Per-inferior target_terminal state, fix PR gdb/13211, more

In my multi-target branch I ran into problems with GDB's terminal
handling that exist in master as well, with multi-inferior debugging.

This patch adds a testcase for said problems
(gdb.multi/multi-term-settings.exp), fixes the problems, fixes PR
gdb/13211 as well (and adds a testcase for that too,
gdb.base/interrupt-daemon.exp).

The basis of the problem I ran into is the following.  Consider a
scenario where you have:

 - inferior 1 - started with "attach", process is running on some
   other terminal.

 - inferior 2 - started with "run", process is sharing gdb's terminal.

In this scenario, when you stop/resume both inferiors, you want GDB to
save/restore the terminal settings of inferior 2, the one that is
sharing GDB's terminal.  I.e., you want inferior 2 to "own" the
terminal (in target_terminal::is_ours/target_terminal::is_inferior
sense).

Unfortunately, that's not what you get currently.  Because GDB doesn't
know whether an attached inferior is actually sharing GDB's terminal,
it tries to save/restore its settings anyway, ignoring errors.  In
this case, this is pointless, because inferior 1 is running on a
different terminal, but GDB doesn't know better.

And then, because it is only possible to have the terminal settings of
a single inferior be in effect at a time, or make one inferior/pgrp be
the terminal's foreground pgrp (aka, only one inferior can "own" the
terminal, ignoring fork children here), if GDB happens to try to
restore the terminal settings of inferior 1 first, then GDB never
restores the terminal settings of inferior 2.

This patch fixes that and a few things more along the way:

 - Moves enum target_terminal::terminal_state out of the
   target_terminal class (it's currently private) and makes it a
   scoped enum so that it can be easily used elsewhere.

 - Replaces the inflow.c:terminal_is_ours boolean with a
   target_terminal_state variable.  This allows distinguishing is_ours
   and is_ours_for_output states.  This allows finally making
   child_terminal_ours_1 do something with its "output_only"
   parameter.

 - Makes each inferior have its own copy of the
   is_ours/is_ours_for_output/is_inferior state.

 - Adds a way for GDB to tell whether the inferior is sharing GDB's
   terminal.  Works best on Linux and Solaris; the fallback works just
   as well as currently.

 - With that, we can remove the inf->attach_flag tests from
   child_terminal_inferior/child_terminal_ours.

 - Currently target_ops.to_ours is responsible for both saving the
   current inferior's terminal state, and restoring gdb's state.
   Because each inferior has its own terminal state (possibly handled
   by different targets in a multi-target world, even), we need to
   split the inferior-saving part from the gdb-restoring part.  The
   patch adds a new target_ops.to_save_inferior target method for
   that.

 - Adds a new target_terminal::save_inferior() function, so that
   sequences like:

     scoped_restore_terminal_state save_state;
     target_terminal::ours_for_output ();

   ... restore back inferiors that were
   target_terminal_state::is_inferior before back to is_inferior, and
   leaves inferiors that were is_ours alone.

 - Along the way, this adds a default implementation of
   target_pass_ctrlc to inflow.c (for inf-child.c), that handles
   passing the Ctrl-C to a process running on GDB's terminal or to
   some other process otherwise.

 - Similarly, adds a new target default implementation of
   target_interrupt, for the "interrupt" command.  The current
   implementation of this hook in inf-ptrace.c kills the whole process
   group, but that's incorrect/undesirable because we may not be
   attached to all processes in the process group.  And also, it's
   incorrect because inferior_process_group() doesn't really return
   the inferior's real process group id if the inferior is not a
   process group leader...  This is the cause of PR gdb/13211 [1],
   which this patch fixes.  While at it, that target method's "ptid"
   parameter is eliminated, because it's not really used.

