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.

25 files changed, 1064 insertions, 202 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index e640902..d951360 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,78 @@
 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.
+
+2018-01-30  Pedro Alves  <palves@redhat.com>
+
 	* linux-nat.c (wait_for_signal): New function.
 	(wait_lwp, linux_nat_wait_1): Use it instead of calling sigsuspend
 	directly.
diff --git a/gdb/config.in b/gdb/config.in
index ad2cc17..aa46f07 100644
--- a/gdb/config.in
+++ b/gdb/config.in
@@ -192,6 +192,9 @@
 /* Define to 1 if you have the `getpagesize' function. */
 #undef HAVE_GETPAGESIZE
 
+/* Define to 1 if you have the `getpgid' function. */
+#undef HAVE_GETPGID
+
 /* Define to 1 if you have the `getrlimit' function. */
 #undef HAVE_GETRLIMIT
 
diff --git a/gdb/configure b/gdb/configure
index a61a73f..81b35af 100755
--- a/gdb/configure
+++ b/gdb/configure
@@ -13212,7 +13212,7 @@ fi
 
 for ac_func in getauxval getrusage getuid getgid \
 		pipe poll pread pread64 pwrite resize_term \
-		sbrk setpgid setpgrp setsid \
+		sbrk getpgid setpgid setpgrp setsid \
 		sigaction sigprocmask sigsetmask socketpair \
 		ttrace wborder wresize setlocale iconvlist libiconvlist btowc \
 		setrlimit getrlimit posix_madvise waitpid \
diff --git a/gdb/configure.ac b/gdb/configure.ac
index e53dda0..125e5f3 100644
--- a/gdb/configure.ac
+++ b/gdb/configure.ac
@@ -1368,7 +1368,7 @@ AC_FUNC_MMAP
 AC_FUNC_VFORK
 AC_CHECK_FUNCS([getauxval getrusage getuid getgid \
 		pipe poll pread pread64 pwrite resize_term \
-		sbrk setpgid setpgrp setsid \
+		sbrk getpgid setpgid setpgrp setsid \
 		sigaction sigprocmask sigsetmask socketpair \
 		ttrace wborder wresize setlocale iconvlist libiconvlist btowc \
 		setrlimit getrlimit posix_madvise waitpid \
diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index 877b6e6..9559e63 100644
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,3 +1,9 @@
+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.
+
 2018-01-19  James Clarke  <jrtc27@jrtc27.com>
 
 	* linux-low.c (handle_extended_wait): Surround call to
diff --git a/gdb/gdbserver/target.c b/gdb/gdbserver/target.c
index 019f974..fe40b94 100644
--- a/gdb/gdbserver/target.c
+++ b/gdb/gdbserver/target.c
@@ -360,8 +360,8 @@ default_breakpoint_kind_from_pc (CORE_ADDR *pcptr)
 
 /* Define it.  */
 
-enum target_terminal::terminal_state target_terminal::terminal_state
-  = target_terminal::terminal_is_ours;
+target_terminal_state target_terminal::m_terminal_state
+  = target_terminal_state::is_ours;
 
 /* See target/target.h.  */
 
diff --git a/gdb/go32-nat.c b/gdb/go32-nat.c
index f36c718..f9a52a7 100644
--- a/gdb/go32-nat.c
+++ b/gdb/go32-nat.c
@@ -937,6 +937,11 @@ go32_terminal_ours (struct target_ops *self)
   }
 }
 
+static void
+go32_pass_ctrlc (struct target_ops *self)
+{
+}
+
 static int
 go32_thread_alive (struct target_ops *ops, ptid_t ptid)
 {
@@ -968,6 +973,7 @@ go32_target (void)
   t->to_terminal_ours_for_output = go32_terminal_ours;
   t->to_terminal_ours = go32_terminal_ours;
   t->to_terminal_info = go32_terminal_info;
+  t->to_pass_ctrlc = go32_pass_ctrlc;
   t->to_kill = go32_kill_inferior;
   t->to_create_inferior = go32_create_inferior;
   t->to_mourn_inferior = go32_mourn_inferior;
diff --git a/gdb/inf-child.c b/gdb/inf-child.c
index 69a149a..6875596 100644
--- a/gdb/inf-child.c
+++ b/gdb/inf-child.c
@@ -408,9 +408,12 @@ inf_child_target (void)
   t->to_remove_breakpoint = memory_remove_breakpoint;
   t->to_terminal_init = child_terminal_init;
   t->to_terminal_inferior = child_terminal_inferior;
+  t->to_terminal_save_inferior = child_terminal_save_inferior;
   t->to_terminal_ours_for_output = child_terminal_ours_for_output;
   t->to_terminal_ours = child_terminal_ours;
   t->to_terminal_info = child_terminal_info;
+  t->to_pass_ctrlc = child_pass_ctrlc;
+  t->to_interrupt = child_interrupt;
   t->to_post_startup_inferior = inf_child_post_startup_inferior;
   t->to_follow_fork = inf_child_follow_fork;
   t->to_can_run = inf_child_can_run;
diff --git a/gdb/inf-ptrace.c b/gdb/inf-ptrace.c
index 72aa334..a290cd8 100644
--- a/gdb/inf-ptrace.c
+++ b/gdb/inf-ptrace.c
@@ -294,19 +294,6 @@ inf_ptrace_kill (struct target_ops *ops)
   target_mourn_inferior (inferior_ptid);
 }
 
