//===- IRSymtab.cpp - implementation of IR symbol tables ------------------===//

//

// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

// See https://llvm.org/LICENSE.txt for license information.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

//

//===----------------------------------------------------------------------===//

#include "llvm/Object/IRSymtab.h"

#include "llvm/ADT/ArrayRef.h"

#include "llvm/ADT/DenseMap.h"

#include "llvm/ADT/SmallPtrSet.h"

#include "llvm/ADT/SmallString.h"

#include "llvm/ADT/SmallVector.h"

#include "llvm/ADT/StringRef.h"

#include "llvm/Bitcode/BitcodeReader.h"

#include "llvm/Config/llvm-config.h"

#include "llvm/IR/Comdat.h"

#include "llvm/IR/DataLayout.h"

#include "llvm/IR/GlobalAlias.h"

#include "llvm/IR/GlobalObject.h"

#include "llvm/IR/Mangler.h"

#include "llvm/IR/Metadata.h"

#include "llvm/IR/Module.h"

#include "llvm/MC/StringTableBuilder.h"

#include "llvm/Object/ModuleSymbolTable.h"

#include "llvm/Object/SymbolicFile.h"

#include "llvm/Support/Allocator.h"

#include "llvm/Support/Casting.h"

#include "llvm/Support/CommandLine.h"

#include "llvm/Support/Error.h"

#include "llvm/Support/StringSaver.h"

#include "llvm/Support/VCSRevision.h"

#include "llvm/Support/raw_ostream.h"

#include "llvm/TargetParser/Triple.h"

#include <cassert>

#include <string>

#include <utility>

#include <vector>

using namespace llvm;

using namespace irsymtab;

static cl::opt<bool> DisableBitcodeVersionUpgrade(

    "disable-bitcode-version-upgrade", cl::Hidden,

    cl::desc("Disable automatic bitcode upgrade for version mismatch"));

static const char *PreservedSymbols[] = {

#define HANDLE_LIBCALL(code, name) name,

#include "llvm/IR/RuntimeLibcalls.def"

#undef HANDLE_LIBCALL

    // There are global variables, so put it here instead of in

    // RuntimeLibcalls.def.

    // TODO: Are there similar such variables?

    "__ssp_canary_word",

    "__stack_chk_guard",

};

namespace {

const char *getExpectedProducerName() {

  static char DefaultName[] = LLVM_VERSION_STRING

#ifdef LLVM_REVISION

      " " LLVM_REVISION

#endif

      ;

  // Allows for testing of the irsymtab writer and upgrade mechanism. This

  // environment variable should not be set by users.

  if (char *OverrideName = getenv("LLVM_OVERRIDE_PRODUCER"))

    return OverrideName;

  return DefaultName;

}

const char *kExpectedProducerName = getExpectedProducerName();

/// Stores the temporary state that is required to build an IR symbol table.

struct Builder {

  SmallVector<char, 0> &Symtab;

  StringTableBuilder &StrtabBuilder;

  StringSaver Saver;

  // This ctor initializes a StringSaver using the passed in BumpPtrAllocator.

  // The StringTableBuilder does not create a copy of any strings added to it,

  // so this provides somewhere to store any strings that we create.

  Builder(SmallVector<char, 0> &Symtab, StringTableBuilder &StrtabBuilder,

          BumpPtrAllocator &Alloc)

      : Symtab(Symtab), StrtabBuilder(StrtabBuilder), Saver(Alloc) {}

  DenseMap<const Comdat *, int> ComdatMap;

  Mangler Mang;

  Triple TT;

  std::vector<storage::Comdat> Comdats;

  std::vector<storage::Module> Mods;

  std::vector<storage::Symbol> Syms;

  std::vector<storage::Uncommon> Uncommons;

  std::string COFFLinkerOpts;

  raw_string_ostream COFFLinkerOptsOS{COFFLinkerOpts};

  std::vector<storage::Str> DependentLibraries;

  void setStr(storage::Str &S, StringRef Value) {

    S.Offset = StrtabBuilder.add(Value);

    S.Size = Value.size();

  }

  template <typename T>

  void writeRange(storage::Range<T> &R, const std::vector<T> &Objs) {

    R.Offset = Symtab.size();

