static bool Execute()

in lib/LLVMSupport/Support/Unix/Program.inc [176:327]

• 98 lines of code
• 31 McCabe index (conditional complexity)

static bool Execute(ProcessInfo &PI, StringRef Program,
                    ArrayRef<StringRef> Args, Optional<ArrayRef<StringRef>> Env,
                    ArrayRef<Optional<StringRef>> Redirects,
                    unsigned MemoryLimit, std::string *ErrMsg) {
  if (!llvm::sys::fs::exists(Program)) {
    if (ErrMsg)
      *ErrMsg = std::string("Executable \"") + Program.str() +
                std::string("\" doesn't exist!");
    return false;
  }

  BumpPtrAllocator Allocator;
  StringSaver Saver(Allocator);
  std::vector<const char *> ArgVector, EnvVector;
  const char **Argv = nullptr;
  const char **Envp = nullptr;
  ArgVector = toNullTerminatedCStringArray(Args, Saver);
  Argv = ArgVector.data();
  if (Env) {
    EnvVector = toNullTerminatedCStringArray(*Env, Saver);
    Envp = EnvVector.data();
  }

  // If this OS has posix_spawn and there is no memory limit being implied, use
  // posix_spawn.  It is more efficient than fork/exec.
#ifdef HAVE_POSIX_SPAWN
  if (MemoryLimit == 0) {
    posix_spawn_file_actions_t FileActionsStore;
    posix_spawn_file_actions_t *FileActions = nullptr;

    // If we call posix_spawn_file_actions_addopen we have to make sure the
    // c strings we pass to it stay alive until the call to posix_spawn,
    // so we copy any StringRefs into this variable.
    std::string RedirectsStorage[3];

    if (!Redirects.empty()) {
      assert(Redirects.size() == 3);
      std::string *RedirectsStr[3] = {nullptr, nullptr, nullptr};
      for (int I = 0; I < 3; ++I) {
        if (Redirects[I]) {
          RedirectsStorage[I] = *Redirects[I];
          RedirectsStr[I] = &RedirectsStorage[I];
        }
      }

      FileActions = &FileActionsStore;
      posix_spawn_file_actions_init(FileActions);

      // Redirect stdin/stdout.
      if (RedirectIO_PS(RedirectsStr[0], 0, ErrMsg, FileActions) ||
          RedirectIO_PS(RedirectsStr[1], 1, ErrMsg, FileActions))
        return false;
      if (!Redirects[1] || !Redirects[2] || *Redirects[1] != *Redirects[2]) {
        // Just redirect stderr
        if (RedirectIO_PS(RedirectsStr[2], 2, ErrMsg, FileActions))
          return false;
      } else {
        // If stdout and stderr should go to the same place, redirect stderr
        // to the FD already open for stdout.
        if (int Err = posix_spawn_file_actions_adddup2(FileActions, 1, 2))
          return !MakeErrMsg(ErrMsg, "Can't redirect stderr to stdout", Err);
      }
    }

    if (!Envp)
#if !USE_NSGETENVIRON
      Envp = const_cast<const char **>(environ);
#else
      // environ is missing in dylibs.
      Envp = const_cast<const char **>(*_NSGetEnviron());
#endif

    // Explicitly initialized to prevent what appears to be a valgrind false
    // positive.
    pid_t PID = 0;
    int Err = posix_spawn(&PID, Program.str().c_str(), FileActions,
                          /*attrp*/ nullptr, const_cast<char **>(Argv),
                          const_cast<char **>(Envp));

    if (FileActions)
      posix_spawn_file_actions_destroy(FileActions);

    if (Err)
     return !MakeErrMsg(ErrMsg, "posix_spawn failed", Err);

    PI.Pid = PID;
    PI.Process = PID;

    return true;
  }
#endif

  // Create a child process.
  int child = fork();
  switch (child) {
    // An error occurred:  Return to the caller.
    case -1:
      MakeErrMsg(ErrMsg, "Couldn't fork");
      return false;

    // Child process: Execute the program.
    case 0: {
      // Redirect file descriptors...
      if (!Redirects.empty()) {
        // Redirect stdin
        if (RedirectIO(Redirects[0], 0, ErrMsg)) { return false; }
        // Redirect stdout
        if (RedirectIO(Redirects[1], 1, ErrMsg)) { return false; }
        if (Redirects[1] && Redirects[2] && *Redirects[1] == *Redirects[2]) {
          // If stdout and stderr should go to the same place, redirect stderr
          // to the FD already open for stdout.
          if (-1 == dup2(1,2)) {
            MakeErrMsg(ErrMsg, "Can't redirect stderr to stdout");
            return false;
          }
        } else {
          // Just redirect stderr
          if (RedirectIO(Redirects[2], 2, ErrMsg)) { return false; }
        }
      }

      // Set memory limits
      if (MemoryLimit!=0) {
        SetMemoryLimits(MemoryLimit);
      }

      // Execute!
      std::string PathStr = Program;
      if (Envp != nullptr)
        execve(PathStr.c_str(), const_cast<char **>(Argv),
               const_cast<char **>(Envp));
      else
        execv(PathStr.c_str(), const_cast<char **>(Argv));
      // If the execve() failed, we should exit. Follow Unix protocol and
      // return 127 if the executable was not found, and 126 otherwise.
      // Use _exit rather than exit so that atexit functions and static
      // object destructors cloned from the parent process aren't
      // redundantly run, and so that any data buffered in stdio buffers
      // cloned from the parent aren't redundantly written out.
      _exit(errno == ENOENT ? 127 : 126);
    }

    // Parent process: Break out of the switch to do our processing.
    default:
      break;
  }

  PI.Pid = child;
  PI.Process = child;

  return true;
}