 - A new test is included that exercises and fixes PR gdb/13211, and
   also fixes a GDB issue reported on stackoverflow that I ran into
   while working on this [2].  The problem is similar to PR gdb/13211,
   except that it also triggers with Ctrl-C.  When debugging a daemon
   (i.e., a process that disconnects from the controlling terminal and
   is not a process group leader, then Ctrl-C doesn't work, you just
   can't interrupt the inferior at all, resulting in a hung debug
   session.  The problem is that since the inferior is no longer
   associated with gdb's session / controlling terminal, then trying
   to put the inferior in the foreground fails.  And so Ctrl-C never
   reaches the inferior directly.  pass_signal is only used when the
   inferior is attached, but that is not the case here.  This is fixed
   by the new child_pass_ctrlc.  Without the fix, the new
   interrupt-daemon.exp testcase fails with timeout waiting for a
   SIGINT that never arrives.

[1] PR gdb/13211 - Async / Process group and interrupt not working
https://sourceware.org/bugzilla/show_bug.cgi?id=13211

[2] GDB not reacting Ctrl-C when after fork() and setsid()
https://stackoverflow.com/questions/46101292/gdb-not-reacting-ctrl-c-when-after-fork-and-setsid

Note this patch does _not_ fix:

 - PR gdb/14559 - The 'interrupt' command does not work if sigwait is in use
   https://sourceware.org/bugzilla/show_bug.cgi?id=14559

 - PR gdb/9425 - When using "sigwait" GDB doesn't trap SIGINT. Ctrl+C terminates program when should break gdb.
   https://sourceware.org/bugzilla/show_bug.cgi?id=9425

The only way to fix that that I know of (without changing the kernel)
is to make GDB put inferiors in a separate session (create a
pseudo-tty master/slave pair, make the inferior run with the slave as
its terminal, and have gdb pump output/input on the master end).

gdb/ChangeLog:
2018-01-30  Pedro Alves  <palves@redhat.com>

	PR gdb/13211
	* config.in, configure: Regenerate.
	* configure.ac: Check for getpgid.
	* go32-nat.c (go32_pass_ctrlc): New.
	(go32_target): Install it.
	* inf-child.c (inf_child_target): Install
	child_terminal_save_inferior, child_pass_ctrlc and
	child_interrupt.
	* inf-ptrace.c (inf_ptrace_interrupt): Delete.
	(inf_ptrace_target): No longer install it.
	* infcmd.c (interrupt_target_1): Adjust.
	* inferior.h (child_terminal_save_inferior, child_pass_ctrlc)
	(child_interrupt): Declare.
	(inferior::terminal_state): New.
	* inflow.c (struct terminal_info): Update comments.
	(inferior_process_group): Delete.
	(terminal_is_ours): Delete.
	(gdb_tty_state): New.
	(child_terminal_init): Adjust.
	(is_gdb_terminal, sharing_input_terminal_1)
	(sharing_input_terminal): New functions.
	(child_terminal_inferior): Adjust.  Use sharing_input_terminal.
	Set the process's actual process group in the foreground if
	possible.  Handle is_ours_for_output/is_ours distinction.  Don't
	mark terminal as the inferior's if not sharing GDB's terminal.
	Don't check attach_flag.
	(child_terminal_ours_for_output, child_terminal_ours): Adjust to
	pass down a target_terminal_state.
	(child_terminal_save_inferior): New, factored out from ...
	(child_terminal_ours_1): ... this.  Handle
	target_terminal_state::is_ours_for_output.
	(child_interrupt, child_pass_ctrlc): New.
	(inflow_inferior_exit): Clear the inferior's terminal_state.
	(copy_terminal_info): Copy the inferior's terminal state.
	(_initialize_inflow): Remove reference to terminal_is_ours.
	* inflow.h (inferior_process_group): Delete.
	* nto-procfs.c (nto_handle_sigint, procfs_interrupt): Adjust.
	* procfs.c (procfs_target): Don't install procfs_interrupt.
	(procfs_interrupt): Delete.
	* remote.c (remote_serial_quit_handler): Adjust.
	(remote_interrupt): Remove ptid parameter.  Adjust.
	* target-delegates.c: Regenerate.
	* target.c: Include "terminal.h".
	(target_terminal::terminal_state): Rename to ...
	(target_terminal::m_terminal_state): ... this.
	(target_terminal::init): Adjust.
	(target_terminal::inferior): Adjust to per-inferior
	terminal_state.
	(target_terminal::restore_inferior, target_terminal_is_ours_kind): New.
	(target_terminal::ours, target_terminal::ours_for_output): Use
	target_terminal_is_ours_kind.
	(target_interrupt): Remove ptid parameter.  Adjust.
	(default_target_pass_ctrlc): Adjust.
	* target.h (target_ops::to_terminal_save_inferior): New field.
	(target_ops::to_interrupt): Remove ptid_t parameter.
	(target_interrupt): Remove ptid_t parameter.  Update comment.
	(target_pass_ctrlc): Update comment.
	* target/target.h (target_terminal_state): New scoped enum,
	factored out of ...
	(target_terminal::terminal_state): ... here.
	(target_terminal::inferior): Update comments.
	(target_terminal::restore_inferior): New.
	(target_terminal::is_inferior, target_terminal::is_ours)
	(target_terminal::is_ours_for_output): Adjust.
	(target_terminal::scoped_restore_terminal_state): Adjust to
	rename, and call restore_inferior() instead of inferior().
	(target_terminal::scoped_restore_terminal_state::m_state): Change
	type.
	(target_terminal::terminal_state): Rename to ...
	(target_terminal::m_terminal_state): ... this and change type.

