2008-05-01 Daniel Jacobowitz <dan@codesourcery.com>

	    Pedro Alves  <pedro@codesourcery.com>

	Based on work by Jan Kratochvil <jan.kratochvil@redhat.com> and Jeff
 	Johnston <jjohnstn@redhat.com>.

	* NEWS: Mention attach to stopped process fix.
	* infcmd.c (detach_command, disconnect_command): Discard the thread
	list.
	* infrun.c (handle_inferior_event): Do not ignore non-SIGSTOP while
	attaching.  Use signal_stop_state.
	(signal_stop_state): Check stop_soon.
	* linux-nat.c (kill_lwp): Declare earlier.
	(pid_is_stopped, linux_nat_post_attach_wait): New.
	(lin_lwp_attach_lwp): Use linux_nat_post_attach_wait.  Update
	comments.
	(linux_nat_attach): Use linux_nat_post_attach_wait.
	(detach_callback, linux_nat_detach): Improve handling for signalled
	processes.
	(linux_nat_pid_to_str): Always print out the LWP ID if it differs
	from the process ID.
	* Makefile.in (infcmd.o): Update.

2008-05-01  Jan Kratochvil  <jan.kratochvil@redhat.com>
	    Daniel Jacobowitz  <dan@codesourcery.com>

	* gdb.threads/attach-into-signal.c, gdb.threads/attach-into-signal.exp,
	gdb.threads/attach-stopped.c, gdb.threads/attach-stopped.exp,
	gdb.threads/attachstop-mt.c, gdb.threads/attachstop-mt.exp: New.

1 files changed, 206 insertions, 76 deletions

diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
index 9511815..b09cd49 100644
--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -50,6 +50,30 @@
 #include "event-loop.h"
 #include "event-top.h"
 
+/* Note on this file's use of signals:
+
+   We stop threads by sending a SIGSTOP.  The use of SIGSTOP instead
+   of another signal is not entirely significant; we just need for a
+   signal to be delivered, so that we can intercept it.  SIGSTOP's
+   advantage is that it can not be blocked.  A disadvantage is that it
+   is not a real-time signal, so it can only be queued once; we do not
+   keep track of other sources of SIGSTOP.
+
+   Two other signals that can't be blocked are SIGCONT and SIGKILL.
+   But we can't use them, because they have special behavior when the
+   signal is generated - not when it is delivered.  SIGCONT resumes
+   the entire thread group and SIGKILL kills the entire thread group.
+
+   A delivered SIGSTOP would stop the entire thread group, not just the
+   thread we tkill'd.  But we never let the SIGSTOP deliver; we always
+   intercept and cancel it (by PTRACE_CONT without passing SIGSTOP).
+
+   We could use a real-time signal instead.  This would solve those
+   problems; we could use PTRACE_GETSIGINFO to locate the specific
+   stop signals sent by GDB.  But we would still have to have some
+   support for SIGSTOP, since PTRACE_ATTACH generates it, and there
+   are races with trying to find a signal that is not blocked.  */
+
 #ifndef O_LARGEFILE
 #define O_LARGEFILE 0
 #endif
@@ -186,6 +210,7 @@ static void linux_nat_async (void (*callback)
 			     (enum inferior_event_type event_type, void *context),
 			     void *context);
 static int linux_nat_async_mask (int mask);
+static int kill_lwp (int lwpid, int signo);
 
 /* Captures the result of a successful waitpid call, along with the
    options used in that call.  */
@@ -1010,10 +1035,103 @@ exit_lwp (struct lwp_info *lp)
   delete_lwp (lp->ptid);
 }
 
