linux-low.c

这个是LINUX下的GDB调度工具的源码

	      remove_inferior (&all_processes, &event_child->head);
	      free (event_child);
	      remove_thread (current_inferior);
	      current_inferior = (struct thread_info *) all_threads.head;

	      /* If we were waiting for this particular child to do something...
		 well, it did something.  */
	      if (child != NULL)
		return wstat;

	      /* Wait for a more interesting event.  */
	      continue;
	    }

	  if (WIFSTOPPED (wstat)
	      && WSTOPSIG (wstat) == SIGSTOP
	      && event_child->stop_expected)
	    {
	      if (debug_threads)
		fprintf (stderr, "Expected stop.\n");
	      event_child->stop_expected = 0;
	      linux_resume_one_process (&event_child->head,
					event_child->stepping, 0);
	      continue;
	    }

	  /* FIXME drow/2002-06-09: Get signal numbers from the inferior's
	     thread library?  */
	  if (WIFSTOPPED (wstat)
	      && (WSTOPSIG (wstat) == __SIGRTMIN
		  || WSTOPSIG (wstat) == __SIGRTMIN + 1))
	    {
	      if (debug_threads)
		fprintf (stderr, "Ignored signal %d for %d (LWP %d).\n",
			 WSTOPSIG (wstat), event_child->tid,
			 event_child->head.id);
	      linux_resume_one_process (&event_child->head,
					event_child->stepping,
					WSTOPSIG (wstat));
	      continue;
	    }
	}

      /* If this event was not handled above, and is not a SIGTRAP, report
	 it.  */
      if (!WIFSTOPPED (wstat) || WSTOPSIG (wstat) != SIGTRAP)
	return wstat;

      /* If this target does not support breakpoints, we simply report the
	 SIGTRAP; it's of no concern to us.  */
      if (the_low_target.get_pc == NULL)
	return wstat;

      stop_pc = get_stop_pc ();

      /* bp_reinsert will only be set if we were single-stepping.
	 Notice that we will resume the process after hitting
	 a gdbserver breakpoint; single-stepping to/over one
	 is not supported (yet).  */
      if (event_child->bp_reinsert != 0)
	{
	  if (debug_threads)
	    fprintf (stderr, "Reinserted breakpoint.\n");
	  reinsert_breakpoint (event_child->bp_reinsert);
	  event_child->bp_reinsert = 0;

	  /* Clear the single-stepping flag and SIGTRAP as we resume.  */
	  linux_resume_one_process (&event_child->head, 0, 0);
	  continue;
	}

      if (debug_threads)
	fprintf (stderr, "Hit a (non-reinsert) breakpoint.\n");

      if (check_breakpoints (stop_pc) != 0)
	{
	  /* We hit one of our own breakpoints.  We mark it as a pending
	     breakpoint, so that check_removed_breakpoint () will do the PC
	     adjustment for us at the appropriate time.  */
	  event_child->pending_is_breakpoint = 1;
	  event_child->pending_stop_pc = stop_pc;

	  /* Now we need to put the breakpoint back.  We continue in the event
	     loop instead of simply replacing the breakpoint right away,
	     in order to not lose signals sent to the thread that hit the
	     breakpoint.  Unfortunately this increases the window where another
	     thread could sneak past the removed breakpoint.  For the current
	     use of server-side breakpoints (thread creation) this is
	     acceptable; but it needs to be considered before this breakpoint
	     mechanism can be used in more general ways.  For some breakpoints
	     it may be necessary to stop all other threads, but that should
	     be avoided where possible.

	     If breakpoint_reinsert_addr is NULL, that means that we can
	     use PTRACE_SINGLESTEP on this platform.  Uninsert the breakpoint,
	     mark it for reinsertion, and single-step.

