llvm/lib/Object/IRSymtab.cpp

   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/Bitcode/BitcodeReader.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/IR/RuntimeLibcalls.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 "llvm/TargetParser/Triple.h"
  37 #include <cassert>
  38 #include <string>
  39 #include <utility>
  40 #include <vector>
  41
  42 using namespace llvm;
  43 using namespace irsymtab;
  44
  45 static cl::opt<bool> DisableBitcodeVersionUpgrade(
  46     "disable-bitcode-version-upgrade", cl::Hidden,
  47     cl::desc("Disable automatic bitcode upgrade for version mismatch"));
  48
  49 static const char *PreservedSymbols[] = {
  50     // There are global variables, so put it here instead of in
  51     // RuntimeLibcalls.def.
  52     // TODO: Are there similar such variables?
  53     "__ssp_canary_word",
  54     "__stack_chk_guard",
  55 };
  56
  57 namespace {
  58
  59 const char *getExpectedProducerName() {
  60   static char DefaultName[] = LLVM_VERSION_STRING
  61 #ifdef LLVM_REVISION
  62       " " LLVM_REVISION
  63 #endif
  64       ;
  65   // Allows for testing of the irsymtab writer and upgrade mechanism. This
  66   // environment variable should not be set by users.
  67   if (char *OverrideName = getenv("LLVM_OVERRIDE_PRODUCER"))
  68     return OverrideName;
  69   return DefaultName;
  70 }
  71
  72 const char *kExpectedProducerName = getExpectedProducerName();
  73
  74 /// Stores the temporary state that is required to build an IR symbol table.
  75 struct Builder {
  76   SmallVector<char, 0> &Symtab;
  77   StringTableBuilder &StrtabBuilder;
  78   StringSaver Saver;
  79
  80   // This ctor initializes a StringSaver using the passed in BumpPtrAllocator.
  81   // The StringTableBuilder does not create a copy of any strings added to it,
  82   // so this provides somewhere to store any strings that we create.
  83   Builder(SmallVector<char, 0> &Symtab, StringTableBuilder &StrtabBuilder,
  84           BumpPtrAllocator &Alloc)
  85       : Symtab(Symtab), StrtabBuilder(StrtabBuilder), Saver(Alloc) {}
  86
  87   DenseMap<const Comdat *, int> ComdatMap;
  88   Mangler Mang;
  89   Triple TT;
  90
  91   std::vector<storage::Comdat> Comdats;
  92   std::vector<storage::Module> Mods;
  93   std::vector<storage::Symbol> Syms;
  94   std::vector<storage::Uncommon> Uncommons;
  95
  96   std::string COFFLinkerOpts;
  97   raw_string_ostream COFFLinkerOptsOS{COFFLinkerOpts};
  98
  99   std::vector<storage::Str> DependentLibraries;
 100
 101   void setStr(storage::Str &S, StringRef Value) {
 102     S.Offset = StrtabBuilder.add(Value);
 103     S.Size = Value.size();
 104   }
 105
 106   template <typename T>
 107   void writeRange(storage::Range<T> &R, const std::vector<T> &Objs) {
 108     R.Offset = Symtab.size();
 109     R.Size = Objs.size();
 110     Symtab.insert(Symtab.end(), reinterpret_cast<const char *>(Objs.data()),
 111                   reinterpret_cast<const char *>(Objs.data() + Objs.size()));
 112   }
 113
 114   Expected<int> getComdatIndex(const Comdat *C, const Module *M);
 115
 116   Error addModule(Module *M);
 117   Error addSymbol(const ModuleSymbolTable &Msymtab,
 118                   const SmallPtrSet<GlobalValue *, 4> &Used,
 119                   ModuleSymbolTable::Symbol Sym);
 120
 121   Error build(ArrayRef<Module *> Mods);
 122 };
 123
 124 Error Builder::addModule(Module *M) {
 125   if (M->getDataLayoutStr().empty())
 126     return make_error<StringError>("input module has no datalayout",
 127                                    inconvertibleErrorCode());
 128
 129   // Symbols in the llvm.used list will get the FB_Used bit and will not be
 130   // internalized. We do this for llvm.compiler.used as well:
 131   //
 132   // IR symbol table tracks module-level asm symbol references but not inline
 133   // asm. A symbol only referenced by inline asm is not in the IR symbol table,
 134   // so we may not know that the definition (in another translation unit) is
 135   // referenced. That definition may have __attribute__((used)) (which lowers to
 136   // llvm.compiler.used on ELF targets) to communicate to the compiler that it
 137   // may be used by inline asm. The usage is perfectly fine, so we treat
 138   // llvm.compiler.used conservatively as llvm.used to work around our own
 139   // limitation.