-/* Attach to the LWP specified by PID.  If VERBOSE is non-zero, print
-   a message telling the user that a new LWP has been added to the
-   process.  Return 0 if successful or -1 if the new LWP could not
-   be attached.  */
+/* Detect `T (stopped)' in `/proc/PID/status'.
+   Other states including `T (tracing stop)' are reported as false.  */
+
+static int
+pid_is_stopped (pid_t pid)
+{
+  FILE *status_file;
+  char buf[100];
+  int retval = 0;
+
+  snprintf (buf, sizeof (buf), "/proc/%d/status", (int) pid);
+  status_file = fopen (buf, "r");
+  if (status_file != NULL)
+    {
+      int have_state = 0;
+
+      while (fgets (buf, sizeof (buf), status_file))
+	{
+	  if (strncmp (buf, "State:", 6) == 0)
+	    {
+	      have_state = 1;
+	      break;
+	    }
+	}
+      if (have_state && strstr (buf, "T (stopped)") != NULL)
+	retval = 1;
+      fclose (status_file);
+    }
+  return retval;
+}
+
+/* Wait for the LWP specified by LP, which we have just attached to.
+   Returns a wait status for that LWP, to cache.  */
+
+static int
+linux_nat_post_attach_wait (ptid_t ptid, int first, int *cloned,
+			    int *signalled)
+{
+  pid_t new_pid, pid = GET_LWP (ptid);
+  int status;
+
+  if (pid_is_stopped (pid))
+    {
+      if (debug_linux_nat)
+	fprintf_unfiltered (gdb_stdlog,
+			    "LNPAW: Attaching to a stopped process\n");
+
+      /* The process is definitely stopped.  It is in a job control
+	 stop, unless the kernel predates the TASK_STOPPED /
+	 TASK_TRACED distinction, in which case it might be in a
+	 ptrace stop.  Make sure it is in a ptrace stop; from there we
+	 can kill it, signal it, et cetera.
+
+         First make sure there is a pending SIGSTOP.  Since we are
+	 already attached, the process can not transition from stopped
+	 to running without a PTRACE_CONT; so we know this signal will
+	 go into the queue.  The SIGSTOP generated by PTRACE_ATTACH is
+	 probably already in the queue (unless this kernel is old
+	 enough to use TASK_STOPPED for ptrace stops); but since SIGSTOP
+	 is not an RT signal, it can only be queued once.  */
+      kill_lwp (pid, SIGSTOP);
+
+      /* Finally, resume the stopped process.  This will deliver the SIGSTOP
+	 (or a higher priority signal, just like normal PTRACE_ATTACH).  */
+      ptrace (PTRACE_CONT, pid, 0, 0);
+    }
+
+  /* Make sure the initial process is stopped.  The user-level threads
+     layer might want to poke around in the inferior, and that won't
+     work if things haven't stabilized yet.  */
+  new_pid = my_waitpid (pid, &status, 0);
+  if (new_pid == -1 && errno == ECHILD)
+    {
+      if (first)
+	warning (_("%s is a cloned process"), target_pid_to_str (ptid));
+
+      /* Try again with __WCLONE to check cloned processes.  */
+      new_pid = my_waitpid (pid, &status, __WCLONE);
+      *cloned = 1;
+    }
+
+  gdb_assert (pid == new_pid && WIFSTOPPED (status));
+
+  if (WSTOPSIG (status) != SIGSTOP)
+    {
+      *signalled = 1;
+      if (debug_linux_nat)
+	fprintf_unfiltered (gdb_stdlog,
+			    "LNPAW: Received %s after attaching\n",
+			    status_to_str (status));
+    }
+
+  return status;
+}
+
+/* Attach to the LWP specified by PID.  Return 0 if successful or -1
+   if the new LWP could not be attached.  */
 
 int
 lin_lwp_attach_lwp (ptid_t ptid)
@@ -1036,9 +1154,7 @@ lin_lwp_attach_lwp (ptid_t ptid)
      to happen.  */
   if (GET_LWP (ptid) != GET_PID (ptid) && lp == NULL)
     {
-      pid_t pid;
-      int status;
-      int cloned = 0;
+      int status, cloned = 0, signalled = 0;
 
       if (ptrace (PTRACE_ATTACH, GET_LWP (ptid), 0, 0) < 0)
 	{
@@ -1057,24 +1173,18 @@ lin_lwp_attach_lwp (ptid_t ptid)
 			    "LLAL: PTRACE_ATTACH %s, 0, 0 (OK)\n",
 			    target_pid_to_str (ptid));
 
-      pid = my_waitpid (GET_LWP (ptid), &status, 0);
-      if (pid == -1 && errno == ECHILD)
+      status = linux_nat_post_attach_wait (ptid, 0, &cloned, &signalled);
+      lp = add_lwp (ptid);
+      lp->stopped = 1;
+      lp->cloned = cloned;
+      lp->signalled = signalled;
+      if (WSTOPSIG (status) != SIGSTOP)
 	{
-	  /* Try again with __WCLONE to check cloned processes.  */
-	  pid = my_waitpid (GET_LWP (ptid), &status, __WCLONE);
-	  cloned = 1;
+	  lp->resumed = 1;
+	  lp->status = status;
 	}
 