	     Otherwise, call the target function to figure out where we need
	     our temporary breakpoint, create it, and continue executing this
	     process.  */
	  if (the_low_target.breakpoint_reinsert_addr == NULL)
	    {
	      event_child->bp_reinsert = stop_pc;
	      uninsert_breakpoint (stop_pc);
	      linux_resume_one_process (&event_child->head, 1, 0);
	    }
	  else
	    {
	      reinsert_breakpoint_by_bp
		(stop_pc, (*the_low_target.breakpoint_reinsert_addr) ());
	      linux_resume_one_process (&event_child->head, 0, 0);
	    }

	  continue;
	}

      /* If we were single-stepping, we definitely want to report the
	 SIGTRAP.  The single-step operation has completed, so also
         clear the stepping flag; in general this does not matter,
	 because the SIGTRAP will be reported to the client, which
	 will give us a new action for this thread, but clear it for
	 consistency anyway.  It's safe to clear the stepping flag
         because the only consumer of get_stop_pc () after this point
	 is check_removed_breakpoint, and pending_is_breakpoint is not
	 set.  It might be wiser to use a step_completed flag instead.  */
      if (event_child->stepping)
	{
	  event_child->stepping = 0;
	  return wstat;
	}

      /* A SIGTRAP that we can't explain.  It may have been a breakpoint.
	 Check if it is a breakpoint, and if so mark the process information
	 accordingly.  This will handle both the necessary fiddling with the
	 PC on decr_pc_after_break targets and suppressing extra threads
	 hitting a breakpoint if two hit it at once and then GDB removes it
	 after the first is reported.  Arguably it would be better to report
	 multiple threads hitting breakpoints simultaneously, but the current
	 remote protocol does not allow this.  */
      if ((*the_low_target.breakpoint_at) (stop_pc))
	{
	  event_child->pending_is_breakpoint = 1;
	  event_child->pending_stop_pc = stop_pc;
	}

      return wstat;
    }

  /* NOTREACHED */
  return 0;
}

/* Wait for process, returns status.  */

static unsigned char
linux_wait (char *status)
{
  int w;
  struct thread_info *child = NULL;

retry:
  /* If we were only supposed to resume one thread, only wait for
     that thread - if it's still alive.  If it died, however - which
     can happen if we're coming from the thread death case below -
     then we need to make sure we restart the other threads.  We could
     pick a thread at random or restart all; restarting all is less
     arbitrary.  */
  if (cont_thread > 0)
    {
      child = (struct thread_info *) find_inferior_id (&all_threads,
						       cont_thread);

      /* No stepping, no signal - unless one is pending already, of course.  */
      if (child == NULL)
	{
	  struct thread_resume resume_info;
	  resume_info.thread = -1;
	  resume_info.step = resume_info.sig = resume_info.leave_stopped = 0;
	  linux_resume (&resume_info);
	}
    }

  enable_async_io ();
  unblock_async_io ();
  w = linux_wait_for_event (child);
  stop_all_processes ();
  disable_async_io ();

  /* If we are waiting for a particular child, and it exited,
     linux_wait_for_event will return its exit status.  Similarly if
     the last child exited.  If this is not the last child, however,
     do not report it as exited until there is a 'thread exited' response
     available in the remote protocol.  Instead, just wait for another event.
     This should be safe, because if the thread crashed we will already
     have reported the termination signal to GDB; that should stop any
     in-progress stepping operations, etc.

     Report the exit status of the last thread to exit.  This matches
     LinuxThreads' behavior.  */

  if (all_threads.head == all_threads.tail)
    {
      if (WIFEXITED (w))
	{
	  fprintf (stderr, "\nChild exited with retcode = %x \n", WEXITSTATUS (w));
	  *status = 'W';
	  clear_inferiors ();
	  free (all_processes.head);
	  all_processes.head = all_processes.tail = NULL;
	  return ((unsigned char) WEXITSTATUS (w));
	}
      else if (!WIFSTOPPED (w))
	{
	  fprintf (stderr, "\nChild terminated with signal = %x \n", WTERMSIG (w));
	  *status = 'X';
	  clear_inferiors ();
	  free (all_processes.head);
	  all_processes.head = all_processes.tail = NULL;
	  return ((unsigned char) WTERMSIG (w));
	}
    }
  else
    {
      if (!WIFSTOPPED (w))
	goto retry;
    }

