lld/COFF/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 "Config.h"
#include "Driver.h"
#include "InputFiles.h"
#include "Memory.h"
#include "SymbolTable.h"
#include "Writer.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/Option/Arg.h"
#include "llvm/Option/ArgList.h"
#include "llvm/Option/Option.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/Process.h"
#include "llvm/Support/TargetSelect.h"
#include "llvm/Support/raw_ostream.h"
#include <memory>

using namespace llvm;
using llvm::COFF::IMAGE_SUBSYSTEM_UNKNOWN;
using llvm::COFF::IMAGE_SUBSYSTEM_WINDOWS_CUI;
using llvm::COFF::IMAGE_SUBSYSTEM_WINDOWS_GUI;
using llvm::sys::Process;
using llvm::sys::fs::file_magic;
using llvm::sys::fs::identify_magic;

namespace lld {
namespace coff {

Configuration *Config;
LinkerDriver *Driver;

bool link(int Argc, const char *Argv[]) {
  auto C = make_unique<Configuration>();
  Config = C.get();
  auto D = make_unique<LinkerDriver>();
  Driver = D.get();
  return Driver->link(Argc, Argv);
}

static std::string getOutputPath(llvm::opt::InputArgList *Args) {
  if (auto *Arg = Args->getLastArg(OPT_out))
    return Arg->getValue();
  for (auto *Arg : Args->filtered(OPT_INPUT)) {
    if (!StringRef(Arg->getValue()).endswith_lower(".obj"))
      continue;
    SmallString<128> Val = StringRef(Arg->getValue());
    llvm::sys::path::replace_extension(Val, ".exe");
    return Val.str();
  }
  llvm_unreachable("internal error");
}

// Opens a file. Path has to be resolved already.
// Newly created memory buffers are owned by this driver.
ErrorOr<std::unique_ptr<InputFile>> LinkerDriver::openFile(StringRef Path) {
  auto MBOrErr = MemoryBuffer::getFile(Path);
  if (auto EC = MBOrErr.getError())
    return EC;
  std::unique_ptr<MemoryBuffer> MB = std::move(MBOrErr.get());
  MemoryBufferRef MBRef = MB->getMemBufferRef();
  OwningMBs.push_back(std::move(MB)); // take ownership

  // File type is detected by contents, not by file extension.
  file_magic Magic = identify_magic(MBRef.getBuffer());
  if (Magic == file_magic::archive)
    return std::unique_ptr<InputFile>(new ArchiveFile(MBRef));
  if (Magic == file_magic::bitcode)
    return std::unique_ptr<InputFile>(new BitcodeFile(MBRef));
  return std::unique_ptr<InputFile>(new ObjectFile(MBRef));
}

namespace {
class BumpPtrStringSaver : public llvm::cl::StringSaver {
public:
  BumpPtrStringSaver(lld::coff::StringAllocator *A) : Alloc(A) {}
  const char *SaveString(const char *S) override {
    return Alloc->save(S).data();
  }
  lld::coff::StringAllocator *Alloc;
};
}

// Parses .drectve section contents and returns a list of files
// specified by /defaultlib.
std::error_code
LinkerDriver::parseDirectives(StringRef S,
                              std::vector<std::unique_ptr<InputFile>> *Res) {
  SmallVector<const char *, 16> Tokens;
  Tokens.push_back("link"); // argv[0] value. Will be ignored.
  BumpPtrStringSaver Saver(&Alloc);
  llvm::cl::TokenizeWindowsCommandLine(S, Saver, Tokens);
  Tokens.push_back(nullptr);
  int Argc = Tokens.size() - 1;
  const char **Argv = &Tokens[0];

  auto ArgsOrErr = parseArgs(Argc, Argv);
  if (auto EC = ArgsOrErr.getError())
    return EC;
  std::unique_ptr<llvm::opt::InputArgList> Args = std::move(ArgsOrErr.get());

  for (auto *Arg : Args->filtered(OPT_defaultlib)) {
    if (Optional<StringRef> Path = findLib(Arg->getValue())) {
      auto FileOrErr = openFile(*Path);
      if (auto EC = FileOrErr.getError())
        return EC;
      std::unique_ptr<InputFile> File = std::move(FileOrErr.get());
      Res->push_back(std::move(File));
    }
  }
  return std::error_code();
}

// Find file from search paths. You can omit ".obj", this function takes
// care of that. Note that the returned path is not guaranteed to exist.
StringRef LinkerDriver::doFindFile(StringRef Filename) {
  bool hasPathSep = (Filename.find_first_of("/\\") != StringRef::npos);
  if (hasPathSep)
    return Filename;
  bool hasExt = (Filename.find('.') != StringRef::npos);
  for (StringRef Dir : SearchPaths) {
    SmallString<128> Path = Dir;
    llvm::sys::path::append(Path, Filename);
    if (llvm::sys::fs::exists(Path.str()))
      return Alloc.save(Path.str());
    if (!hasExt) {
      Path.append(".obj");
      if (llvm::sys::fs::exists(Path.str()))
        return Alloc.save(Path.str());
    }
  }
  return Filename;
}