gdb/gdbserver/ChangeLog:
2018-01-30  Pedro Alves  <palves@redhat.com>

	PR gdb/13211
	* target.c (target_terminal::terminal_state): Rename to ...
	(target_terminal::m_terminal_state): ... this.

gdb/testsuite/ChangeLog:
2018-01-30  Pedro Alves  <palves@redhat.com>

	PR gdb/13211
	* gdb.base/interrupt-daemon.c: New.
	* gdb.base/interrupt-daemon.exp: New.
	* gdb.multi/multi-term-settings.c: New.
	* gdb.multi/multi-term-settings.exp: New.

1 files changed, 308 insertions, 100 deletions

diff --git a/gdb/inflow.c b/gdb/inflow.c
index 6984e8f4557..7c5e9047030 100644
--- a/gdb/inflow.c
+++ b/gdb/inflow.c
@@ -46,7 +46,7 @@
 
 static void pass_signal (int);
 
-static void child_terminal_ours_1 (int);
+static void child_terminal_ours_1 (target_terminal_state);
 
 /* Record terminal status separately for debugger and inferior.  */
 
@@ -54,8 +54,8 @@ static struct serial *stdin_serial;
 
 /* Terminal related info we need to keep track of.  Each inferior
    holds an instance of this structure --- we save it whenever the
-   corresponding inferior stops, and restore it to the foreground
-   inferior when it resumes.  */
+   corresponding inferior stops, and restore it to the terminal when
+   the inferior is resumed in the foreground.  */
 struct terminal_info
 {
   /* The name of the tty (from the `tty' command) that we gave to the
@@ -63,11 +63,23 @@ struct terminal_info
   char *run_terminal;
 
   /* TTY state.  We save it whenever the inferior stops, and restore
-     it when it resumes.  */
+     it when it resumes in the foreground.  */
   serial_ttystate ttystate;
 
 #ifdef HAVE_TERMIOS_H
-  /* Process group.  Saved and restored just like ttystate.  */
+  /* The terminal's foreground process group.  Saved whenever the
+     inferior stops.  This is the pgrp displayed by "info terminal".
+     Note that this may be not the inferior's actual process group,
+     since each inferior that we spawn has its own process group, and
+     only one can be in the foreground at a time.  When the inferior
+     resumes, if we can determine the inferior's actual pgrp, then we
+     make that the foreground pgrp instead of what was saved here.
+     While it's a bit arbitrary which inferior's pgrp ends up in the
+     foreground when we resume several inferiors, this at least makes
+     'resume inf1+inf2' + 'stop all' + 'resume inf2' end up with
+     inf2's pgrp in the foreground instead of inf1's (which would be
+     problematic since it would be left stopped: Ctrl-C wouldn't work,
+     for example).  */
   pid_t process_group;
 #endif
 