-      gdb_assert (pid == GET_LWP (ptid)
-		  && WIFSTOPPED (status) && WSTOPSIG (status));
-
-      if (lp == NULL)
-	lp = add_lwp (ptid);
-      lp->cloned = cloned;
-
-      target_post_attach (pid);
-
-      lp->stopped = 1;
+      target_post_attach (GET_LWP (lp->ptid));
 
       if (debug_linux_nat)
 	{
@@ -1133,10 +1243,7 @@ static void
 linux_nat_attach (char *args, int from_tty)
 {
   struct lwp_info *lp;
-  pid_t pid;
   int status;
-  int cloned = 0;
-  int options = 0;
 
   /* FIXME: We should probably accept a list of process id's, and
      attach all of them.  */
@@ -1151,54 +1258,69 @@ linux_nat_attach (char *args, int from_tty)
       sigdelset (&suspend_mask, SIGCHLD);
     }
 
-  /* Make sure the initial process is stopped.  The user-level threads
-     layer might want to poke around in the inferior, and that won't
-     work if things haven't stabilized yet.  */
-  pid = my_waitpid (GET_PID (inferior_ptid), &status, options);
-  if (pid == -1 && errno == ECHILD)
-    {
-      warning (_("%s is a cloned process"), target_pid_to_str (inferior_ptid));
-
-      /* Try again with __WCLONE to check cloned processes.  */
-      options = __WCLONE;
-      pid = my_waitpid (GET_PID (inferior_ptid), &status, options);
-      cloned = 1;
-    }
-
-  gdb_assert (pid == GET_PID (inferior_ptid)
-	      && WIFSTOPPED (status) && WSTOPSIG (status) == SIGSTOP);
-
   /* Add the initial process as the first LWP to the list.  */
   inferior_ptid = BUILD_LWP (GET_PID (inferior_ptid), GET_PID (inferior_ptid));
   lp = add_lwp (inferior_ptid);
-  lp->cloned = cloned;
+
+  status = linux_nat_post_attach_wait (lp->ptid, 1, &lp->cloned,
+				       &lp->signalled);
+  lp->stopped = 1;
 
   /* If this process is not using thread_db, then we still don't
      detect any other threads, but add at least this one.  */
   add_thread_silent (lp->ptid);
 
-  lp->stopped = 1;
+  /* Save the wait status to report later.  */
   lp->resumed = 1;
+  if (debug_linux_nat)
+    fprintf_unfiltered (gdb_stdlog,
+			"LNA: waitpid %ld, saving status %s\n",
+			(long) GET_PID (lp->ptid), status_to_str (status));
 
   if (!target_can_async_p ())
-    {
-      /* Fake the SIGSTOP that core GDB expects.  */
-      lp->status = W_STOPCODE (SIGSTOP);
-      if (debug_linux_nat)
-	fprintf_unfiltered (gdb_stdlog,
-			    "LNA: waitpid %ld, faking SIGSTOP\n", (long) pid);
-    }
+    lp->status = status;
   else
     {
       /* We already waited for this LWP, so put the wait result on the
 	 pipe.  The event loop will wake up and gets us to handling
 	 this event.  */
-      linux_nat_event_pipe_push (pid, status, options);
+      linux_nat_event_pipe_push (GET_PID (lp->ptid), status,
+				 lp->cloned ? __WCLONE : 0);
       /* Register in the event loop.  */
       target_async (inferior_event_handler, 0);
     }
 }
 
+/* Get pending status of LP.  */
+static int
+get_pending_status (struct lwp_info *lp, int *status)
+{
+  struct target_waitstatus last;
+  ptid_t last_ptid;
+
+  get_last_target_status (&last_ptid, &last);
+
+  /* If this lwp is the ptid that GDB is processing an event from, the
+     signal will be in stop_signal.  Otherwise, in all-stop + sync
+     mode, we may cache pending events in lp->status while trying to
+     stop all threads (see stop_wait_callback).  In async mode, the
+     events are always cached in waitpid_queue.  */
+
+  *status = 0;
+  if (GET_LWP (lp->ptid) == GET_LWP (last_ptid))
+    {
+      if (stop_signal != TARGET_SIGNAL_0
+	  && signal_pass_state (stop_signal))
+	*status = W_STOPCODE (target_signal_to_host (stop_signal));
+    }
+  else if (target_can_async_p ())
+    queued_waitpid (GET_LWP (lp->ptid), status, __WALL);
+  else
+    *status = lp->status;
+
+  return 0;
+}
+
 static int
 detach_callback (struct lwp_info *lp, void *data)
 {
@@ -1209,40 +1331,30 @@ detach_callback (struct lwp_info *lp, void *data)
 			strsignal (WSTOPSIG (lp->status)),
 			target_pid_to_str (lp->ptid));
 
