lld/ELF/Driver.cpp

//===- Driver.cpp ---------------------------------------------------------===//
//
//                             The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "Driver.h"
#include "Config.h"
#include "Error.h"
#include "InputFiles.h"
#include "SymbolTable.h"
#include "Target.h"
#include "Writer.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/Support/raw_ostream.h"
#include <utility>

using namespace llvm;
using namespace llvm::ELF;
using namespace llvm::object;

using namespace lld;
using namespace lld::elf2;

Configuration *lld::elf2::Config;
LinkerDriver *lld::elf2::Driver;

void lld::elf2::link(ArrayRef<const char *> Args) {
  Configuration C;
  LinkerDriver D;
  Config = &C;
  Driver = &D;
  Driver->main(Args.slice(1));
}

static std::pair<ELFKind, uint16_t> parseEmulation(StringRef S) {
  Config->Emulation = S;
  if (S == "elf32btsmip")
    return {ELF32BEKind, EM_MIPS};
  if (S == "elf32ltsmip")
    return {ELF32LEKind, EM_MIPS};
  if (S == "elf32ppc")
    return {ELF32BEKind, EM_PPC};
  if (S == "elf64ppc")
    return {ELF64BEKind, EM_PPC64};
  if (S == "elf_i386")
    return {ELF32LEKind, EM_386};
  if (S == "elf_x86_64")
    return {ELF64LEKind, EM_X86_64};
  error("Unknown emulation: " + S);
}

// Opens and parses a file. Path has to be resolved already.
// Newly created memory buffers are owned by this driver.
void LinkerDriver::addFile(StringRef Path) {
  using namespace llvm::sys::fs;
  if (Config->Verbose)
    llvm::outs() << Path << "\n";
  auto MBOrErr = MemoryBuffer::getFile(Path);
  error(MBOrErr, "cannot open " + Path);
  std::unique_ptr<MemoryBuffer> &MB = *MBOrErr;
  MemoryBufferRef MBRef = MB->getMemBufferRef();
  OwningMBs.push_back(std::move(MB)); // take MB ownership

  switch (identify_magic(MBRef.getBuffer())) {
  case file_magic::unknown:
    readLinkerScript(&Alloc, MBRef);
    return;
  case file_magic::archive:
    if (WholeArchive) {
      auto File = make_unique<ArchiveFile>(MBRef);
      for (MemoryBufferRef &MB : File->getMembers())
        Files.push_back(createELFFile<ObjectFile>(MB));
      OwningArchives.emplace_back(std::move(File));
      return;
    }
    Files.push_back(make_unique<ArchiveFile>(MBRef));
    return;
  case file_magic::elf_shared_object:
    Files.push_back(createELFFile<SharedFile>(MBRef));
    return;
  default:
    Files.push_back(createELFFile<ObjectFile>(MBRef));
  }
}

static StringRef
getString(opt::InputArgList &Args, unsigned Key, StringRef Default = "") {
  if (auto *Arg = Args.getLastArg(Key))
    return Arg->getValue();
  return Default;
}

void LinkerDriver::main(ArrayRef<const char *> ArgsArr) {
  initSymbols();

  opt::InputArgList Args = parseArgs(&Alloc, ArgsArr);
  createFiles(Args);

  switch (Config->EKind) {
  case ELF32LEKind:
    link<ELF32LE>(Args);
    return;
  case ELF32BEKind:
    link<ELF32BE>(Args);
    return;
  case ELF64LEKind:
    link<ELF64LE>(Args);
    return;
  case ELF64BEKind:
    link<ELF64BE>(Args);
    return;
  default:
    error("-m or at least a .o file required");
  }
}

void LinkerDriver::createFiles(opt::InputArgList &Args) {
  for (auto *Arg : Args.filtered(OPT_L))
    Config->SearchPaths.push_back(Arg->getValue());

  std::vector<StringRef> RPaths;
  for (auto *Arg : Args.filtered(OPT_rpath))
    RPaths.push_back(Arg->getValue());
  if (!RPaths.empty())
    Config->RPath = llvm::join(RPaths.begin(), RPaths.end(), ":");

  if (auto *Arg = Args.getLastArg(OPT_m)) {
    std::pair<ELFKind, uint16_t> P = parseEmulation(Arg->getValue());
    Config->EKind = P.first;
    Config->EMachine = P.second;
  }