 140   SmallVector<GlobalValue *, 4> UsedV;
 141   collectUsedGlobalVariables(*M, UsedV, /*CompilerUsed=*/false);
 142   collectUsedGlobalVariables(*M, UsedV, /*CompilerUsed=*/true);
 143   SmallPtrSet<GlobalValue *, 4> Used(UsedV.begin(), UsedV.end());
 144
 145   ModuleSymbolTable Msymtab;
 146   Msymtab.addModule(M);
 147
 148   storage::Module Mod;
 149   Mod.Begin = Syms.size();
 150   Mod.End = Syms.size() + Msymtab.symbols().size();
 151   Mod.UncBegin = Uncommons.size();
 152   Mods.push_back(Mod);
 153
 154   if (TT.isOSBinFormatCOFF()) {
 155     if (auto E = M->materializeMetadata())
 156       return E;
 157     if (NamedMDNode *LinkerOptions =
 158             M->getNamedMetadata("llvm.linker.options")) {
 159       for (MDNode *MDOptions : LinkerOptions->operands())
 160         for (const MDOperand &MDOption : cast<MDNode>(MDOptions)->operands())
 161           COFFLinkerOptsOS << " " << cast<MDString>(MDOption)->getString();
 162     }
 163   }
 164
 165   if (TT.isOSBinFormatELF()) {
 166     if (auto E = M->materializeMetadata())
 167       return E;
 168     if (NamedMDNode *N = M->getNamedMetadata("llvm.dependent-libraries")) {
 169       for (MDNode *MDOptions : N->operands()) {
 170         const auto OperandStr =
 171             cast<MDString>(cast<MDNode>(MDOptions)->getOperand(0))->getString();
 172         storage::Str Specifier;
 173         setStr(Specifier, OperandStr);
 174         DependentLibraries.emplace_back(Specifier);
 175       }
 176     }
 177   }
 178
 179   for (ModuleSymbolTable::Symbol Msym : Msymtab.symbols())
 180     if (Error Err = addSymbol(Msymtab, Used, Msym))
 181       return Err;
 182
 183   return Error::success();
 184 }
 185
 186 Expected<int> Builder::getComdatIndex(const Comdat *C, const Module *M) {
 187   auto P = ComdatMap.insert(std::make_pair(C, Comdats.size()));
 188   if (P.second) {
 189     std::string Name;
 190     if (TT.isOSBinFormatCOFF()) {
 191       const GlobalValue *GV = M->getNamedValue(C->getName());
 192       if (!GV)
 193         return make_error<StringError>("Could not find leader",
 194                                        inconvertibleErrorCode());
 195       // Internal leaders do not affect symbol resolution, therefore they do not
 196       // appear in the symbol table.
