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/MC/StringTableBuilder.h"
  26 #include "llvm/Object/ModuleSymbolTable.h"
  27 #include "llvm/Object/SymbolicFile.h"
  28 #include "llvm/Support/Allocator.h"
  29 #include "llvm/Support/Casting.h"
  30 #include "llvm/Support/CommandLine.h"
  31 #include "llvm/Support/Error.h"
  32 #include "llvm/Support/StringSaver.h"
  33 #include "llvm/Support/VCSRevision.h"
  34 #include "llvm/Support/raw_ostream.h"
  35 #include "llvm/TargetParser/Triple.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 cl::opt<bool> DisableBitcodeVersionUpgrade(
  45     "disable-bitcode-version-upgrade", 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 static DenseSet<StringRef> buildPreservedSymbolsSet() {
 219   return DenseSet<StringRef>(std::begin(PreservedSymbols),
 220                              std::end(PreservedSymbols));
 221 }
 222
 223 Error Builder::addSymbol(const ModuleSymbolTable &Msymtab,
 224                          const SmallPtrSet<GlobalValue *, 4> &Used,
 225                          ModuleSymbolTable::Symbol Msym) {
 226   Syms.emplace_back();
 227   storage::Symbol &Sym = Syms.back();
 228   Sym = {};
 229
 230   storage::Uncommon *Unc = nullptr;
 231   auto Uncommon = [&]() -> storage::Uncommon & {
 232     if (Unc)
 233       return *Unc;
 234     Sym.Flags |= 1 << storage::Symbol::FB_has_uncommon;
 235     Uncommons.emplace_back();
 236     Unc = &Uncommons.back();
 237     *Unc = {};
 238     setStr(Unc->COFFWeakExternFallbackName, "");
 239     setStr(Unc->SectionName, "");
 240     return *Unc;
 241   };
 242
 243   SmallString<64> Name;
 244   {
 245     raw_svector_ostream OS(Name);
 246     Msymtab.printSymbolName(OS, Msym);
 247   }
 248   setStr(Sym.Name, Saver.save(Name.str()));
 249
 250   auto Flags = Msymtab.getSymbolFlags(Msym);
 251   if (Flags & object::BasicSymbolRef::SF_Undefined)
 252     Sym.Flags |= 1 << storage::Symbol::FB_undefined;
 253   if (Flags & object::BasicSymbolRef::SF_Weak)
 254     Sym.Flags |= 1 << storage::Symbol::FB_weak;
 255   if (Flags & object::BasicSymbolRef::SF_Common)
 256     Sym.Flags |= 1 << storage::Symbol::FB_common;
 257   if (Flags & object::BasicSymbolRef::SF_Indirect)
 258     Sym.Flags |= 1 << storage::Symbol::FB_indirect;
 259   if (Flags & object::BasicSymbolRef::SF_Global)
 260     Sym.Flags |= 1 << storage::Symbol::FB_global;
 261   if (Flags & object::BasicSymbolRef::SF_FormatSpecific)
 262     Sym.Flags |= 1 << storage::Symbol::FB_format_specific;
 263   if (Flags & object::BasicSymbolRef::SF_Executable)
 264     Sym.Flags |= 1 << storage::Symbol::FB_executable;
 265
 266   Sym.ComdatIndex = -1;
 267   auto *GV = dyn_cast_if_present<GlobalValue *>(Msym);
 268   if (!GV) {
 269     // Undefined module asm symbols act as GC roots and are implicitly used.