  *status = 'T';
  return ((unsigned char) WSTOPSIG (w));
}

/* Send a signal to an LWP.  For LinuxThreads, kill is enough; however, if
   thread groups are in use, we need to use tkill.  */

static int
kill_lwp (int lwpid, int signo)
{
  static int tkill_failed;

  errno = 0;

#ifdef SYS_tkill
  if (!tkill_failed)
    {
      int ret = syscall (SYS_tkill, lwpid, signo);
      if (errno != ENOSYS)
        return ret;
      errno = 0;
      tkill_failed = 1;
    }
#endif

  return kill (lwpid, signo);
}

static void
send_sigstop (struct inferior_list_entry *entry)
{
  struct process_info *process = (struct process_info *) entry;

  if (process->stopped)
    return;

  /* If we already have a pending stop signal for this process, don't
     send another.  */
  if (process->stop_expected)
    {
      process->stop_expected = 0;
      return;
    }

  if (debug_threads)
    fprintf (stderr, "Sending sigstop to process %d\n", process->head.id);

  kill_lwp (process->head.id, SIGSTOP);
  process->sigstop_sent = 1;
}

static void
wait_for_sigstop (struct inferior_list_entry *entry)
{
  struct process_info *process = (struct process_info *) entry;
  struct thread_info *saved_inferior, *thread;
  int wstat, saved_tid;

  if (process->stopped)
    return;

  saved_inferior = current_inferior;
  saved_tid = ((struct inferior_list_entry *) saved_inferior)->id;
  thread = (struct thread_info *) find_inferior_id (&all_threads,
						    process->tid);
  wstat = linux_wait_for_event (thread);

  /* If we stopped with a non-SIGSTOP signal, save it for later
     and record the pending SIGSTOP.  If the process exited, just
     return.  */
  if (WIFSTOPPED (wstat)
      && WSTOPSIG (wstat) != SIGSTOP)
    {
      if (debug_threads)
	fprintf (stderr, "Stopped with non-sigstop signal\n");
      process->status_pending_p = 1;
      process->status_pending = wstat;
      process->stop_expected = 1;
    }

  if (linux_thread_alive (saved_tid))
    current_inferior = saved_inferior;
  else
    {
      if (debug_threads)
	fprintf (stderr, "Previously current thread died.\n");

      /* Set a valid thread as current.  */
      set_desired_inferior (0);
    }
}

static void
stop_all_processes (void)
{
  stopping_threads = 1;
  for_each_inferior (&all_processes, send_sigstop);
  for_each_inferior (&all_processes, wait_for_sigstop);
  stopping_threads = 0;
}

/* Resume execution of the inferior process.
   If STEP is nonzero, single-step it.
   If SIGNAL is nonzero, give it that signal.  */

static void
linux_resume_one_process (struct inferior_list_entry *entry,
			  int step, int signal)
{
  struct process_info *process = (struct process_info *) entry;
  struct thread_info *saved_inferior;

  if (process->stopped == 0)
    return;

  /* If we have pending signals or status, and a new signal, enqueue the
     signal.  Also enqueue the signal if we are waiting to reinsert a
     breakpoint; it will be picked up again below.  */
  if (signal != 0
      && (process->status_pending_p || process->pending_signals != NULL
	  || process->bp_reinsert != 0))
    {
      struct pending_signals *p_sig;
      p_sig = malloc (sizeof (*p_sig));
      p_sig->prev = process->pending_signals;
      p_sig->signal = signal;
      process->pending_signals = p_sig;
    }

  if (process->status_pending_p && !check_removed_breakpoint (process))
    return;

  saved_inferior = current_inferior;
  current_inferior = get_process_thread (process);

  if (debug_threads)
    fprintf (stderr, "Resuming process %d (%s, signal %d, stop %s)\n", inferior_pid,
	     step ? "step" : "continue", signal,
	     process->stop_expected ? "expected" : "not expected");

  /* This bit needs some thinking about.  If we get a signal that
     we must report while a single-step reinsert is still pending,
     we often end up resuming the thread.  It might be better to
     (ew) allow a stack of pending events; then we could be sure that
     the reinsert happened right away and not lose any signals.