@@ -120,17 +132,6 @@ private:
 #endif
 };
 
-#ifdef HAVE_TERMIOS_H
-
-/* Return the process group of the current inferior.  */
-
-pid_t
-inferior_process_group (void)
-{
-  return get_inflow_inferior_data (current_inferior ())->process_group;
-}
-#endif
-
 /* While the inferior is running, we want SIGINT and SIGQUIT to go to the
    inferior only.  If we have job control, that takes care of it.  If not,
    we save our handlers in these two variables and set SIGINT and SIGQUIT
@@ -146,11 +147,17 @@ static sighandler_t sigquit_ours;
    fork_inferior, while forking a new child.  */
 static const char *inferior_thisrun_terminal;
 
-/* Nonzero if our terminal settings are in effect.  Zero if the
-   inferior's settings are in effect.  Ignored if !gdb_has_a_terminal
-   ().  */
+/* Track who owns GDB's terminal (is it GDB or some inferior?).  While
+   target_terminal::is_ours() etc. tracks the core's intention and is
+   independent of the target backend, this tracks the actual state of
+   GDB's own tty.  So for example,
+
+     (target_terminal::is_inferior () && gdb_tty_state == terminal_is_ours)
 
-int terminal_is_ours;
+   is true when the (native) inferior is not sharing a terminal with
+   GDB (e.g., because we attached to an inferior that is running on a
+   different terminal).  */
+static target_terminal_state gdb_tty_state = target_terminal_state::is_ours;
 
 /* See terminal.h.  */
 
@@ -196,29 +203,21 @@ gdb_has_a_terminal (void)
 void
 child_terminal_init (struct target_ops *self)
 {
-  struct inferior *inf = current_inferior ();
-  struct terminal_info *tinfo = get_inflow_inferior_data (inf);
+  if (!gdb_has_a_terminal ())
+    return;
+
+  inferior *inf = current_inferior ();
+  terminal_info *tinfo = get_inflow_inferior_data (inf);
 
 #ifdef HAVE_TERMIOS_H
-  /* Store the process group even without a terminal as it is used not
-     only to reset the tty foreground process group, but also to
-     interrupt the inferior.  A child we spawn should be a process
-     group leader (PGID==PID) at this point, though that may not be
-     true if we're attaching to an existing process.  */
+  /* A child we spawn should be a process group leader (PGID==PID) at
+     this point, though that may not be true if we're attaching to an
+     existing process.  */
   tinfo->process_group = inf->pid;
 #endif
 
-  if (gdb_has_a_terminal ())
-    {
-      xfree (tinfo->ttystate);
-      tinfo->ttystate = serial_copy_tty_state (stdin_serial,
-					       initial_gdb_ttystate);
-
-      /* Make sure that next time we call terminal_inferior (which will be
-         before the program runs, as it needs to be), we install the new
-         process group.  */
-      terminal_is_ours = 1;
-    }
+  xfree (tinfo->ttystate);
+  tinfo->ttystate = serial_copy_tty_state (stdin_serial, initial_gdb_ttystate);
 }
 
 /* Save the terminal settings again.  This is necessary for the TUI
@@ -235,31 +234,137 @@ gdb_save_tty_state (void)
     }
 }
 
-/* Put the inferior's terminal settings into effect.
-   This is preparation for starting or resuming the inferior.
+/* Try to determine whether TTY is GDB's input terminal.  Returns
+   TRIBOOL_UNKNOWN if we can't tell.  */
 