-  while (lp->signalled && lp->stopped)
+  /* If there is a pending SIGSTOP, get rid of it.  */
+  if (lp->signalled)
     {
-      errno = 0;
-      if (ptrace (PTRACE_CONT, GET_LWP (lp->ptid), 0,
-		  WSTOPSIG (lp->status)) < 0)
-	error (_("Can't continue %s: %s"), target_pid_to_str (lp->ptid),
-	       safe_strerror (errno));
-
       if (debug_linux_nat)
 	fprintf_unfiltered (gdb_stdlog,
-			    "DC:  PTRACE_CONTINUE (%s, 0, %s) (OK)\n",
-			    target_pid_to_str (lp->ptid),
-			    status_to_str (lp->status));
+			    "DC: Sending SIGCONT to %s\n",
+			    target_pid_to_str (lp->ptid));
 
-      lp->stopped = 0;
+      kill_lwp (GET_LWP (lp->ptid), SIGCONT);
       lp->signalled = 0;
-      lp->status = 0;
-      /* FIXME drow/2003-08-26: There was a call to stop_wait_callback
-	 here.  But since lp->signalled was cleared above,
-	 stop_wait_callback didn't do anything; the process was left
-	 running.  Shouldn't we be waiting for it to stop?
-	 I've removed the call, since stop_wait_callback now does do
-	 something when called with lp->signalled == 0.  */
-
-      gdb_assert (lp->status == 0 || WIFSTOPPED (lp->status));
     }
 
   /* We don't actually detach from the LWP that has an id equal to the
      overall process id just yet.  */
   if (GET_LWP (lp->ptid) != GET_PID (lp->ptid))
     {
+      int status = 0;
+
+      /* Pass on any pending signal for this LWP.  */
+      get_pending_status (lp, &status);
+
       errno = 0;
       if (ptrace (PTRACE_DETACH, GET_LWP (lp->ptid), 0,
-		  WSTOPSIG (lp->status)) < 0)
+		  WSTOPSIG (status)) < 0)
 	error (_("Can't detach %s: %s"), target_pid_to_str (lp->ptid),
 	       safe_strerror (errno));
 
@@ -1252,7 +1364,6 @@ detach_callback (struct lwp_info *lp, void *data)
 			    target_pid_to_str (lp->ptid),
 			    strsignal (WSTOPSIG (lp->status)));
 
-      drain_queued_events (GET_LWP (lp->ptid));
       delete_lwp (lp->ptid);
     }
 
@@ -1263,6 +1374,9 @@ static void
 linux_nat_detach (char *args, int from_tty)
 {
   int pid;
+  int status;
+  enum target_signal sig;
+
   if (target_can_async_p ())
     linux_nat_async (NULL, 0);
 
@@ -1271,6 +1385,21 @@ linux_nat_detach (char *args, int from_tty)
   /* Only the initial process should be left right now.  */
   gdb_assert (num_lwps == 1);
 
+  /* Pass on any pending signal for the last LWP.  */
+  if ((args == NULL || *args == '\0')
+      && get_pending_status (lwp_list, &status) != -1
+      && WIFSTOPPED (status))
+    {
+      /* Put the signal number in ARGS so that inf_ptrace_detach will
+	 pass it along with PTRACE_DETACH.  */
+      args = alloca (8);
+      sprintf (args, "%d", (int) WSTOPSIG (status));
+      fprintf_unfiltered (gdb_stdlog,
+			  "LND: Sending signal %s to %s\n",
+			  args,
+			  target_pid_to_str (lwp_list->ptid));
+    }
+
   trap_ptid = null_ptid;
 
   /* Destroy LWP info; it's no longer valid.  */
@@ -2848,7 +2977,9 @@ linux_nat_pid_to_str (ptid_t ptid)
 {
   static char buf[64];
 
-  if (lwp_list && lwp_list->next && is_lwp (ptid))
+  if (is_lwp (ptid)
+      && ((lwp_list && lwp_list->next)
+	  || GET_PID (ptid) != GET_LWP (ptid)))
     {
       snprintf (buf, sizeof (buf), "LWP %ld", GET_LWP (ptid));
       return buf;
@@ -4205,4 +4336,3 @@ lin_thread_get_thread_signals (sigset_t *set)
   /* ... except during a sigsuspend.  */
   sigdelset (&suspend_mask, cancel);
 }
-