 270     if (Flags & object::BasicSymbolRef::SF_Undefined)
 271       Sym.Flags |= 1 << storage::Symbol::FB_used;
 272     setStr(Sym.IRName, "");
 273     return Error::success();
 274   }
 275
 276   setStr(Sym.IRName, GV->getName());
 277
 278   static const DenseSet<StringRef> PreservedSymbolsSet =
 279       buildPreservedSymbolsSet();
 280   bool IsPreservedSymbol = PreservedSymbolsSet.contains(GV->getName());
 281
 282   if (Used.count(GV) || IsPreservedSymbol)
 283     Sym.Flags |= 1 << storage::Symbol::FB_used;
 284   if (GV->isThreadLocal())
 285     Sym.Flags |= 1 << storage::Symbol::FB_tls;
 286   if (GV->hasGlobalUnnamedAddr())
 287     Sym.Flags |= 1 << storage::Symbol::FB_unnamed_addr;
 288   if (GV->canBeOmittedFromSymbolTable())
 289     Sym.Flags |= 1 << storage::Symbol::FB_may_omit;
 290   Sym.Flags |= unsigned(GV->getVisibility()) << storage::Symbol::FB_visibility;
 291
 292   if (Flags & object::BasicSymbolRef::SF_Common) {
 293     auto *GVar = dyn_cast<GlobalVariable>(GV);
 294     if (!GVar)
 295       return make_error<StringError>("Only variables can have common linkage!",
 296                                      inconvertibleErrorCode());
 297     Uncommon().CommonSize =
 298         GV->getParent()->getDataLayout().getTypeAllocSize(GV->getValueType());
 299     Uncommon().CommonAlign = GVar->getAlign() ? GVar->getAlign()->value() : 0;
 300   }
 301
 302   const GlobalObject *GO = GV->getAliaseeObject();
 303   if (!GO) {
 304     if (isa<GlobalIFunc>(GV))
 305       GO = cast<GlobalIFunc>(GV)->getResolverFunction();
 306     if (!GO)
 307       return make_error<StringError>("Unable to determine comdat of alias!",
 308                                      inconvertibleErrorCode());
 309   }
 310   if (const Comdat *C = GO->getComdat()) {
 311     Expected<int> ComdatIndexOrErr = getComdatIndex(C, GV->getParent());
 312     if (!ComdatIndexOrErr)
 313       return ComdatIndexOrErr.takeError();
 314     Sym.ComdatIndex = *ComdatIndexOrErr;
 315   }
 316
 317   if (TT.isOSBinFormatCOFF()) {
 318     emitLinkerFlagsForGlobalCOFF(COFFLinkerOptsOS, GV, TT, Mang);
 319
 320     if ((Flags & object::BasicSymbolRef::SF_Weak) &&
 321         (Flags & object::BasicSymbolRef::SF_Indirect)) {
 322       auto *Fallback = dyn_cast<GlobalValue>(
 323           cast<GlobalAlias>(GV)->getAliasee()->stripPointerCasts());
 324       if (!Fallback)
 325         return make_error<StringError>("Invalid weak external",
 326                                        inconvertibleErrorCode());
 327       std::string FallbackName;
 328       raw_string_ostream OS(FallbackName);
 329       Msymtab.printSymbolName(OS, Fallback);
 330       OS.flush();
 331       setStr(Uncommon().COFFWeakExternFallbackName, Saver.save(FallbackName));
 332     }
 333   }
 334
 335   if (!GO->getSection().empty())
 336     setStr(Uncommon().SectionName, Saver.save(GO->getSection()));
 337
 338   return Error::success();
 339 }
 340
 341 Error Builder::build(ArrayRef<Module *> IRMods) {
 342   storage::Header Hdr;
 343
 344   assert(!IRMods.empty());
 345   Hdr.Version = storage::Header::kCurrentVersion;
 346   setStr(Hdr.Producer, kExpectedProducerName);
 347   setStr(Hdr.TargetTriple, IRMods[0]->getTargetTriple());
 348   setStr(Hdr.SourceFileName, IRMods[0]->getSourceFileName());
 349   TT = Triple(IRMods[0]->getTargetTriple());
 350
 351   for (auto *M : IRMods)
 352     if (Error Err = addModule(M))
 353       return Err;
 354
 355   COFFLinkerOptsOS.flush();
 356   setStr(Hdr.COFFLinkerOpts, Saver.save(COFFLinkerOpts));
 357
 358   // We are about to fill in the header's range fields, so reserve space for it
 359   // and copy it in afterwards.
