Function vfork

src/execwrappers.cpp:233–308

static void* newStackAddr;

extern "C" pid_t
vfork()
{
  JTRACE("Simulating vfork with fork");
  return fork();

  char dummy;
  static __typeof__(&vfork) vforkPtr =
    (__typeof__(&vfork)) dmtcp_dlsym(RTLD_NEXT, "vfork");

  JASSERT (!isPerformingCkptRestart());

  ThreadSync::presuspendEventHookLockLock();

  /* Acquire all locks here. */
  ThreadSync::acquireLocks();

  ThreadList::vforkSuspendThreads();

  PluginManager::eventHook(DMTCP_EVENT_VFORK_PREPARE, NULL);

  // Save the contents of the current call frame before calling libc:vfork. The
  // vfork syscall won't return in the parent until the child process has either
  // exited or exec'd. In both cases, the current call frame on stack will
  // most-likely get overwritten by the child process. (The call frames below
  // the current call-frame are expected to be safe as the child process is not
  // expected to return from the current call frame).
  // Failure to restore the current call frame in the parent might result in
  // lost $RBP data that include the return address.
  //
  // NOTE: The vfork wrapper in pid_miscwrappers.cpp performs similar
  // save/restore of the current call frame. This duplication is required in
  // case we decide to not use the PID plugin.
  //
  // TODO: Deduplicate stack save/restore with similar code in
  // execwrappers.cpp's vfork wrapper.
  stackStart = &dummy;
  // Return address is stored at $rbp + sizeof($rbp) + sizeof(void*)
  stackSize =
    (char*) __builtin_frame_address(0) + (2 * sizeof(void*)) - stackStart;
  newStackAddr = JALLOC_MALLOC(stackSize);
  JASSERT(newStackAddr);
  memcpy(newStackAddr, stackStart, stackSize);

  vforkPid = vforkPtr();

  // Restore parent stack.
  if (vforkPid > 0) {
    memcpy(stackStart, newStackAddr, stackSize);
    JALLOC_FREE(newStackAddr);
  }

  ThreadSync::resetLocks(false);

  if (vforkPid == -1) {
    PluginManager::eventHook(DMTCP_EVENT_VFORK_FAILED, NULL);
    JTRACE("vfork failed") (vforkPid);
  } else if (vforkPid == 0) { /* child process */