 197       if (GV->hasLocalLinkage()) {
 198         P.first->second = -1;
 199         return -1;
 200       }
 201       llvm::raw_string_ostream OS(Name);
 202       Mang.getNameWithPrefix(OS, GV, false);
 203     } else {
 204       Name = std::string(C->getName());
 205     }
 206
 207     storage::Comdat Comdat;
 208     setStr(Comdat.Name, Saver.save(Name));
 209     Comdat.SelectionKind = C->getSelectionKind();
 210     Comdats.push_back(Comdat);
 211   }
 212
 213   return P.first->second;
 214 }
 215
 216 static DenseSet<StringRef> buildPreservedSymbolsSet(const Triple &TT) {
 217   DenseSet<StringRef> PreservedSymbolSet(std::begin(PreservedSymbols),
 218                                          std::end(PreservedSymbols));
 219
 220   RTLIB::RuntimeLibcallsInfo Libcalls(TT);
 221   for (const char *Name : Libcalls.getLibcallNames()) {
 222     if (Name)
 223       PreservedSymbolSet.insert(Name);
 224   }
 225   return PreservedSymbolSet;
 226 }
 227
 228 Error Builder::addSymbol(const ModuleSymbolTable &Msymtab,
 229                          const SmallPtrSet<GlobalValue *, 4> &Used,
 230                          ModuleSymbolTable::Symbol Msym) {
 231   Syms.emplace_back();
 232   storage::Symbol &Sym = Syms.back();
 233   Sym = {};
 234
 235   storage::Uncommon *Unc = nullptr;
 236   auto Uncommon = [&]() -> storage::Uncommon & {
 237     if (Unc)
 238       return *Unc;
 239     Sym.Flags |= 1 << storage::Symbol::FB_has_uncommon;
 240     Uncommons.emplace_back();
 241     Unc = &Uncommons.back();
 242     *Unc = {};
 243     setStr(Unc->COFFWeakExternFallbackName, "");
 244     setStr(Unc->SectionName, "");
 245     return *Unc;
 246   };
 247
 248   SmallString<64> Name;
 249   {
 250     raw_svector_ostream OS(Name);
 251     Msymtab.printSymbolName(OS, Msym);
 252   }
 253   setStr(Sym.Name, Saver.save(Name.str()));
 254
 255   auto Flags = Msymtab.getSymbolFlags(Msym);
 256   if (Flags & object::BasicSymbolRef::SF_Undefined)
 257     Sym.Flags |= 1 << storage::Symbol::FB_undefined;
 258   if (Flags & object::BasicSymbolRef::SF_Weak)
 259     Sym.Flags |= 1 << storage::Symbol::FB_weak;
 260   if (Flags & object::BasicSymbolRef::SF_Common)
 261     Sym.Flags |= 1 << storage::Symbol::FB_common;
 262   if (Flags & object::BasicSymbolRef::SF_Indirect)
 263     Sym.Flags |= 1 << storage::Symbol::FB_indirect;
 264   if (Flags & object::BasicSymbolRef::SF_Global)
 265     Sym.Flags |= 1 << storage::Symbol::FB_global;
 266   if (Flags & object::BasicSymbolRef::SF_FormatSpecific)
 267     Sym.Flags |= 1 << storage::Symbol::FB_format_specific;
 268   if (Flags & object::BasicSymbolRef::SF_Executable)
 269     Sym.Flags |= 1 << storage::Symbol::FB_executable;
 270
 271   Sym.ComdatIndex = -1;
 272   auto *GV = dyn_cast_if_present<GlobalValue *>(Msym);
 273   if (!GV) {
 274     // Undefined module asm symbols act as GC roots and are implicitly used.