 360   Symtab.resize(sizeof(storage::Header));
 361   writeRange(Hdr.Modules, Mods);
 362   writeRange(Hdr.Comdats, Comdats);
 363   writeRange(Hdr.Symbols, Syms);
 364   writeRange(Hdr.Uncommons, Uncommons);
 365   writeRange(Hdr.DependentLibraries, DependentLibraries);
 366   *reinterpret_cast<storage::Header *>(Symtab.data()) = Hdr;
 367   return Error::success();
 368 }
 369
 370 } // end anonymous namespace
 371
 372 Error irsymtab::build(ArrayRef<Module *> Mods, SmallVector<char, 0> &Symtab,
 373                       StringTableBuilder &StrtabBuilder,
 374                       BumpPtrAllocator &Alloc) {
 375   return Builder(Symtab, StrtabBuilder, Alloc).build(Mods);
 376 }
 377
 378 // Upgrade a vector of bitcode modules created by an old version of LLVM by
 379 // creating an irsymtab for them in the current format.
 380 static Expected<FileContents> upgrade(ArrayRef<BitcodeModule> BMs) {
 381   FileContents FC;
 382
 383   LLVMContext Ctx;
 384   std::vector<Module *> Mods;
 385   std::vector<std::unique_ptr<Module>> OwnedMods;
 386   for (auto BM : BMs) {
 387     Expected<std::unique_ptr<Module>> MOrErr =
 388         BM.getLazyModule(Ctx, /*ShouldLazyLoadMetadata*/ true,
 389                          /*IsImporting*/ false);
 390     if (!MOrErr)
 391       return MOrErr.takeError();
 392
 393     Mods.push_back(MOrErr->get());
 394     OwnedMods.push_back(std::move(*MOrErr));
 395   }
 396
 397   StringTableBuilder StrtabBuilder(StringTableBuilder::RAW);
 398   BumpPtrAllocator Alloc;
 399   if (Error E = build(Mods, FC.Symtab, StrtabBuilder, Alloc))
 400     return std::move(E);
 401
 402   StrtabBuilder.finalizeInOrder();
 403   FC.Strtab.resize(StrtabBuilder.getSize());
 404   StrtabBuilder.write((uint8_t *)FC.Strtab.data());
 405
 406   FC.TheReader = {{FC.Symtab.data(), FC.Symtab.size()},
 407                   {FC.Strtab.data(), FC.Strtab.size()}};
 408   return std::move(FC);
 409 }
 410
 411 Expected<FileContents> irsymtab::readBitcode(const BitcodeFileContents &BFC) {
 412   if (BFC.Mods.empty())
 413     return make_error<StringError>("Bitcode file does not contain any modules",
 414                                    inconvertibleErrorCode());
 415
 416   if (!DisableBitcodeVersionUpgrade) {
 417     if (BFC.StrtabForSymtab.empty() ||
 418         BFC.Symtab.size() < sizeof(storage::Header))
 419       return upgrade(BFC.Mods);
 420
 421     // We cannot use the regular reader to read the version and producer,
 422     // because it will expect the header to be in the current format. The only
 423     // thing we can rely on is that the version and producer will be present as
 424     // the first struct elements.
 425     auto *Hdr = reinterpret_cast<const storage::Header *>(BFC.Symtab.data());
 426     unsigned Version = Hdr->Version;
 427     StringRef Producer = Hdr->Producer.get(BFC.StrtabForSymtab);
 428     if (Version != storage::Header::kCurrentVersion ||
 429         Producer != kExpectedProducerName)
 430       return upgrade(BFC.Mods);
 431   }
 432
 433   FileContents FC;
 434   FC.TheReader = {{BFC.Symtab.data(), BFC.Symtab.size()},
 435                   {BFC.StrtabForSymtab.data(), BFC.StrtabForSymtab.size()}};
 436
 437   // Finally, make sure that the number of modules in the symbol table matches
 438   // the number of modules in the bitcode file. If they differ, it may mean that
 439   // the bitcode file was created by binary concatenation, so we need to create
 440   // a new symbol table from scratch.
 441   if (FC.TheReader.getNumModules() != BFC.Mods.size())
 442     return upgrade(std::move(BFC.Mods));
 443
 444   return std::move(FC);
 445 }