    R.Size = Objs.size();

    Symtab.insert(Symtab.end(), reinterpret_cast<const char *>(Objs.data()),

                  reinterpret_cast<const char *>(Objs.data() + Objs.size()));

  }

Unexecuted instantiation: IRSymtab.cpp:void (anonymous namespace)::Builder::writeRange<llvm::irsymtab::storage::Module>(llvm::irsymtab::storage::Range<llvm::irsymtab::storage::Module>&, std::__1::vector<llvm::irsymtab::storage::Module, std::__1::allocator<llvm::irsymtab::storage::Module> > const&)

Unexecuted instantiation: IRSymtab.cpp:void (anonymous namespace)::Builder::writeRange<llvm::irsymtab::storage::Comdat>(llvm::irsymtab::storage::Range<llvm::irsymtab::storage::Comdat>&, std::__1::vector<llvm::irsymtab::storage::Comdat, std::__1::allocator<llvm::irsymtab::storage::Comdat> > const&)

Unexecuted instantiation: IRSymtab.cpp:void (anonymous namespace)::Builder::writeRange<llvm::irsymtab::storage::Symbol>(llvm::irsymtab::storage::Range<llvm::irsymtab::storage::Symbol>&, std::__1::vector<llvm::irsymtab::storage::Symbol, std::__1::allocator<llvm::irsymtab::storage::Symbol> > const&)

Unexecuted instantiation: IRSymtab.cpp:void (anonymous namespace)::Builder::writeRange<llvm::irsymtab::storage::Uncommon>(llvm::irsymtab::storage::Range<llvm::irsymtab::storage::Uncommon>&, std::__1::vector<llvm::irsymtab::storage::Uncommon, std::__1::allocator<llvm::irsymtab::storage::Uncommon> > const&)

Unexecuted instantiation: IRSymtab.cpp:void (anonymous namespace)::Builder::writeRange<llvm::irsymtab::storage::Str>(llvm::irsymtab::storage::Range<llvm::irsymtab::storage::Str>&, std::__1::vector<llvm::irsymtab::storage::Str, std::__1::allocator<llvm::irsymtab::storage::Str> > const&)

  Expected<int> getComdatIndex(const Comdat *C, const Module *M);

  Error addModule(Module *M);

  Error addSymbol(const ModuleSymbolTable &Msymtab,

                  const SmallPtrSet<GlobalValue *, 4> &Used,

                  ModuleSymbolTable::Symbol Sym);

  Error build(ArrayRef<Module *> Mods);

};

Error Builder::addModule(Module *M) {

  if (M->getDataLayoutStr().empty())

    return make_error<StringError>("input module has no datalayout",

                                   inconvertibleErrorCode());

  // Symbols in the llvm.used list will get the FB_Used bit and will not be

  // internalized. We do this for llvm.compiler.used as well:

  //

  // IR symbol table tracks module-level asm symbol references but not inline

  // asm. A symbol only referenced by inline asm is not in the IR symbol table,

  // so we may not know that the definition (in another translation unit) is

  // referenced. That definition may have __attribute__((used)) (which lowers to

  // llvm.compiler.used on ELF targets) to communicate to the compiler that it

  // may be used by inline asm. The usage is perfectly fine, so we treat

  // llvm.compiler.used conservatively as llvm.used to work around our own

  // limitation.

  SmallVector<GlobalValue *, 4> UsedV;

  collectUsedGlobalVariables(*M, UsedV, /*CompilerUsed=*/false);

  collectUsedGlobalVariables(*M, UsedV, /*CompilerUsed=*/true);

  SmallPtrSet<GlobalValue *, 4> Used(UsedV.begin(), UsedV.end());

  ModuleSymbolTable Msymtab;

  Msymtab.addModule(M);

  storage::Module Mod;

  Mod.Begin = Syms.size();

  Mod.End = Syms.size() + Msymtab.symbols().size();

  Mod.UncBegin = Uncommons.size();