 275     if (Flags & object::BasicSymbolRef::SF_Undefined)
 276       Sym.Flags |= 1 << storage::Symbol::FB_used;
 277     setStr(Sym.IRName, "");
 278     return Error::success();
 279   }
 280
 281   setStr(Sym.IRName, GV->getName());
 282
 283   static const DenseSet<StringRef> PreservedSymbolsSet =
 284       buildPreservedSymbolsSet(
 285           llvm::Triple(GV->getParent()->getTargetTriple()));
 286   bool IsPreservedSymbol = PreservedSymbolsSet.contains(GV->getName());
 287
 288   if (Used.count(GV) || IsPreservedSymbol)
 289     Sym.Flags |= 1 << storage::Symbol::FB_used;
 290   if (GV->isThreadLocal())
 291     Sym.Flags |= 1 << storage::Symbol::FB_tls;
 292   if (GV->hasGlobalUnnamedAddr())
 293     Sym.Flags |= 1 << storage::Symbol::FB_unnamed_addr;
 294   if (GV->canBeOmittedFromSymbolTable())
 295     Sym.Flags |= 1 << storage::Symbol::FB_may_omit;
 296   Sym.Flags |= unsigned(GV->getVisibility()) << storage::Symbol::FB_visibility;
 297
 298   if (Flags & object::BasicSymbolRef::SF_Common) {
 299     auto *GVar = dyn_cast<GlobalVariable>(GV);
 300     if (!GVar)
 301       return make_error<StringError>("Only variables can have common linkage!",
 302                                      inconvertibleErrorCode());
 303     Uncommon().CommonSize =
 304         GV->getDataLayout().getTypeAllocSize(GV->getValueType());
 305     Uncommon().CommonAlign = GVar->getAlign() ? GVar->getAlign()->value() : 0;
 306   }
 307
 308   const GlobalObject *GO = GV->getAliaseeObject();
 309   if (!GO) {
 310     if (isa<GlobalIFunc>(GV))
 311       GO = cast<GlobalIFunc>(GV)->getResolverFunction();
 312     if (!GO)
 313       return make_error<StringError>("Unable to determine comdat of alias!",
 314                                      inconvertibleErrorCode());
 315   }
 316   if (const Comdat *C = GO->getComdat()) {
 317     Expected<int> ComdatIndexOrErr = getComdatIndex(C, GV->getParent());
 318     if (!ComdatIndexOrErr)
 319       return ComdatIndexOrErr.takeError();
 320     Sym.ComdatIndex = *ComdatIndexOrErr;
 321   }
 322
 323   if (TT.isOSBinFormatCOFF()) {
 324     emitLinkerFlagsForGlobalCOFF(COFFLinkerOptsOS, GV, TT, Mang);
 325
 326     if ((Flags & object::BasicSymbolRef::SF_Weak) &&
 327         (Flags & object::BasicSymbolRef::SF_Indirect)) {
 328       auto *Fallback = dyn_cast<GlobalValue>(
 329           cast<GlobalAlias>(GV)->getAliasee()->stripPointerCasts());
 330       if (!Fallback)
 331         return make_error<StringError>("Invalid weak external",
 332                                        inconvertibleErrorCode());
 333       std::string FallbackName;
 334       raw_string_ostream OS(FallbackName);
 335       Msymtab.printSymbolName(OS, Fallback);
 336       OS.flush();
 337       setStr(Uncommon().COFFWeakExternFallbackName, Saver.save(FallbackName));
 338     }
 339   }
 340
 341   if (!GO->getSection().empty())
 342     setStr(Uncommon().SectionName, Saver.save(GO->getSection()));
 343
 344   return Error::success();
 345 }
 346
 347 Error Builder::build(ArrayRef<Module *> IRMods) {
 348   storage::Header Hdr;
 349
 350   assert(!IRMods.empty());
 351   Hdr.Version = storage::Header::kCurrentVersion;
 352   setStr(Hdr.Producer, kExpectedProducerName);
 353   setStr(Hdr.TargetTriple, IRMods[0]->getTargetTriple());
 354   setStr(Hdr.SourceFileName, IRMods[0]->getSourceFileName());
 355   TT = Triple(IRMods[0]->getTargetTriple());
 356
 357   for (auto *M : IRMods)
 358     if (Error Err = addModule(M))
 359       return Err;
 360
 361   COFFLinkerOptsOS.flush();
 362   setStr(Hdr.COFFLinkerOpts, Saver.save(COFFLinkerOpts));
 363
 364   // We are about to fill in the header's range fields, so reserve space for it
 365   // and copy it in afterwards.