  Config->AllowMultipleDefinition = Args.hasArg(OPT_allow_multiple_definition);
  Config->DiscardAll = Args.hasArg(OPT_discard_all);
  Config->DiscardLocals = Args.hasArg(OPT_discard_locals);
  Config->DiscardNone = Args.hasArg(OPT_discard_none);
  Config->EnableNewDtags = !Args.hasArg(OPT_disable_new_dtags);
  Config->ExportDynamic = Args.hasArg(OPT_export_dynamic);
  Config->NoInhibitExec = Args.hasArg(OPT_noinhibit_exec);
  Config->NoUndefined = Args.hasArg(OPT_no_undefined);
  Config->Shared = Args.hasArg(OPT_shared);
  Config->Verbose = Args.hasArg(OPT_verbose);

  Config->DynamicLinker = getString(Args, OPT_dynamic_linker);
  Config->Entry = getString(Args, OPT_entry);
  Config->Fini = getString(Args, OPT_fini, "_fini");
  Config->Init = getString(Args, OPT_init, "_init");
  Config->OutputFile = getString(Args, OPT_o);
  Config->SoName = getString(Args, OPT_soname);
  Config->Sysroot = getString(Args, OPT_sysroot);

  for (auto *Arg : Args.filtered(OPT_z))
    if (Arg->getValue() == StringRef("now"))
      Config->ZNow = true;

  for (auto *Arg : Args) {
    switch (Arg->getOption().getID()) {
    case OPT_l:
      addFile(searchLibrary(Arg->getValue()));
      break;
    case OPT_INPUT:
    case OPT_script:
      addFile(Arg->getValue());
      break;
    case OPT_as_needed:
      Config->AsNeeded = true;
      break;
    case OPT_no_as_needed:
      Config->AsNeeded = false;
      break;
    case OPT_Bstatic:
      Config->Static = true;
      break;
    case OPT_Bdynamic:
      Config->Static = false;
      break;
    case OPT_whole_archive:
      WholeArchive = true;
      break;
    case OPT_no_whole_archive:
      WholeArchive = false;
      break;
    }
  }

  if (Files.empty())
    error("no input files.");
}

template <class ELFT> void LinkerDriver::link(opt::InputArgList &Args) {
  SymbolTable<ELFT> Symtab;
  Target.reset(createTarget());

  if (!Config->Shared) {
    // Add entry symbol.
    if (Config->Entry.empty())
      Config->Entry = (Config->EMachine == EM_MIPS) ? "__start" : "_start";
    Config->EntrySym = Symtab.addUndefined(Config->Entry);

    // In the assembly for 32 bit x86 the _GLOBAL_OFFSET_TABLE_ symbol
    // is magical and is used to produce a R_386_GOTPC relocation.
    // The R_386_GOTPC relocation value doesn't actually depend on the
    // symbol value, so it could use an index of STN_UNDEF which, according
    // to the spec, means the symbol value is 0.
    // Unfortunately both gas and MC keep the _GLOBAL_OFFSET_TABLE_ symbol in
    // the object file.
    // The situation is even stranger on x86_64 where the assembly doesn't
    // need the magical symbol, but gas still puts _GLOBAL_OFFSET_TABLE_ as
    // an undefined symbol in the .o files.
    // Given that the symbol is effectively unused, we just create a dummy
    // hidden one to avoid the undefined symbol error.
    Symtab.addIgnoredSym("_GLOBAL_OFFSET_TABLE_");
  }

  for (std::unique_ptr<InputFile> &F : Files)
    Symtab.addFile(std::move(F));

  for (auto *Arg : Args.filtered(OPT_undefined))
    Symtab.addUndefinedOpt(Arg->getValue());

  if (Config->OutputFile.empty())
    Config->OutputFile = "a.out";

  // Write the result to the file.
  writeResult<ELFT>(&Symtab);
}