-/* Interrupt the inferior.  */
-
-static void
-inf_ptrace_interrupt (struct target_ops *self, ptid_t ptid)
-{
-  /* Send a SIGINT to the process group.  This acts just like the user
-     typed a ^C on the controlling terminal.  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.  */
-  kill (-inferior_process_group (), SIGINT);
-}
-
 /* Return which PID to pass to ptrace in order to observe/control the
    tracee identified by PTID.  */
 
@@ -688,7 +675,6 @@ inf_ptrace_target (void)
   t->to_mourn_inferior = inf_ptrace_mourn_inferior;
   t->to_thread_alive = inf_ptrace_thread_alive;
   t->to_pid_to_str = inf_ptrace_pid_to_str;
-  t->to_interrupt = inf_ptrace_interrupt;
   t->to_xfer_partial = inf_ptrace_xfer_partial;
 #if defined (PT_IO) && defined (PIOD_READ_AUXV)
   t->to_auxv_parse = inf_ptrace_auxv_parse;
diff --git a/gdb/infcmd.c b/gdb/infcmd.c
index 4ad37aa..ccf08bd 100644
--- a/gdb/infcmd.c
+++ b/gdb/infcmd.c
@@ -3033,7 +3033,7 @@ interrupt_target_1 (int all_threads)
   if (non_stop)
     target_stop (ptid);
   else
-    target_interrupt (ptid);
+    target_interrupt ();
 
   /* Tag the thread as having been explicitly requested to stop, so
      other parts of gdb know not to resume this thread automatically,
diff --git a/gdb/inferior.h b/gdb/inferior.h
index a87ffe0..22008a0 100644
--- a/gdb/inferior.h
+++ b/gdb/inferior.h
@@ -129,10 +129,16 @@ extern void child_terminal_ours_for_output (struct target_ops *self);
 
 extern void child_terminal_inferior (struct target_ops *self);
 
+extern void child_terminal_save_inferior (struct target_ops *self);
+
 extern void child_terminal_init (struct target_ops *self);
 
 extern void child_terminal_init_with_pgrp (int pgrp);
 
+extern void child_pass_ctrlc (struct target_ops *self);
+
+extern void child_interrupt (struct target_ops *self);
+
 /* From fork-child.c */
 
 /* Helper function to call STARTUP_INFERIOR with PID and NUM_TRAPS.
@@ -367,6 +373,10 @@ public:
   /* The name of terminal device to use for I/O.  */
   char *terminal = NULL;
 
+  /* The terminal state as set by the last target_terminal::terminal_*
+     call.  */
+  target_terminal_state terminal_state = target_terminal_state::is_ours;
+
   /* Environment to use for running inferior,
      in format described in environ.h.  */
   gdb_environ environment;
diff --git a/gdb/inflow.c b/gdb/inflow.c
index 6984e8f..7c5e904 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 ();
 
diff --git a/gdb/inflow.h b/gdb/inflow.h
index b655bbe..16a78ee 100644
--- a/gdb/inflow.h
+++ b/gdb/inflow.h
@@ -22,9 +22,4 @@
 
 #include <unistd.h>
 
-/* Process group of the current inferior.  */
-#ifdef HAVE_TERMIOS_H
-extern pid_t inferior_process_group (void);
-#endif
-
 #endif /* inflow.h */
diff --git a/gdb/nto-procfs.c b/gdb/nto-procfs.c
index 6408c21..d72bc11 100644
--- a/gdb/nto-procfs.c
+++ b/gdb/nto-procfs.c
@@ -732,7 +732,7 @@ nto_handle_sigint (int signo)
   /* If this doesn't work, try more severe steps.  */
   signal (signo, nto_handle_sigint_twice);
 
-  target_interrupt (inferior_ptid);
+  target_interrupt ();
 }
 
 static ptid_t
@@ -1275,7 +1275,7 @@ procfs_create_inferior (struct target_ops *ops, const char *exec_file,
 }
 
 static void
-procfs_interrupt (struct target_ops *self, ptid_t ptid)
+procfs_interrupt (struct target_ops *self)
 {
   devctl (ctl_fd, DCMD_PROC_STOP, NULL, 0, 0);
 }
diff --git a/gdb/procfs.c b/gdb/procfs.c
index 2d5ec65..374faa9 100644
--- a/gdb/procfs.c
+++ b/gdb/procfs.c
@@ -89,7 +89,6 @@ static void procfs_attach (struct target_ops *, const char *, int);
 static void procfs_detach (struct target_ops *, const char *, int);
 static void procfs_resume (struct target_ops *,
 			   ptid_t, int, enum gdb_signal);
-static void procfs_interrupt (struct target_ops *self, ptid_t);
 static void procfs_files_info (struct target_ops *);
 static void procfs_fetch_registers (struct target_ops *,
 				    struct regcache *, int);
@@ -172,7 +171,6 @@ procfs_target (void)
   t->to_xfer_partial = procfs_xfer_partial;
   t->to_pass_signals = procfs_pass_signals;
   t->to_files_info = procfs_files_info;
-  t->to_interrupt = procfs_interrupt;
 
   t->to_update_thread_list = procfs_update_thread_list;
   t->to_thread_alive = procfs_thread_alive;
@@ -2836,16 +2834,6 @@ procfs_files_info (struct target_ops *ignore)
 		   target_pid_to_str (inferior_ptid));
 }
 
