Producer != kExpectedProducerName) 423 return upgrade(BFC.Mods); 424 } 425 426 FileContents FC; 427 FC.TheReader = {{BFC.Symtab.data(), BFC.Symtab.size()}, 428 {BFC.StrtabForSymtab.data(), BFC.StrtabForSymtab.size()}}; 429 430 // Finally, make sure that the number of modules in the symbol table matches 431 // the number of modules in the bitcode file. If they differ, it may mean that 432 // the bitcode file was created by binary concatenation, so we need to create 433 // a new symbol table from scratch. 434 if (FC.TheReader.getNumModules() != BFC.Mods.size()) 435 return upgrade(std::move(BFC.Mods)); 436 437 return std::move(FC); 438 } 439