-   N.B. Targets that want to use this with async support must build that
-   support on top of this (e.g., the caller still needs to remove stdin
-   from the event loop).  E.g., see linux_nat_terminal_inferior.  */
+static tribool
+is_gdb_terminal (const char *tty)
+{
+  struct stat gdb_tty;
+  struct stat other_tty;
+  int res;
+
+  res = stat (tty, &other_tty);
+  if (res == -1)
+    return TRIBOOL_UNKNOWN;
+
+  res = fstat (STDIN_FILENO, &gdb_tty);
+  if (res == -1)
+    return TRIBOOL_UNKNOWN;
+
+  return ((gdb_tty.st_dev == other_tty.st_dev
+	   && gdb_tty.st_ino == other_tty.st_ino)
+	  ? TRIBOOL_TRUE
+	  : TRIBOOL_FALSE);
+}
+
+/* Helper for sharing_input_terminal.  Try to determine whether
+   inferior INF is using the same TTY for input as GDB is.  Returns
+   TRIBOOL_UNKNOWN if we can't tell.  */
+
+static tribool
+sharing_input_terminal_1 (inferior *inf)
+{
+  /* Using host-dependent code here is fine, because the
+     child_terminal_foo functions are meant to be used by child/native
+     targets.  */
+#if defined (__linux__) || defined (__sun__)
+  char buf[100];
+
+  xsnprintf (buf, sizeof (buf), "/proc/%d/fd/0", inf->pid);
+  return is_gdb_terminal (buf);
+#else
+  return TRIBOOL_UNKNOWN;
+#endif
+}
+
+/* Return true if the inferior is using the same TTY for input as GDB
+   is.  If this is true, then we save/restore terminal flags/state.
+
+   This is necessary because if inf->attach_flag is set, we don't
+   offhand know whether we are sharing a terminal with the inferior or
+   not.  Attaching a process without a terminal is one case where we
+   do not; attaching a process which we ran from the same shell as GDB
+   via `&' is one case where we do.
+
+   If we can't determine, we assume the TTY is being shared.  This
+   works OK if you're only debugging one inferior.  However, if you're
+   debugging more than one inferior, and e.g., one is spawned by GDB
+   with "run" (sharing terminal with GDB), and another is attached to
+   (and running on a different terminal, as is most common), then it
+   matters, because we can only restore the terminal settings of one
+   of the inferiors, and in that scenario, we want to restore the
+   settings of the "run"'ed inferior.
+
+   Note, this is not the same as determining whether GDB and the
+   inferior are in the same session / connected to the same
+   controlling tty.  An inferior (fork child) may call setsid,
+   disconnecting itself from the ctty, while still leaving
+   stdin/stdout/stderr associated with the original terminal.  If
+   we're debugging that process, we should also save/restore terminal
+   settings.  */
+
+static bool
+sharing_input_terminal (inferior *inf)
+{
+  terminal_info *tinfo = get_inflow_inferior_data (inf);
+
+  tribool res = sharing_input_terminal_1 (inf);
+
+  if (res == TRIBOOL_UNKNOWN)
+    {
+      /* As fallback, if we can't determine by stat'ing the inferior's
+	 tty directly (because it's not supported on this host) and
+	 the child was spawned, check whether run_terminal is our tty.
+	 This isn't ideal, since this is checking the child's
+	 controlling terminal, not the input terminal (which may have
+	 been redirected), but is still better than nothing.  A false
+	 positive ("set inferior-tty" points to our terminal, but I/O
+	 was redirected) is much more likely than a false negative
+	 ("set inferior-tty" points to some other terminal, and then
+	 output was redirected to our terminal), and with a false
+	 positive we just end up trying to save/restore terminal
+	 settings when we didn't need to or we actually can't.  */
+      if (tinfo->run_terminal != NULL)
+	res = is_gdb_terminal (tinfo->run_terminal);
+
+      /* If we still can't determine, assume yes.  */
+      if (res == TRIBOOL_UNKNOWN)
+	return true;
+    }
+
+  return res == TRIBOOL_TRUE;
+}
+
+/* Put the inferior's terminal settings into effect.  This is
+   preparation for starting or resuming the inferior.  */
 