-/* Stop the child process asynchronously, as when the gdb user types
-   control-c or presses a "stop" button.  Works by sending
-   kill(SIGINT) to the child's process group.  */
-
-static void
-procfs_interrupt (struct target_ops *self, ptid_t ptid)
-{
-  kill (-inferior_process_group (), SIGINT);
-}
-
 /* Make it die.  Wait for it to die.  Clean up after it.  Note: this
    should only be applied to the real process, not to an LWP, because
    of the check for parent-process.  If we need this to work for an
diff --git a/gdb/remote.c b/gdb/remote.c
index 74d18f7..b320ee0 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -4913,7 +4913,7 @@ remote_serial_quit_handler (void)
       /* All-stop protocol, and blocked waiting for stop reply.  Send
 	 an interrupt request.  */
       else if (!target_terminal::is_ours () && rs->waiting_for_stop_reply)
-	target_interrupt (inferior_ptid);
+	target_interrupt ();
       else
 	rs->got_ctrlc_during_io = 1;
     }
@@ -6164,7 +6164,7 @@ remote_stop (struct target_ops *self, ptid_t ptid)
 /* Implement the to_interrupt function for the remote targets.  */
 
 static void
-remote_interrupt (struct target_ops *self, ptid_t ptid)
+remote_interrupt (struct target_ops *self)
 {
   if (remote_debug)
     fprintf_unfiltered (gdb_stdlog, "remote_interrupt called\n");
@@ -6193,7 +6193,7 @@ remote_pass_ctrlc (struct target_ops *self)
   else if (rs->ctrlc_pending_p)
     interrupt_query ();
   else
-    target_interrupt (inferior_ptid);
+    target_interrupt ();
 }
 
 /* Ask the user what to do when an interrupt is received.  */
diff --git a/gdb/target-delegates.c b/gdb/target-delegates.c
index bc84791..95ccef4 100644
--- a/gdb/target-delegates.c
+++ b/gdb/target-delegates.c
@@ -922,6 +922,28 @@ debug_terminal_inferior (struct target_ops *self)
 }
 
 static void
+delegate_terminal_save_inferior (struct target_ops *self)
+{
+  self = self->beneath;
+  self->to_terminal_save_inferior (self);
+}
+
+static void
+tdefault_terminal_save_inferior (struct target_ops *self)
+{
+}
+
+static void
+debug_terminal_save_inferior (struct target_ops *self)
+{
+  fprintf_unfiltered (gdb_stdlog, "-> %s->to_terminal_save_inferior (...)\n", debug_target.to_shortname);
+  debug_target.to_terminal_save_inferior (&debug_target);
+  fprintf_unfiltered (gdb_stdlog, "<- %s->to_terminal_save_inferior (", debug_target.to_shortname);
+  target_debug_print_struct_target_ops_p (&debug_target);
+  fputs_unfiltered (")\n", gdb_stdlog);
+}
+
+static void
 delegate_terminal_ours_for_output (struct target_ops *self)
 {
   self = self->beneath;
@@ -1639,26 +1661,24 @@ debug_stop (struct target_ops *self, ptid_t arg1)
 }
 
 static void
-delegate_interrupt (struct target_ops *self, ptid_t arg1)
+delegate_interrupt (struct target_ops *self)
 {
   self = self->beneath;
-  self->to_interrupt (self, arg1);
+  self->to_interrupt (self);
 }
 
 static void
-tdefault_interrupt (struct target_ops *self, ptid_t arg1)
+tdefault_interrupt (struct target_ops *self)
 {
 }
 
 static void
-debug_interrupt (struct target_ops *self, ptid_t arg1)
+debug_interrupt (struct target_ops *self)
 {
   fprintf_unfiltered (gdb_stdlog, "-> %s->to_interrupt (...)\n", debug_target.to_shortname);
-  debug_target.to_interrupt (&debug_target, arg1);
+  debug_target.to_interrupt (&debug_target);
   fprintf_unfiltered (gdb_stdlog, "<- %s->to_interrupt (", debug_target.to_shortname);
   target_debug_print_struct_target_ops_p (&debug_target);
-  fputs_unfiltered (", ", gdb_stdlog);
-  target_debug_print_ptid_t (arg1);
   fputs_unfiltered (")\n", gdb_stdlog);
 }
 