// Resolves a file path. This never returns the same path
// (in that case, it returns None).
Optional<StringRef> LinkerDriver::findFile(StringRef Filename) {
  StringRef Path = doFindFile(Filename);
  bool Seen = !VisitedFiles.insert(Path.lower()).second;
  if (Seen)
    return None;
  return Path;
}

// Find library file from search path.
StringRef LinkerDriver::doFindLib(StringRef Filename) {
  // Add ".lib" to Filename if that has no file extension.
  bool hasExt = (Filename.find('.') != StringRef::npos);
  if (!hasExt)
    Filename = Alloc.save(Filename + ".lib");
  return doFindFile(Filename);
}

// Resolves a library path. /nodefaultlib options are taken into
// consideration. This never returns the same path (in that case,
// it returns None).
Optional<StringRef> LinkerDriver::findLib(StringRef Filename) {
  if (Config->NoDefaultLibAll)
    return None;
  StringRef Path = doFindLib(Filename);
  if (Config->NoDefaultLibs.count(Path))
    return None;
  bool Seen = !VisitedFiles.insert(Path.lower()).second;
  if (Seen)
    return None;
  return Path;
}

// Parses LIB environment which contains a list of search paths.
std::vector<StringRef> LinkerDriver::getSearchPaths() {
  std::vector<StringRef> Ret;
  Ret.push_back(".");
  Optional<std::string> EnvOpt = Process::GetEnv("LIB");
  if (!EnvOpt.hasValue())
    return Ret;
  StringRef Env = Alloc.save(*EnvOpt);
  while (!Env.empty()) {
    StringRef Path;
    std::tie(Path, Env) = Env.split(';');
    Ret.push_back(Path);
  }
  return Ret;
}

bool LinkerDriver::link(int Argc, const char *Argv[]) {
  // Needed for LTO.
  llvm::InitializeAllTargetInfos();
  llvm::InitializeAllTargets();
  llvm::InitializeAllTargetMCs();
  llvm::InitializeAllAsmParsers();
  llvm::InitializeAllAsmPrinters();
  llvm::InitializeAllDisassemblers();

  // Parse command line options.
  auto ArgsOrErr = parseArgs(Argc, Argv);
  if (auto EC = ArgsOrErr.getError()) {
    llvm::errs() << EC.message() << "\n";
    return false;
  }
  std::unique_ptr<llvm::opt::InputArgList> Args = std::move(ArgsOrErr.get());

  // Handle /help
  if (Args->hasArg(OPT_help)) {
    printHelp(Argv[0]);
    return true;
  }

  if (Args->filtered_begin(OPT_INPUT) == Args->filtered_end()) {
    llvm::errs() << "no input files.\n";
    return false;
  }

  // Handle /verbose
  if (Args->hasArg(OPT_verbose))
    Config->Verbose = true;

  // Handle /entry
  if (auto *Arg = Args->getLastArg(OPT_entry))
    Config->EntryName = Arg->getValue();

  // Handle /machine
  auto MTOrErr = getMachineType(Args.get());
  if (auto EC = MTOrErr.getError()) {
    llvm::errs() << EC.message() << "\n";
    return false;
  }
  Config->MachineType = MTOrErr.get();

  // Handle /libpath
  for (auto *Arg : Args->filtered(OPT_libpath)) {
    // Inserting at front of a vector is okay because it's short.
    // +1 because the first entry is always "." (current directory).
    SearchPaths.insert(SearchPaths.begin() + 1, Arg->getValue());
  }

  // Handle /nodefaultlib:<filename>
  for (auto *Arg : Args->filtered(OPT_nodefaultlib))
    Config->NoDefaultLibs.insert(doFindLib(Arg->getValue()));

  // Handle /nodefaultlib
  if (Args->hasArg(OPT_nodefaultlib_all))
    Config->NoDefaultLibAll = true;

  // Handle /base
  if (auto *Arg = Args->getLastArg(OPT_base)) {
    if (auto EC = parseNumbers(Arg->getValue(), &Config->ImageBase)) {
      llvm::errs() << "/base: " << EC.message() << "\n";
      return false;
    }
  }

  // Handle /stack
  if (auto *Arg = Args->getLastArg(OPT_stack)) {
    if (auto EC = parseNumbers(Arg->getValue(), &Config->StackReserve,
                               &Config->StackCommit)) {
      llvm::errs() << "/stack: " << EC.message() << "\n";
      return false;
    }
  }

  // Handle /heap
  if (auto *Arg = Args->getLastArg(OPT_heap)) {
    if (auto EC = parseNumbers(Arg->getValue(), &Config->HeapReserve,
                               &Config->HeapCommit)) {
      llvm::errs() << "/heap: " << EC.message() << "\n";
      return false;
    }
  }