     Making this stack would also shrink the window in which breakpoints are
     uninserted (see comment in linux_wait_for_process) but not enough for
     complete correctness, so it won't solve that problem.  It may be
     worthwhile just to solve this one, however.  */
  if (process->bp_reinsert != 0)
    {
      if (debug_threads)
	fprintf (stderr, "  pending reinsert at %08lx", (long)process->bp_reinsert);
      if (step == 0)
	fprintf (stderr, "BAD - reinserting but not stepping.\n");
      step = 1;

      /* Postpone any pending signal.  It was enqueued above.  */
      signal = 0;
    }

  check_removed_breakpoint (process);

  if (debug_threads && the_low_target.get_pc != NULL)
    {
      fprintf (stderr, "  ");
      (long) (*the_low_target.get_pc) ();
    }

  /* If we have pending signals, consume one unless we are trying to reinsert
     a breakpoint.  */
  if (process->pending_signals != NULL && process->bp_reinsert == 0)
    {
      struct pending_signals **p_sig;

      p_sig = &process->pending_signals;
      while ((*p_sig)->prev != NULL)
	p_sig = &(*p_sig)->prev;

      signal = (*p_sig)->signal;
      free (*p_sig);
      *p_sig = NULL;
    }

  regcache_invalidate_one ((struct inferior_list_entry *)
			   get_process_thread (process));
  errno = 0;
  process->stopped = 0;
  process->stepping = step;
  ptrace (step ? PTRACE_SINGLESTEP : PTRACE_CONT, process->lwpid, 0, signal);

  current_inferior = saved_inferior;
  if (errno)
    perror_with_name ("ptrace");
}

static struct thread_resume *resume_ptr;

/* This function is called once per thread.  We look up the thread
   in RESUME_PTR, and mark the thread with a pointer to the appropriate
   resume request.

   This algorithm is O(threads * resume elements), but resume elements
   is small (and will remain small at least until GDB supports thread
   suspension).  */
static void
linux_set_resume_request (struct inferior_list_entry *entry)
{
  struct process_info *process;
  struct thread_info *thread;
  int ndx;

  thread = (struct thread_info *) entry;
  process = get_thread_process (thread);

  ndx = 0;
  while (resume_ptr[ndx].thread != -1 && resume_ptr[ndx].thread != entry->id)
    ndx++;

  process->resume = &resume_ptr[ndx];
}

/* This function is called once per thread.  We check the thread's resume
   request, which will tell us whether to resume, step, or leave the thread
   stopped; and what signal, if any, it should be sent.  For threads which
   we aren't explicitly told otherwise, we preserve the stepping flag; this
   is used for stepping over gdbserver-placed breakpoints.  */

static void
linux_continue_one_thread (struct inferior_list_entry *entry)
{
  struct process_info *process;
  struct thread_info *thread;
  int step;

  thread = (struct thread_info *) entry;
  process = get_thread_process (thread);

  if (process->resume->leave_stopped)
    return;

  if (process->resume->thread == -1)
    step = process->stepping || process->resume->step;
  else
    step = process->resume->step;

  linux_resume_one_process (&process->head, step, process->resume->sig);

  process->resume = NULL;
}

/* This function is called once per thread.  We check the thread's resume
   request, which will tell us whether to resume, step, or leave the thread
   stopped; and what signal, if any, it should be sent.  We queue any needed
   signals, since we won't actually resume.  We already have a pending event
   to report, so we don't need to preserve any step requests; they should
   be re-issued if necessary.  */

static void
linux_queue_one_thread (struct inferior_list_entry *entry)
{
  struct process_info *process;
  struct thread_info *thread;

  thread = (struct thread_info *) entry;
  process = get_thread_process (thread);

  if (process->resume->leave_stopped)
    return;

  /* If we have a new signal, enqueue the signal.  */
  if (process->resume->sig != 0)
    {
      struct pending_signals *p_sig;