@@ -4248,6 +4268,8 @@ install_delegators (struct target_ops *ops)
     ops->to_terminal_init = delegate_terminal_init;
   if (ops->to_terminal_inferior == NULL)
     ops->to_terminal_inferior = delegate_terminal_inferior;
+  if (ops->to_terminal_save_inferior == NULL)
+    ops->to_terminal_save_inferior = delegate_terminal_save_inferior;
   if (ops->to_terminal_ours_for_output == NULL)
     ops->to_terminal_ours_for_output = delegate_terminal_ours_for_output;
   if (ops->to_terminal_ours == NULL)
@@ -4530,6 +4552,7 @@ install_dummy_methods (struct target_ops *ops)
   ops->to_can_do_single_step = tdefault_can_do_single_step;
   ops->to_terminal_init = tdefault_terminal_init;
   ops->to_terminal_inferior = tdefault_terminal_inferior;
+  ops->to_terminal_save_inferior = tdefault_terminal_save_inferior;
   ops->to_terminal_ours_for_output = tdefault_terminal_ours_for_output;
   ops->to_terminal_ours = tdefault_terminal_ours;
   ops->to_terminal_info = default_terminal_info;
@@ -4690,6 +4713,7 @@ init_debug_target (struct target_ops *ops)
   ops->to_can_do_single_step = debug_can_do_single_step;
   ops->to_terminal_init = debug_terminal_init;
   ops->to_terminal_inferior = debug_terminal_inferior;
+  ops->to_terminal_save_inferior = debug_terminal_save_inferior;
   ops->to_terminal_ours_for_output = debug_terminal_ours_for_output;
   ops->to_terminal_ours = debug_terminal_ours;
   ops->to_terminal_info = debug_terminal_info;
diff --git a/gdb/target.c b/gdb/target.c
index ce630f4..ea2ad3f 100644
--- a/gdb/target.c
+++ b/gdb/target.c
@@ -47,6 +47,7 @@
 #include "event-top.h"
 #include <algorithm>
 #include "byte-vector.h"
+#include "terminal.h"
 
 static void generic_tls_error (void) ATTRIBUTE_NORETURN;
 
@@ -431,8 +432,8 @@ target_load (const char *arg, int from_tty)
 
 /* Define it.  */
 
-enum target_terminal::terminal_state target_terminal::terminal_state
-  = target_terminal::terminal_is_ours;
+target_terminal_state target_terminal::m_terminal_state
+  = target_terminal_state::is_ours;
 
 /* See target/target.h.  */
 
@@ -441,7 +442,7 @@ target_terminal::init (void)
 {
   (*current_target.to_terminal_init) (&current_target);
 
-  terminal_state = terminal_is_ours;
+  m_terminal_state = target_terminal_state::is_ours;
 }
 
 /* See target/target.h.  */
@@ -463,13 +464,56 @@ target_terminal::inferior (void)
   if (ui != main_ui)
     return;
 
-  if (terminal_state == terminal_is_inferior)
-    return;
-
   /* If GDB is resuming the inferior in the foreground, install
      inferior's terminal modes.  */
-  (*current_target.to_terminal_inferior) (&current_target);
-  terminal_state = terminal_is_inferior;
+
+  struct inferior *inf = current_inferior ();
+
+  if (inf->terminal_state != target_terminal_state::is_inferior)
+    {
+      (*current_target.to_terminal_inferior) (&current_target);
+      inf->terminal_state = target_terminal_state::is_inferior;
+    }
+
+  m_terminal_state = target_terminal_state::is_inferior;
+
+  /* If the user hit C-c before, pretend that it was hit right
+     here.  */
+  if (check_quit_flag ())
+    target_pass_ctrlc ();
+}
+
+/* See target/target.h.  */
+
+void
+target_terminal::restore_inferior (void)
+{
+  struct ui *ui = current_ui;
+
+  /* See target_terminal::inferior().  */
+  if (ui->prompt_state != PROMPT_BLOCKED || ui != main_ui)
+    return;
+
+  /* Restore the terminal settings of inferiors that were in the
+     foreground but are now ours_for_output due to a temporary
+     target_target::ours_for_output() call.  */
+
+  {
+    scoped_restore_current_inferior restore_inferior;
+    struct inferior *inf;
+
+    ALL_INFERIORS (inf)
+      {
+	if (inf->terminal_state == target_terminal_state::is_ours_for_output)
+	  {
+	    set_current_inferior (inf);
+	    (*current_target.to_terminal_inferior) (&current_target);
+	    inf->terminal_state = target_terminal_state::is_inferior;
+	  }
+      }
+  }
+
+  m_terminal_state = target_terminal_state::is_inferior;
 
   /* If the user hit C-c before, pretend that it was hit right
      here.  */
@@ -477,6 +521,50 @@ target_terminal::inferior (void)
     target_pass_ctrlc ();
 }
 
+/* Switch terminal state to DESIRED_STATE, either is_ours, or
+   is_ours_for_output.  */
+
+static void
+target_terminal_is_ours_kind (target_terminal_state desired_state)
+{
+  scoped_restore_current_inferior restore_inferior;
+  struct inferior *inf;
+
+  /* Must do this in two passes.  First, have all inferiors save the
+     current terminal settings.  Then, after all inferiors have add a
+     chance to safely save the terminal settings, restore GDB's
+     terminal settings.  */
+
+  ALL_INFERIORS (inf)
+    {
+      if (inf->terminal_state == target_terminal_state::is_inferior)
+	{
+	  set_current_inferior (inf);
+	  (*current_target.to_terminal_save_inferior) (&current_target);
+	}
+    }
+
+  ALL_INFERIORS (inf)
+    {
+      /* Note we don't check is_inferior here like above because we
+	 need to handle 'is_ours_for_output -> is_ours' too.  Careful
+	 to never transition from 'is_ours' to 'is_ours_for_output',
+	 though.  */
+      if (inf->terminal_state != target_terminal_state::is_ours
+	  && inf->terminal_state != desired_state)
+	{
+	  set_current_inferior (inf);
+	  if (desired_state == target_terminal_state::is_ours)
+	    (*current_target.to_terminal_ours) (&current_target);
+	  else if (desired_state == target_terminal_state::is_ours_for_output)
+	    (*current_target.to_terminal_ours_for_output) (&current_target);
+	  else
+	    gdb_assert_not_reached ("unhandled desired state");
+	  inf->terminal_state = desired_state;
+	}
+    }
+}
+
 /* See target/target.h.  */
 
 void
@@ -488,11 +576,11 @@ target_terminal::ours ()
   if (ui != main_ui)
     return;
 