  // Handle /version
  if (auto *Arg = Args->getLastArg(OPT_version)) {
    if (auto EC = parseVersion(Arg->getValue(), &Config->MajorImageVersion,
                               &Config->MinorImageVersion)) {
      llvm::errs() << "/version: " << EC.message() << "\n";
      return false;
    }
  }

  // Handle /subsystem
  if (auto *Arg = Args->getLastArg(OPT_subsystem)) {
    if (auto EC = parseSubsystem(Arg->getValue(), &Config->Subsystem,
                                 &Config->MajorOSVersion,
                                 &Config->MinorOSVersion)) {
      llvm::errs() << "/subsystem: " << EC.message() << "\n";
      return false;
    }
  }

  // Create a list of input files. Files can be given as arguments
  // for /defaultlib option.
  std::vector<StringRef> Inputs;
  for (auto *Arg : Args->filtered(OPT_INPUT))
    if (Optional<StringRef> Path = findFile(Arg->getValue()))
      Inputs.push_back(*Path);
  for (auto *Arg : Args->filtered(OPT_defaultlib))
    if (Optional<StringRef> Path = findLib(Arg->getValue()))
      Inputs.push_back(*Path);

  // Create a symbol table.
  SymbolTable Symtab;

  // Add undefined symbols given via the command line.
  // (/include is equivalent to Unix linker's -u option.)
  for (auto *Arg : Args->filtered(OPT_incl)) {
    StringRef Sym = Arg->getValue();
    Symtab.addUndefined(Sym);
    Config->GCRoots.insert(Sym);
  }

  // Parse all input files and put all symbols to the symbol table.
  // The symbol table will take care of name resolution.
  for (StringRef Path : Inputs) {
    auto FileOrErr = openFile(Path);
    if (auto EC = FileOrErr.getError()) {
      llvm::errs() << Path << ": " << EC.message() << "\n";
      return false;
    }
    std::unique_ptr<InputFile> File = std::move(FileOrErr.get());
    if (auto EC = Symtab.addFile(std::move(File))) {
      llvm::errs() << Path << ": " << EC.message() << "\n";
      return false;
    }
  }

  // Add weak aliases. Weak aliases is a mechanism to give remaining
  // undefined symbols final chance to be resolved successfully.
  // This is symbol renaming.
  for (auto *Arg : Args->filtered(OPT_alternatename)) {
    StringRef From, To;
    std::tie(From, To) = StringRef(Arg->getValue()).split('=');
    if (From.empty() || To.empty()) {
      llvm::errs() << "/alternatename: invalid argument: "
                   << Arg->getValue() << "\n";
      return false;
    }
    // If it's already resolved as some Defined type, do nothing.
    // Otherwise, rename it to see if To can be resolved instead.
    if (Symtab.find(From))
      continue;
    if (auto EC = Symtab.rename(From, To)) {
      llvm::errs() << EC.message() << "\n";
      return false;
    }
  }

  // Windows specific -- If entry point name is not given, we need to
  // infer that from user-defined entry name. The symbol table takes
  // care of details.
  if (Config->EntryName.empty()) {
    auto EntryOrErr = Symtab.findDefaultEntry();
    if (auto EC = EntryOrErr.getError()) {
      llvm::errs() << EC.message() << "\n";
      return false;
    }
    Config->EntryName = EntryOrErr.get();
  }
  Config->GCRoots.insert(Config->EntryName);

  // Make sure we have resolved all symbols.
  if (Symtab.reportRemainingUndefines())
    return false;

  // Do LTO by compiling bitcode input files to a native COFF file
  // then link that file.
  if (auto EC = Symtab.addCombinedLTOObject()) {
    llvm::errs() << EC.message() << "\n";
    return false;
  }

  // /include option takes precedence over garbage collection.
  for (auto *Arg : Args->filtered(OPT_incl))
    Symtab.find(Arg->getValue())->markLive();

  // Windows specific -- if no /subsystem is given, we need to infer
  // that from entry point name.
  if (Config->Subsystem == IMAGE_SUBSYSTEM_UNKNOWN) {
    Config->Subsystem =
      StringSwitch<WindowsSubsystem>(Config->EntryName)
          .Case("mainCRTStartup", IMAGE_SUBSYSTEM_WINDOWS_CUI)
          .Case("wmainCRTStartup", IMAGE_SUBSYSTEM_WINDOWS_CUI)
          .Case("WinMainCRTStartup", IMAGE_SUBSYSTEM_WINDOWS_GUI)
          .Case("wWinMainCRTStartup", IMAGE_SUBSYSTEM_WINDOWS_GUI)
          .Default(IMAGE_SUBSYSTEM_UNKNOWN);
    if (Config->Subsystem == IMAGE_SUBSYSTEM_UNKNOWN) {
      llvm::errs() << "subsystem must be defined\n";
      return false;
    }
  }

  // Write the result.
  Writer Out(&Symtab);
  if (auto EC = Out.write(getOutputPath(Args.get()))) {
    llvm::errs() << EC.message() << "\n";
    return false;
  }
  return true;
}

} // namespace coff
} // namespace lld