  Mods.push_back(Mod);

  if (TT.isOSBinFormatCOFF()) {

    if (auto E = M->materializeMetadata())

      return E;

    if (NamedMDNode *LinkerOptions =

            M->getNamedMetadata("llvm.linker.options")) {

      for (MDNode *MDOptions : LinkerOptions->operands())

        for (const MDOperand &MDOption : cast<MDNode>(MDOptions)->operands())

          COFFLinkerOptsOS << " " << cast<MDString>(MDOption)->getString();

    }

  }

  if (TT.isOSBinFormatELF()) {

    if (auto E = M->materializeMetadata())

      return E;

    if (NamedMDNode *N = M->getNamedMetadata("llvm.dependent-libraries")) {

      for (MDNode *MDOptions : N->operands()) {

        const auto OperandStr =

            cast<MDString>(cast<MDNode>(MDOptions)->getOperand(0))->getString();

        storage::Str Specifier;

        setStr(Specifier, OperandStr);

        DependentLibraries.emplace_back(Specifier);

      }

    }

  }

  for (ModuleSymbolTable::Symbol Msym : Msymtab.symbols())

    if (Error Err = addSymbol(Msymtab, Used, Msym))

      return Err;

  return Error::success();

}

Expected<int> Builder::getComdatIndex(const Comdat *C, const Module *M) {

  auto P = ComdatMap.insert(std::make_pair(C, Comdats.size()));

  if (P.second) {

    std::string Name;

    if (TT.isOSBinFormatCOFF()) {

      const GlobalValue *GV = M->getNamedValue(C->getName());

      if (!GV)

        return make_error<StringError>("Could not find leader",

                                       inconvertibleErrorCode());

      // Internal leaders do not affect symbol resolution, therefore they do not

      // appear in the symbol table.

      if (GV->hasLocalLinkage()) {

        P.first->second = -1;

        return -1;

      }

      llvm::raw_string_ostream OS(Name);

      Mang.getNameWithPrefix(OS, GV, false);

    } else {

      Name = std::string(C->getName());

    }

    storage::Comdat Comdat;

    setStr(Comdat.Name, Saver.save(Name));

    Comdat.SelectionKind = C->getSelectionKind();

    Comdats.push_back(Comdat);

  }

  return P.first->second;

}

static DenseSet<StringRef> buildPreservedSymbolsSet() {

  return DenseSet<StringRef>(std::begin(PreservedSymbols),

                             std::end(PreservedSymbols));

}

Error Builder::addSymbol(const ModuleSymbolTable &Msymtab,

                         const SmallPtrSet<GlobalValue *, 4> &Used,

                         ModuleSymbolTable::Symbol Msym) {

  Syms.emplace_back();

  storage::Symbol &Sym = Syms.back();

  Sym = {};

  storage::Uncommon *Unc = nullptr;

  auto Uncommon = [&]() -> storage::Uncommon & {

    if (Unc)

      return *Unc;

    Sym.Flags |= 1 << storage::Symbol::FB_has_uncommon;

    Uncommons.emplace_back();

    Unc = &Uncommons.back();

    *Unc = {};

    setStr(Unc->COFFWeakExternFallbackName, "");

    setStr(Unc->SectionName, "");

    return *Unc;

  };

  SmallString<64> Name;

  {

    raw_svector_ostream OS(Name);

    Msymtab.printSymbolName(OS, Msym);

  }

  setStr(Sym.Name, Saver.save(Name.str()));

  auto Flags = Msymtab.getSymbolFlags(Msym);

  if (Flags & object::BasicSymbolRef::SF_Undefined)

    Sym.Flags |= 1 << storage::Symbol::FB_undefined;

  if (Flags & object::BasicSymbolRef::SF_Weak)

    Sym.Flags |= 1 << storage::Symbol::FB_weak;

  if (Flags & object::BasicSymbolRef::SF_Common)

    Sym.Flags |= 1 << storage::Symbol::FB_common;

  if (Flags & object::BasicSymbolRef::SF_Indirect)

    Sym.Flags |= 1 << storage::Symbol::FB_indirect;

  if (Flags & object::BasicSymbolRef::SF_Global)

    Sym.Flags |= 1 << storage::Symbol::FB_global;

  if (Flags & object::BasicSymbolRef::SF_FormatSpecific)