-  if (terminal_state == terminal_is_ours)
+  if (m_terminal_state == target_terminal_state::is_ours)
     return;
 
-  (*current_target.to_terminal_ours) (&current_target);
-  terminal_state = terminal_is_ours;
+  target_terminal_is_ours_kind (target_terminal_state::is_ours);
+  m_terminal_state = target_terminal_state::is_ours;
 }
 
 /* See target/target.h.  */
@@ -506,10 +594,11 @@ target_terminal::ours_for_output ()
   if (ui != main_ui)
     return;
 
-  if (terminal_state != terminal_is_inferior)
+  if (!target_terminal::is_inferior ())
     return;
-  (*current_target.to_terminal_ours_for_output) (&current_target);
-  terminal_state = terminal_is_ours_for_output;
+
+  target_terminal_is_ours_kind (target_terminal_state::is_ours_for_output);
+  target_terminal::m_terminal_state = target_terminal_state::is_ours_for_output;
 }
 
 /* See target/target.h.  */
@@ -3332,7 +3421,7 @@ target_stop (ptid_t ptid)
 }
 
 void
-target_interrupt (ptid_t ptid)
+target_interrupt ()
 {
   if (!may_stop)
     {
@@ -3340,7 +3429,7 @@ target_interrupt (ptid_t ptid)
       return;
     }
 
-  (*current_target.to_interrupt) (&current_target, ptid);
+  (*current_target.to_interrupt) (&current_target);
 }
 
 /* See target.h.  */
@@ -3356,7 +3445,7 @@ target_pass_ctrlc (void)
 void
 default_target_pass_ctrlc (struct target_ops *ops)
 {
-  target_interrupt (inferior_ptid);
+  target_interrupt ();
 }
 
 /* See target/target.h.  */
diff --git a/gdb/target.h b/gdb/target.h
index 52361ba..096252a 100644
--- a/gdb/target.h
+++ b/gdb/target.h
@@ -561,6 +561,8 @@ struct target_ops
       TARGET_DEFAULT_IGNORE ();
     void (*to_terminal_inferior) (struct target_ops *)
       TARGET_DEFAULT_IGNORE ();
+    void (*to_terminal_save_inferior) (struct target_ops *)
+      TARGET_DEFAULT_IGNORE ();
     void (*to_terminal_ours_for_output) (struct target_ops *)
       TARGET_DEFAULT_IGNORE ();
     void (*to_terminal_ours) (struct target_ops *)
@@ -640,7 +642,7 @@ struct target_ops
       TARGET_DEFAULT_RETURN (NULL);
     void (*to_stop) (struct target_ops *, ptid_t)
       TARGET_DEFAULT_IGNORE ();
-    void (*to_interrupt) (struct target_ops *, ptid_t)
+    void (*to_interrupt) (struct target_ops *)
       TARGET_DEFAULT_IGNORE ();
     void (*to_pass_ctrlc) (struct target_ops *)
       TARGET_DEFAULT_FUNC (default_target_pass_ctrlc);
@@ -1690,16 +1692,18 @@ extern void target_update_thread_list (void);
 
 extern void target_stop (ptid_t ptid);
 
-/* Interrupt the target just like the user typed a ^C on the
-   inferior's controlling terminal.  (For instance, under Unix, this
-   should act like SIGINT).  This function is asynchronous.  */
+/* Interrupt the target.  Unlike target_stop, this does not specify
+   which thread/process reports the stop.  For most target this acts
+   like raising a SIGINT, though that's not absolutely required.  This
+   function is asynchronous.  */
 
-extern void target_interrupt (ptid_t ptid);
+extern void target_interrupt ();
 
 /* Pass a ^C, as determined to have been pressed by checking the quit
-   flag, to the target.  Normally calls target_interrupt, but remote
-   targets may take the opportunity to detect the remote side is not
-   responding and offer to disconnect.  */
+   flag, to the target, as if the user had typed the ^C on the
+   inferior's controlling terminal while the inferior was in the
+   foreground.  Remote targets may take the opportunity to detect the
+   remote side is not responding and offer to disconnect.  */
 
 extern void target_pass_ctrlc (void);
 
diff --git a/gdb/target/target.h b/gdb/target/target.h
index 5571e16..879e730 100644
--- a/gdb/target/target.h
+++ b/gdb/target/target.h
@@ -95,6 +95,21 @@ extern void target_mourn_inferior (ptid_t ptid);
 
 extern int target_supports_multi_process (void);
 
+/* Possible terminal states.  */
+
+enum class target_terminal_state
+  {
+    /* The inferior's terminal settings are in effect.  */
+    is_inferior = 0,
+
+    /* Some of our terminal settings are in effect, enough to get
+       proper output.  */
+    is_ours_for_output = 1,
+
+    /* Our terminal settings are in effect, for output and input.  */
+    is_ours = 2
+  };
+
 /* Represents the state of the target terminal.  */
 class target_terminal
 {
@@ -108,9 +123,9 @@ public:
      before we actually run the inferior.  */
   static void init ();
 