 void
 child_terminal_inferior (struct target_ops *self)
 {
-  struct inferior *inf;
-  struct terminal_info *tinfo;
-
-  if (!terminal_is_ours)
+  /* If we resume more than one inferior in the foreground on GDB's
+     terminal, then the first inferior's terminal settings "win".
+     Note that every child process is put in its own process group, so
+     the first process that ends up resumed ends up determining which
+     process group the kernel forwards Ctrl-C/Ctrl-Z (SIGINT/SIGTTOU)
+     to.  */
+  if (gdb_tty_state == target_terminal_state::is_inferior)
     return;
 
-  inf = current_inferior ();
-  tinfo = get_inflow_inferior_data (inf);
+  inferior *inf = current_inferior ();
+  terminal_info *tinfo = get_inflow_inferior_data (inf);
 
   if (gdb_has_a_terminal ()
       && tinfo->ttystate != NULL
-      && tinfo->run_terminal == NULL)
+      && sharing_input_terminal (inf))
     {
       int result;
 
+      /* Ignore SIGTTOU since it will happen when we try to set the
+	 terminal's state (if gdb_tty_state is currently
+	 ours_for_output).  */
+      scoped_ignore_sigttou ignore_sigttou;
+
 #ifdef F_GETFL
       result = fcntl (0, F_SETFL, tinfo->tflags);
       OOPSY ("fcntl F_SETFL");
@@ -276,28 +381,40 @@ child_terminal_inferior (struct target_ops *self)
 #endif
 	}
 
-      /* If attach_flag is set, we don't know whether we are sharing a
-         terminal with the inferior or not.  (attaching a process
-         without a terminal is one case where we do not; attaching a
-         process which we ran from the same shell as GDB via `&' is
-         one case where we do, I think (but perhaps this is not
-         `sharing' in the sense that we need to save and restore tty
-         state)).  I don't know if there is any way to tell whether we
-         are sharing a terminal.  So what we do is to go through all
-         the saving and restoring of the tty state, but ignore errors
-         setting the process group, which will happen if we are not
-         sharing a terminal).  */
-
       if (job_control)
 	{
 #ifdef HAVE_TERMIOS_H
+	  /* If we can't tell the inferior's actual process group,
+	     then restore whatever was the foreground pgrp the last
+	     time the inferior was running.  See also comments
+	     describing terminal_state::process_group.  */
+#ifdef HAVE_GETPGID
+	  result = tcsetpgrp (0, getpgid (inf->pid));
+#else
 	  result = tcsetpgrp (0, tinfo->process_group);
-	  if (!inf->attach_flag)
-	    OOPSY ("tcsetpgrp");
+#endif
+	  if (result == -1)
+	    {
+#if 0
+	      /* This fails if either GDB has no controlling terminal,
+		 e.g., running under 'setsid(1)', or if the inferior
+		 is not attached to GDB's controlling terminal.  E.g.,
+		 if it called setsid to create a new session or used
+		 the TIOCNOTTY ioctl, or simply if we've attached to a
+		 process running on another terminal and we couldn't
+		 tell whether it was sharing GDB's terminal (and so
+		 assumed yes).  */
+	      fprintf_unfiltered
+		(gdb_stderr,
+		 "[tcsetpgrp failed in child_terminal_inferior: %s]\n",
+		 safe_strerror (errno));
+#endif
+	    }
 #endif
 	}
+
+      gdb_tty_state = target_terminal_state::is_inferior;
     }
-  terminal_is_ours = 0;
 }
 
 /* Put some of our terminal settings into effect,
@@ -314,7 +431,7 @@ child_terminal_inferior (struct target_ops *self)
 void
 child_terminal_ours_for_output (struct target_ops *self)
 {
-  child_terminal_ours_1 (1);
+  child_terminal_ours_1 (target_terminal_state::is_ours_for_output);
 }
 