    Sym.Flags |= 1 << storage::Symbol::FB_format_specific;

  if (Flags & object::BasicSymbolRef::SF_Executable)

    Sym.Flags |= 1 << storage::Symbol::FB_executable;

  Sym.ComdatIndex = -1;

  auto *GV = dyn_cast_if_present<GlobalValue *>(Msym);

  if (!GV) {

    // Undefined module asm symbols act as GC roots and are implicitly used.

    if (Flags & object::BasicSymbolRef::SF_Undefined)

      Sym.Flags |= 1 << storage::Symbol::FB_used;

    setStr(Sym.IRName, "");

    return Error::success();

  }

  setStr(Sym.IRName, GV->getName());

  static const DenseSet<StringRef> PreservedSymbolsSet =

      buildPreservedSymbolsSet();

  bool IsPreservedSymbol = PreservedSymbolsSet.contains(GV->getName());

  if (Used.count(GV) || IsPreservedSymbol)

    Sym.Flags |= 1 << storage::Symbol::FB_used;

  if (GV->isThreadLocal())

    Sym.Flags |= 1 << storage::Symbol::FB_tls;

  if (GV->hasGlobalUnnamedAddr())

    Sym.Flags |= 1 << storage::Symbol::FB_unnamed_addr;

  if (GV->canBeOmittedFromSymbolTable())

    Sym.Flags |= 1 << storage::Symbol::FB_may_omit;

  Sym.Flags |= unsigned(GV->getVisibility()) << storage::Symbol::FB_visibility;

  if (Flags & object::BasicSymbolRef::SF_Common) {

    auto *GVar = dyn_cast<GlobalVariable>(GV);

    if (!GVar)

      return make_error<StringError>("Only variables can have common linkage!",

                                     inconvertibleErrorCode());

    Uncommon().CommonSize =

        GV->getParent()->getDataLayout().getTypeAllocSize(GV->getValueType());

    Uncommon().CommonAlign = GVar->getAlign() ? GVar->getAlign()->value() : 0;

  }

  const GlobalObject *GO = GV->getAliaseeObject();

  if (!GO) {

    if (isa<GlobalIFunc>(GV))

      GO = cast<GlobalIFunc>(GV)->getResolverFunction();

    if (!GO)

      return make_error<StringError>("Unable to determine comdat of alias!",

                                     inconvertibleErrorCode());

  }

  if (const Comdat *C = GO->getComdat()) {

    Expected<int> ComdatIndexOrErr = getComdatIndex(C, GV->getParent());

    if (!ComdatIndexOrErr)

      return ComdatIndexOrErr.takeError();

    Sym.ComdatIndex = *ComdatIndexOrErr;

  }

  if (TT.isOSBinFormatCOFF()) {

    emitLinkerFlagsForGlobalCOFF(COFFLinkerOptsOS, GV, TT, Mang);

    if ((Flags & object::BasicSymbolRef::SF_Weak) &&

        (Flags & object::BasicSymbolRef::SF_Indirect)) {

      auto *Fallback = dyn_cast<GlobalValue>(

          cast<GlobalAlias>(GV)->getAliasee()->stripPointerCasts());

      if (!Fallback)

        return make_error<StringError>("Invalid weak external",

                                       inconvertibleErrorCode());

      std::string FallbackName;

      raw_string_ostream OS(FallbackName);

      Msymtab.printSymbolName(OS, Fallback);

      OS.flush();

      setStr(Uncommon().COFFWeakExternFallbackName, Saver.save(FallbackName));

    }

  }

  if (!GO->getSection().empty())

    setStr(Uncommon().SectionName, Saver.save(GO->getSection()));

  return Error::success();

}

Error Builder::build(ArrayRef<Module *> IRMods) {

  storage::Header Hdr;

  assert(!IRMods.empty());

  Hdr.Version = storage::Header::kCurrentVersion;

  setStr(Hdr.Producer, kExpectedProducerName);

  setStr(Hdr.TargetTriple, IRMods[0]->getTargetTriple());

  setStr(Hdr.SourceFileName, IRMods[0]->getSourceFileName());

  TT = Triple(IRMods[0]->getTargetTriple());

  for (auto *M : IRMods)

    if (Error Err = addModule(M))

      return Err;

  COFFLinkerOptsOS.flush();

  setStr(Hdr.COFFLinkerOpts, Saver.save(COFFLinkerOpts));

  // We are about to fill in the header's range fields, so reserve space for it

  // and copy it in afterwards.