-  /* Put the inferior's terminal settings into effect.  This is
-     preparation for starting or resuming the inferior.  This is a no-op
-     unless called with the main UI as current UI.  */
+  /* Put the current inferior's terminal settings into effect.  This
+     is preparation for starting or resuming the inferior.  This is a
+     no-op unless called with the main UI as current UI.  */
   static void inferior ();
 
   /* Put our terminal settings into effect.  First record the inferior's
@@ -125,40 +140,34 @@ public:
      UI as current UI.  */
   static void ours_for_output ();
 
+  /* Restore terminal settings of inferiors that are in
+     is_ours_for_output state back to "inferior".  Used when we need
+     to temporarily switch to is_ours_for_output state.  */
+  static void restore_inferior ();
+
   /* Returns true if the terminal settings of the inferior are in
      effect.  */
   static bool is_inferior ()
   {
-    return terminal_state == terminal_is_inferior;
+    return m_terminal_state == target_terminal_state::is_inferior;
   }
 
   /* Returns true if our terminal settings are in effect.  */
   static bool is_ours ()
   {
-    return terminal_state == terminal_is_ours;
+    return m_terminal_state == target_terminal_state::is_ours;
+  }
+
+  /* Returns true if our terminal settings are in effect.  */
+  static bool is_ours_for_output ()
+  {
+    return m_terminal_state == target_terminal_state::is_ours_for_output;
   }
 
   /* Print useful information about our terminal status, if such a thing
      exists.  */
   static void info (const char *arg, int from_tty);
 
-private:
-
-  /* Possible terminal states.  */
-
-  enum terminal_state
-    {
-     /* The inferior's terminal settings are in effect.  */
-     terminal_is_inferior = 0,
-
-     /* Some of our terminal settings are in effect, enough to get
-	proper output.  */
-     terminal_is_ours_for_output = 1,
-
-     /* Our terminal settings are in effect, for output and input.  */
-     terminal_is_ours = 2
-    };
-
 public:
 
   /* A class that restores the state of the terminal to the current
@@ -168,7 +177,7 @@ public:
   public:
 
     scoped_restore_terminal_state ()
-      : m_state (terminal_state)
+      : m_state (m_terminal_state)
     {
     }
 
@@ -176,14 +185,14 @@ public:
     {
       switch (m_state)
 	{
-	case terminal_is_ours:
+	case target_terminal_state::is_ours:
 	  ours ();
 	  break;
-	case terminal_is_ours_for_output:
+	case target_terminal_state::is_ours_for_output:
 	  ours_for_output ();
 	  break;
-	case terminal_is_inferior:
-	  inferior ();
+	case target_terminal_state::is_inferior:
+	  restore_inferior ();
 	  break;
 	}
     }
@@ -192,12 +201,12 @@ public:
 
   private:
 
-    target_terminal::terminal_state m_state;
+    target_terminal_state m_state;
   };
 
 private:
 
-  static terminal_state terminal_state;
+  static target_terminal_state m_terminal_state;
 };
 
 #endif /* TARGET_COMMON_H */
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 52a689f..19b3eda 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,11 @@
+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.
+
 2018-01-30  Joel Brobecker  <brobecker@adacore.com>
 