 366   Symtab.resize(sizeof(storage::Header));
 367   writeRange(Hdr.Modules, Mods);
 368   writeRange(Hdr.Comdats, Comdats);
 369   writeRange(Hdr.Symbols, Syms);
 370   writeRange(Hdr.Uncommons, Uncommons);
 371   writeRange(Hdr.DependentLibraries, DependentLibraries);
 372   *reinterpret_cast<storage::Header *>(Symtab.data()) = Hdr;
 373   return Error::success();
 374 }
 375
 376 } // end anonymous namespace
 377
 378 Error irsymtab::build(ArrayRef<Module *> Mods, SmallVector<char, 0> &Symtab,
 379                       StringTableBuilder &StrtabBuilder,
 380                       BumpPtrAllocator &Alloc) {
 381   return Builder(Symtab, StrtabBuilder, Alloc).build(Mods);
 382 }
 383
 384 // Upgrade a vector of bitcode modules created by an old version of LLVM by
 385 // creating an irsymtab for them in the current format.
 386 static Expected<FileContents> upgrade(ArrayRef<BitcodeModule> BMs) {
 387   FileContents FC;
 388
 389   LLVMContext Ctx;
 390   std::vector<Module *> Mods;
 391   std::vector<std::unique_ptr<Module>> OwnedMods;
 392   for (auto BM : BMs) {
 393     Expected<std::unique_ptr<Module>> MOrErr =
 394         BM.getLazyModule(Ctx, /*ShouldLazyLoadMetadata*/ true,
 395                          /*IsImporting*/ false);
 396     if (!MOrErr)
 397       return MOrErr.takeError();
 398
 399     Mods.push_back(MOrErr->get());
 400     OwnedMods.push_back(std::move(*MOrErr));
 401   }
 402
 403   StringTableBuilder StrtabBuilder(StringTableBuilder::RAW);
 404   BumpPtrAllocator Alloc;
 405   if (Error E = build(Mods, FC.Symtab, StrtabBuilder, Alloc))
 406     return std::move(E);
 407
 408   StrtabBuilder.finalizeInOrder();
 409   FC.Strtab.resize(StrtabBuilder.getSize());
 410   StrtabBuilder.write((uint8_t *)FC.Strtab.data());
 411
 412   FC.TheReader = {{FC.Symtab.data(), FC.Symtab.size()},
 413                   {FC.Strtab.data(), FC.Strtab.size()}};
 414   return std::move(FC);
 415 }
 416
 417 Expected<FileContents> irsymtab::readBitcode(const BitcodeFileContents &BFC) {
 418   if (BFC.Mods.empty())
 419     return make_error<StringError>("Bitcode file does not contain any modules",
 420                                    inconvertibleErrorCode());
 421
 422   if (!DisableBitcodeVersionUpgrade) {
 423     if (BFC.StrtabForSymtab.empty() ||
 424         BFC.Symtab.size() < sizeof(storage::Header))
 425       return upgrade(BFC.Mods);
 426
 427     // We cannot use the regular reader to read the version and producer,
 428     // because it will expect the header to be in the current format. The only
 429     // thing we can rely on is that the version and producer will be present as
 430     // the first struct elements.
 431     auto *Hdr = reinterpret_cast<const storage::Header *>(BFC.Symtab.data());
 432     unsigned Version = Hdr->Version;
 433     StringRef Producer = Hdr->Producer.get(BFC.StrtabForSymtab);
 434     if (Version != storage::Header::kCurrentVersion ||
 435         Producer != kExpectedProducerName)
 436       return upgrade(BFC.Mods);
 437   }
 438
 439   FileContents FC;
 440   FC.TheReader = {{BFC.Symtab.data(), BFC.Symtab.size()},
 441                   {BFC.StrtabForSymtab.data(), BFC.StrtabForSymtab.size()}};
 442
 443   // Finally, make sure that the number of modules in the symbol table matches
 444   // the number of modules in the bitcode file. If they differ, it may mean that
 445   // the bitcode file was created by binary concatenation, so we need to create
 446   // a new symbol table from scratch.
 447   if (FC.TheReader.getNumModules() != BFC.Mods.size())
 448     return upgrade(std::move(BFC.Mods));
 449
 450   return std::move(FC);
 451 }