  Symtab.resize(sizeof(storage::Header));

  writeRange(Hdr.Modules, Mods);

  writeRange(Hdr.Comdats, Comdats);

  writeRange(Hdr.Symbols, Syms);

  writeRange(Hdr.Uncommons, Uncommons);

  writeRange(Hdr.DependentLibraries, DependentLibraries);

  *reinterpret_cast<storage::Header *>(Symtab.data()) = Hdr;

  return Error::success();

}

} // end anonymous namespace

Error irsymtab::build(ArrayRef<Module *> Mods, SmallVector<char, 0> &Symtab,

                      StringTableBuilder &StrtabBuilder,

                      BumpPtrAllocator &Alloc) {

  return Builder(Symtab, StrtabBuilder, Alloc).build(Mods);

}

// Upgrade a vector of bitcode modules created by an old version of LLVM by

// creating an irsymtab for them in the current format.

static Expected<FileContents> upgrade(ArrayRef<BitcodeModule> BMs) {

  FileContents FC;

  LLVMContext Ctx;

  std::vector<Module *> Mods;

  std::vector<std::unique_ptr<Module>> OwnedMods;

  for (auto BM : BMs) {

    Expected<std::unique_ptr<Module>> MOrErr =

        BM.getLazyModule(Ctx, /*ShouldLazyLoadMetadata*/ true,

                         /*IsImporting*/ false);

    if (!MOrErr)

      return MOrErr.takeError();

    Mods.push_back(MOrErr->get());

    OwnedMods.push_back(std::move(*MOrErr));

  }

  StringTableBuilder StrtabBuilder(StringTableBuilder::RAW);

  BumpPtrAllocator Alloc;

  if (Error E = build(Mods, FC.Symtab, StrtabBuilder, Alloc))

    return std::move(E);

  StrtabBuilder.finalizeInOrder();

  FC.Strtab.resize(StrtabBuilder.getSize());

  StrtabBuilder.write((uint8_t *)FC.Strtab.data());

  FC.TheReader = {{FC.Symtab.data(), FC.Symtab.size()},

                  {FC.Strtab.data(), FC.Strtab.size()}};

  return std::move(FC);

}

Expected<FileContents> irsymtab::readBitcode(const BitcodeFileContents &BFC) {

  if (BFC.Mods.empty())

    return make_error<StringError>("Bitcode file does not contain any modules",

                                   inconvertibleErrorCode());

  if (!DisableBitcodeVersionUpgrade) {

    if (BFC.StrtabForSymtab.empty() ||

        BFC.Symtab.size() < sizeof(storage::Header))

      return upgrade(BFC.Mods);

    // We cannot use the regular reader to read the version and producer,

    // because it will expect the header to be in the current format. The only

    // thing we can rely on is that the version and producer will be present as

    // the first struct elements.

    auto *Hdr = reinterpret_cast<const storage::Header *>(BFC.Symtab.data());

    unsigned Version = Hdr->Version;

    StringRef Producer = Hdr->Producer.get(BFC.StrtabForSymtab);

    if (Version != storage::Header::kCurrentVersion ||

        Producer != kExpectedProducerName)

      return upgrade(BFC.Mods);

  }

  FileContents FC;

  FC.TheReader = {{BFC.Symtab.data(), BFC.Symtab.size()},

                  {BFC.StrtabForSymtab.data(), BFC.StrtabForSymtab.size()}};

  // Finally, make sure that the number of modules in the symbol table matches

  // the number of modules in the bitcode file. If they differ, it may mean that

  // the bitcode file was created by binary concatenation, so we need to create

  // a new symbol table from scratch.

  if (FC.TheReader.getNumModules() != BFC.Mods.size())

    return upgrade(std::move(BFC.Mods));

  return std::move(FC);

}