 /* Put our terminal settings into effect.
@@ -328,35 +445,50 @@ child_terminal_ours_for_output (struct target_ops *self)
 void
 child_terminal_ours (struct target_ops *self)
 {
-  child_terminal_ours_1 (0);
+  child_terminal_ours_1 (target_terminal_state::is_ours);
 }
 
-/* output_only is not used, and should not be used unless we introduce
-   separate terminal_is_ours and terminal_is_ours_for_output
-   flags.  */
+/* Save the current terminal settings in the inferior's terminal_info
+   cache.  */
 
-static void
-child_terminal_ours_1 (int output_only)
+void
+child_terminal_save_inferior (struct target_ops *self)
 {
-  struct inferior *inf;
-  struct terminal_info *tinfo;
+  /* Avoid attempting all the ioctl's when running in batch.  */
+  if (!gdb_has_a_terminal ())
+    return;
 
-  if (terminal_is_ours)
+  inferior *inf = current_inferior ();
+  terminal_info *tinfo = get_inflow_inferior_data (inf);
+
+  /* No need to save/restore if the inferior is not sharing GDB's
+     tty.  */
+  if (!sharing_input_terminal (inf))
     return;
 
-  terminal_is_ours = 1;
+  xfree (tinfo->ttystate);
+  tinfo->ttystate = serial_get_tty_state (stdin_serial);
 
-  /* Checking inferior->run_terminal is necessary so that
-     if GDB is running in the background, it won't block trying
-     to do the ioctl()'s below.  Checking gdb_has_a_terminal
-     avoids attempting all the ioctl's when running in batch.  */
+  tinfo->process_group = tcgetpgrp (0);
 
-  inf = current_inferior ();
-  tinfo = get_inflow_inferior_data (inf);
+#ifdef F_GETFL
+  tinfo->tflags = fcntl (0, F_GETFL, 0);
+#endif
+}
+
+/* Switch terminal state to DESIRED_STATE, either is_ours, or
+   is_ours_for_output.  */
 
-  if (tinfo->run_terminal != NULL || gdb_has_a_terminal () == 0)
+static void
+child_terminal_ours_1 (target_terminal_state desired_state)
+{
+  gdb_assert (desired_state != target_terminal_state::is_inferior);
+
+  /* Avoid attempting all the ioctl's when running in batch.  */
+  if (!gdb_has_a_terminal ())
     return;
-  else
+
+  if (gdb_tty_state != desired_state)
     {
       int result ATTRIBUTE_UNUSED;
 
@@ -364,21 +496,13 @@ child_terminal_ours_1 (int output_only)
 	 terminal's pgrp.  */
       scoped_ignore_sigttou ignore_sigttou;
 
-      xfree (tinfo->ttystate);
-      tinfo->ttystate = serial_get_tty_state (stdin_serial);
-
-#ifdef HAVE_TERMIOS_H
-      if (!inf->attach_flag)
-	/* If tcsetpgrp failed in terminal_inferior, this would give us
-	   our process group instead of the inferior's.  See
-	   terminal_inferior for details.  */
-	tinfo->process_group = tcgetpgrp (0);
-#endif
-
       /* Set tty state to our_ttystate.  */
       serial_set_tty_state (stdin_serial, our_terminal_info.ttystate);
 
-      if (job_control)
+      /* If we only want output, then leave the inferior's pgrp in the
+	 foreground, so that Ctrl-C/Ctrl-Z reach the inferior
+	 directly.  */
+      if (job_control && desired_state == target_terminal_state::is_ours)
 	{
 #ifdef HAVE_TERMIOS_H
 	  result = tcsetpgrp (0, our_terminal_info.process_group);
@@ -395,7 +519,7 @@ child_terminal_ours_1 (int output_only)
 #endif /* termios */
 	}
 
-      if (!job_control)
+      if (!job_control && desired_state == target_terminal_state::is_ours)
 	{
 	  signal (SIGINT, sigint_ours);
 #ifdef SIGQUIT
@@ -404,10 +528,92 @@ child_terminal_ours_1 (int output_only)
 	}
 