 	* gdb.base/break.exp: Save the location where the breakpoint
diff --git a/gdb/testsuite/gdb.base/interrupt-daemon.c b/gdb/testsuite/gdb.base/interrupt-daemon.c
new file mode 100644
index 0000000..5074d7b
--- /dev/null
+++ b/gdb/testsuite/gdb.base/interrupt-daemon.c
@@ -0,0 +1,67 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2017 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <unistd.h>
+#include <stdlib.h>
+#include <assert.h>
+
+static void
+daemon_main (void)
+{
+}
+
+int
+main ()
+{
+  pid_t child;
+
+  alarm (60);
+
+  /* Normally we're a progress group leader at this point, so can't
+     create a session.  Fork so the child can create a new
+     session.  */
+  child = fork ();
+  if (child == -1)
+    return 1;
+  else if (child != 0)
+    return 0;
+  else
+    {
+      /* In child.  Switch to a new session.  */
+      pid_t session = setsid ();
+      if (session == -1)
+	return 1;
+
+      /* Fork again, so that the grand child (what we want to debug)
+	 can't accidentally acquire a controlling terminal, because
+	 it's not a session leader.  We're not opening any file here,
+	 but this is representative of what daemons do.  */
+      child = fork ();
+      if (child == -1)
+	return 1;
+      else if (child != 0)
+	return 0;
+
+      /* In grandchild.  */
+      daemon_main ();
+
+      while (1)
+	sleep (1);
+    }
+
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.base/interrupt-daemon.exp b/gdb/testsuite/gdb.base/interrupt-daemon.exp
new file mode 100644
index 0000000..ca3eecb
--- /dev/null
+++ b/gdb/testsuite/gdb.base/interrupt-daemon.exp
@@ -0,0 +1,89 @@
+# Copyright 2017 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Make sure that we can interrupt an inferior that forks and moves to
+# its own session.
+
+standard_testfile
+
+if {[build_executable "failed to build" $testfile $srcfile {debug}]} {
+    return -1
+}
+
+# The test proper.
+
+proc do_test {} {
+    global binfile
+    global gdb_prompt
+
+    clean_restart $binfile
+
+    gdb_test "set follow-fork-mode child" ".*"
+
+    if ![runto "daemon_main"] {
+	fail "can't run to daemon_main function"
+	return
+    }
+
+    with_test_prefix "fg" {
+	global gdb_prompt
+
+	set test "continue"
+	gdb_test_multiple $test $test {
+	    -re "Continuing" {
+		pass $test
+	    }
+	}
+
+	after 200
+
+	send_gdb "\003"
+
+	set test "ctrl-c stops process"
+	gdb_test_multiple "" $test {
+	    -re "received signal SIGINT.*\r\n$gdb_prompt $" {
+		pass $test
+	    }
+	}
+    }
+
+    with_test_prefix "bg" {
+
+	set test "continue&"
+	gdb_test_multiple "continue&" $test {
+	    -re "Continuing\\.\r\n$gdb_prompt " {
+		pass $test
+	    }
+	}
+
+	after 200
+
+	set test "interrupt"
+	gdb_test_multiple $test $test {
+	    -re "$gdb_prompt " {
+		pass $test
+	    }
+	}
+
+	set test "interrupt cmd stops process"
+	gdb_test_multiple "" $test {
+	    -re "received signal SIGINT" {
+		pass $test
+	    }
+	}
+    }
+}
+
+do_test
diff --git a/gdb/testsuite/gdb.multi/multi-term-settings.c b/gdb/testsuite/gdb.multi/multi-term-settings.c
new file mode 100644
index 0000000..c96779e
--- /dev/null
+++ b/gdb/testsuite/gdb.multi/multi-term-settings.c
@@ -0,0 +1,52 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2017 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* This program is intended to be started outside of gdb, and then
+   attached to by gdb.  It loops for a while, but not forever.  */
+
+#include <unistd.h>
+#include <stdio.h>
+#include <sys/types.h>
+#include <termios.h>
+#include <unistd.h>
+#include <signal.h>
+
+int
+main ()
+{
+  /* In case we inherit SIG_IGN.  */
+  signal (SIGTTOU, SIG_DFL);
+
+  alarm (30);
+
+  int count = 0;
+  while (1)
+    {
+      struct termios termios;
+
+      printf ("pid=%ld, count=%d\n", (long) getpid (), count++);
+
+      /* This generates a SIGTTOU if our progress group is not in the
+	 foreground.  */
+      tcgetattr (0, &termios);
+      tcsetattr (0, TCSANOW, &termios);
+
+      usleep (100000);
+    }
+
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.multi/multi-term-settings.exp b/gdb/testsuite/gdb.multi/multi-term-settings.exp
new file mode 100644
index 0000000..7245b84
--- /dev/null
+++ b/gdb/testsuite/gdb.multi/multi-term-settings.exp
@@ -0,0 +1,242 @@
+# This testcase is part of GDB, the GNU debugger.
+
+# Copyright 2017 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# This testcase exercises GDB's terminal ownership management
+# (terminal_ours/terminal_inferior, etc.) when debugging multiple
+# inferiors.  It tests debugging multiple inferiors started with
+# different combinations of 'run'/'run+tty'/'attach', and ensures that
+# the process that is sharing GDB's terminal/session is properly made
+# the GDB terminal's foregound process group (i.e., "given the
+# terminal").
+
+standard_testfile
+
+if ![can_spawn_for_attach] {
+    return 0
+}
+
+if [build_executable "failed to prepare" $testfile $srcfile {debug}] {
+    return -1
+}
+
+# Start the programs running and then wait for a bit, to be sure that
+# they can be attached to.  We start these processes upfront in order
+# to reuse them for the different iterations.  This makes the testcase
+# faster, compared to calling spawn_wait_for_attach for each iteration
+# in the testing matrix.
+
+set spawn_id_list [spawn_wait_for_attach [list $binfile $binfile]]
+set attach_spawn_id1 [lindex $spawn_id_list 0]
+set attach_spawn_id2 [lindex $spawn_id_list 1]
+set attach_pid1 [spawn_id_get_pid $attach_spawn_id1]
+set attach_pid2 [spawn_id_get_pid $attach_spawn_id2]
+
+# Create inferior WHICH_INF.  INF_HOW is how to create it.  This can
+# be one of:
+#
+#  - "run" - for "run" command.
+#  - "tty" - for "run" + "tty TTY".
+#  - "attach" - for attaching to an existing process.
+proc create_inferior {which_inf inf_how} {
+    global binfile
+
+    # Run to main and delete breakpoints.
+    proc my_runto_main {} {
+	if ![runto_main] {
+	    fail "run to main"
+	    return 0
+	} else {
+	    # Delete breakpoints otherwise GDB would try to step over
+	    # the breakpoint at 'main' without resuming the other
+	    # inferior, possibly masking the issue we're trying to
+	    # test.
+	    delete_breakpoints
+	    return 1
+	}
+    }
+
+    if {$inf_how == "run"} {
+	if [my_runto_main] {
+	    global inferior_spawn_id
+	    return $inferior_spawn_id
+	}
+    } elseif {$inf_how == "tty"} {
+	# Create the new PTY for the inferior.
+	spawn -pty
+	set inf_spawn_id $spawn_id
+	set inf_tty_name $spawn_out(slave,name)
+	gdb_test_no_output "tty $inf_tty_name" "tty TTY"
+
+	if [my_runto_main] {
+	    return $inf_spawn_id
+	}
+    } elseif {$inf_how == "attach"} {
+
+	# Reuse the inferiors spawned at the start of the testcase (to
+	# avoid having to wait the delay imposed by
+	# spawn_wait_for_attach).
+	global attach_spawn_id$which_inf
+	set test_spawn_id [set attach_spawn_id$which_inf]
+	set testpid [spawn_id_get_pid $test_spawn_id]
+	if {[gdb_test "attach $testpid" \
+		 "Attaching to program: .*, process $testpid.*(in|at).*" \
+		 "attach"] == 0} {
+	    return $test_spawn_id
+	}
+    } else {
+	error "unhandled inf_how: $inf_how"
+    }
+
+    return ""
+}
+
+# Print debug output.
+
+proc send_debug {str} {
+    # Uncomment for debugging.
+    #send_user $str
+}
+
+# The core of the testcase.  See intro.  Creates two inferiors that
+# both loop changing their terminal's settings and printing output,
+# and checks whether they receive SIGTTOU.  INF1_HOW and INF2_HOW
+# indicate how inferiors 1 and 2 should be created, respectively.  See
+# 'create_inferior' above for what arguments these parameters accept.
+
+proc coretest {inf1_how inf2_how} {
+    global binfile
+    global inferior_spawn_id
+    global gdb_spawn_id
+    global decimal
+
+    clean_restart $binfile
+
+    set inf1_spawn_id [create_inferior 1 $inf1_how]
+
+    set num 2
+    gdb_test "add-inferior" "Added inferior $num.*" \
+	"add empty inferior $num"
+    gdb_test "inferior $num" "Switching to inferior $num.*" \
+	"switch to inferior $num"
+    gdb_file_cmd ${binfile}
+
+    set inf2_spawn_id [create_inferior 2 $inf2_how]
+
+    gdb_test_no_output "set schedule-multiple on"
+
+    # "run" makes each inferior be a process group leader.  When we
+    # run both inferiors in GDB's terminal/session, only one can end
+    # up as the terminal's foreground process group, so it's expected
+    # that the other receives a SIGTTOU.
+    set expect_ttou [expr {$inf1_how == "run" && $inf2_how == "run"}]
+
+    global gdb_prompt
+
+    set any "\[^\r\n\]*"
+
+    set pid1 -1
+    set pid2 -1
+
+    set test "info inferiors"
+    gdb_test_multiple $test $test {
+	-re "1${any}process ($decimal)${any}\r\n" {
+	    set pid1 $expect_out(1,string)
+	    send_debug "pid1=$pid1\n"
+	    exp_continue
+	}
+	-re "2${any}process ($decimal)${any}\r\n" {
+	    set pid2 $expect_out(1,string)
+	    send_debug "pid2=$pid2\n"
+	    exp_continue
+	}
+	-re "$gdb_prompt $" {
+	    pass $test
+	}
+    }
+
+    # Helper for the gdb_test_multiple call below.  Issues a PASS if
+    # we've seen each inferior print at least 3 times, otherwise
+    # continues waiting for inferior output.
+    proc pass_or_exp_continue {} {
+	uplevel 1 {
+	    if {$count1 >= 3 && $count2 >= 3} {
+		if $expect_ttou {
+		    fail "$test (expected SIGTTOU)"
+		} else {
+		    pass $test
+		}
+	    } else {
+		exp_continue
+	    }
+	}
+    }
+
+    set infs_spawn_ids [list $inf1_spawn_id $inf2_spawn_id]
+    send_debug "infs_spawn_ids=$infs_spawn_ids\n"
+
+    set count1 0
+    set count2 0
+
+    set test "continue"
+    gdb_test_multiple $test $test {
+	-i $infs_spawn_ids -re "pid=$pid1, count=" {
+	    incr count1
+	    pass_or_exp_continue
+	}
+	-i $infs_spawn_ids -re "pid=$pid2, count=" {
+	    incr count2
+	    pass_or_exp_continue
+	}
+	-i $gdb_spawn_id -re "received signal SIGTTOU.*$gdb_prompt " {
+	    if $expect_ttou {
+		pass "$test (expected SIGTTOU)"
+	    } else {
+		fail "$test (SIGTTOU)"
+	    }
+	}
+    }
+
+    send_gdb "\003"
+    if {$expect_ttou} {
+	gdb_test "" "Quit" "stop with control-c"
+    } else {
+	gdb_test "" "received signal SIGINT.*" "stop with control-c"
+    }
+
+    # Useful for debugging in case the Ctrl-C above fails.
+    gdb_test "info inferiors"
+    gdb_test "info threads"
+}
+
+set how_modes {"run" "attach" "tty"}
+
+foreach_with_prefix inf1_how $how_modes {
+    foreach_with_prefix inf2_how $how_modes {
+	if {($inf1_how == "tty" || $inf2_how == "tty")
+	    && [target_info gdb_protocol] == "extended-remote"} {
+	    # No way to specify the inferior's tty in the remote
+	    # protocol.
+	    unsupported "no support for \"tty\" in the RSP"
+	    continue
+	}
+
+	coretest $inf1_how $inf2_how
+    }
+}
+
+kill_wait_spawned_process $attach_spawn_id1
+kill_wait_spawned_process $attach_spawn_id2