 #ifdef F_GETFL
-      tinfo->tflags = fcntl (0, F_GETFL, 0);
       result = fcntl (0, F_SETFL, our_terminal_info.tflags);
 #endif
+
+      gdb_tty_state = desired_state;
+    }
+}
+
+/* Interrupt the inferior.  Implementation of target_interrupt for
+   child/native targets.  */
+
+void
+child_interrupt (struct target_ops *self)
+{
+  /* Interrupt the first inferior that has a resumed thread.  */
+  thread_info *thr;
+  thread_info *resumed = NULL;
+  ALL_NON_EXITED_THREADS (thr)
+    {
+      if (thr->executing)
+	{
+	  resumed = thr;
+	  break;
+	}
+      if (thr->suspend.waitstatus_pending_p)
+	resumed = thr;
+    }
+
+  if (resumed != NULL)
+    {
+      /* Note that unlike pressing Ctrl-C on the controlling terminal,
+	 here we only interrupt one process, not the whole process
+	 group.  This is because interrupting a process group (with
+	 either Ctrl-C or with kill(3) with negative PID) sends a
+	 SIGINT to each process in the process group, and we may not
+	 be debugging all processes in the process group.  */
+      kill (resumed->inf->pid, SIGINT);
+    }
+}
+
+/* Pass a Ctrl-C to the inferior as-if a Ctrl-C was pressed while the
+   inferior was in the foreground.  Implementation of
+   target_pass_ctrlc for child/native targets.  */
+
+void
+child_pass_ctrlc (struct target_ops *self)
+{
+  gdb_assert (!target_terminal::is_ours ());
+
+#ifdef HAVE_TERMIOS_H
+  if (job_control)
+    {
+      pid_t term_pgrp = tcgetpgrp (0);
+
+      /* If there's any inferior sharing our terminal, pass the SIGINT
+	 to the terminal's foreground process group.  This acts just
+	 like the user typed a ^C on the terminal while the inferior
+	 was in the foreground.  Note that using a negative process
+	 number in kill() is a System V-ism.  The proper BSD interface
+	 is killpg().  However, all modern BSDs support the System V
+	 interface too.  */
+
+      if (term_pgrp != -1 && term_pgrp != our_terminal_info.process_group)
+	{
+	  kill (-term_pgrp, SIGINT);
+	  return;
+	}
+    }
+#endif
+
+  /* Otherwise, pass the Ctrl-C to the first inferior that was resumed
+     in the foreground.  */
+  inferior *inf;
+  ALL_INFERIORS (inf)
+    {
+      if (inf->terminal_state != target_terminal_state::is_ours)
+	{
+	  gdb_assert (inf->pid != 0);
+
+	  kill (inf->pid, SIGINT);
+	  return;
+	}
     }
+
+  /* If no inferior was resumed in the foreground, then how did the
+     !is_ours assert above pass?  */
+  gdb_assert_not_reached ("no inferior resumed in the fg found");
 }
 
 /* Per-inferior data key.  */
@@ -452,6 +658,8 @@ inflow_inferior_exit (struct inferior *inf)
 {
   struct terminal_info *info;
 
+  inf->terminal_state = target_terminal_state::is_ours;
+
   info = (struct terminal_info *) inferior_data (inf, inflow_inferior_data);
   if (info != NULL)
     {
@@ -482,6 +690,8 @@ copy_terminal_info (struct inferior *to, struct inferior *from)
   if (tinfo_from->ttystate)
     tinfo_to->ttystate
       = serial_copy_tty_state (stdin_serial, tinfo_from->ttystate);
+
+  to->terminal_state = from->terminal_state;
 }
 
 void
@@ -770,8 +980,6 @@ _initialize_inflow (void)
   add_info ("terminal", info_terminal_command,
 	    _("Print inferior's saved terminal status."));
 
-  terminal_is_ours = 1;
-
   /* OK, figure out whether we have job control.  */
   have_job_control ();