gdb/:

    * remote.c (interrupt_sequence_control_c)
        (interrupt_sequence_break, interrupt_sequence_break_g)
        (interrupt_sequence_modes): New constants.
        (interrupt_sequence_mode, interrupt_on_connect): New variable.
        (show_interrupt_sequence): New function.
        (set_remotebreak, show_remotebreak): New function.
        (send_interrupt_sequence): New function.
        (remote_start_remote): Call send_interrupt_sequence if
        interrupt_on_connect is true.
        (remote_stop_as): Call send_interrupt_sequence.
        (_initialize_remote): Add interrupt-sequence and interrupt-on-connect,
        modify remotebreak to call set_remotebreak and show_remotebreak.
        * NEWS: Add entry for "set/show remote interrupt-sequence" and
        "set/show remote interrupt-on-connect". Also mention that
        "set/show remotebreak" is now deprecated.

    gdb/doc/:

        * gdb.texinfo (Remote Configuration): Add "set/show remote
        interrupt-sequence" and "set/show remote interrupt-on-connect" command.

3 files changed, 169 insertions, 14 deletions

diff --git a/gdb/NEWS b/gdb/NEWS
index b95edba..d20d8e6 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -37,6 +37,24 @@ remove-inferior ID
 maint info program-spaces
   List the program spaces loaded into GDB.
 
+set remote interrupt-sequence [Ctrl-C | BREAK | BREAK-g]
+show remote interrupt-sequence
+  Allow the user to select one of ^C, a BREAK signal or BREAK-g
+  as the sequence to the remote target in order to interrupt the execution.
+  Ctrl-C is a default.  Some system prefers BREAK which is high level of
+  serial line for some certain time.  Linux kernel prefers BREAK-g, a.k.a
+  Magic SysRq g.  It is BREAK signal and character 'g'.
+
+set remote interrupt-on-connect [on | off]
+show remote interrupt-on-connect
+  When interrupt-on-connect is ON, gdb sends interrupt-sequence to
+  remote target when gdb connects to it.  This is needed when you debug
+  Linux kernel.
+
+set remotebreak [on | off]
+show remotebreak
+Deprecated.  Use "set/show remote interrupt-sequence" instead.
+
 * New options
 
 set follow-exec-mode new|same
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 6a74aeb..aa28bc3 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -15234,6 +15234,34 @@ extended-remote}.  This should be set to a filename valid on the
 target system.  If it is not set, the target will use a default
 filename (e.g.@: the last program run).
 
+@item set remote interrupt-sequence
+@cindex interrupt remote programs
+@cindex select Ctrl-C, BREAK or BREAK-g
+Allow the user to select one of @samp{Ctrl-C}, a @code{BREAK} or
+@samp{BREAK-g} as the
+sequence to the remote target in order to interrupt the execution.
+@samp{Ctrl-C} is a default.  Some system prefers @code{BREAK} which
+is high level of serial line for some certain time.
+Linux kernel prefers @samp{BREAK-g}, a.k.a Magic SysRq g.
+It is @code{BREAK} signal followed by character @code{g}.
+
+@item show interrupt-sequence
+Show which of @samp{Ctrl-C}, @code{BREAK} or @code{BREAK-g}
+is sent by @value{GDBN} to interrupt the remote program.
+@code{BREAK-g} is BREAK signal followed by @code{g} and
+also known as Magic SysRq g.
+
+@item set remote interrupt-on-connect
+@cindex send interrupt-sequence on start
+Specify whether interrupt-sequence is sent to remote target when
+@value{GDBN} connects to it.  This is mostly needed when you debug
+Linux kernel.  Linux kernel expects @code{BREAK} followed by @code{g}
+which is known as Magic SysRq g in order to connect @value{GDBN}.
+
+@item show interrupt-on-connect
+Show whether interrupt-sequence is sent
+to remote target when @value{GDBN} connects to it.
+
 @kindex set tcp
 @kindex show tcp
 @item set tcp auto-retry on
@@ -30084,9 +30112,9 @@ or -1 if an error occurs.  @var{pathname} is a string.
 @cindex interrupts (remote protocol)
 
 When a program on the remote target is running, @value{GDBN} may
-attempt to interrupt it by sending a @samp{Ctrl-C} or a @code{BREAK},
-control of which is specified via @value{GDBN}'s @samp{remotebreak}
-setting (@pxref{set remotebreak}).
+attempt to interrupt it by sending a @samp{Ctrl-C}, @code{BREAK} or
+a @code{BREAK} followed by @code{g},
+control of which is specified via @value{GDBN}'s @samp{interrupt-sequence}.
 
 The precise meaning of @code{BREAK} is defined by the transport
 mechanism and may, in fact, be undefined.  @value{GDBN} does not
@@ -30103,6 +30131,10 @@ and does @emph{not} represent an interrupt.  E.g., an @samp{X} packet
 (@pxref{X packet}), used for binary downloads, may include an unescaped
 @code{0x03} as part of its packet.
 
+@code{BREAK} followed by @code{g} is also known as Magic SysRq g.
+When Linux kernel receives this sequence from serial port,
+it stops execution and connects to gdb.
+
 Stubs are not required to recognize these interrupt mechanisms and the
 precise meaning associated with receipt of the interrupt is
 implementation defined.  If the target supports debugging of multiple
diff --git a/gdb/remote.c b/gdb/remote.c
index 43955e9..664a9c7 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -546,14 +546,76 @@ static int remote_async_mask_value = 1;
    this can go away.  */
 static int wait_forever_enabled_p = 1;
 
+/* Allow the user to specify what sequence to send to the remote
+   when he requests a program interruption: Although ^C is usually
+   what remote systems expect (this is the default, here), it is
+   sometimes preferable to send a break.  On other systems such
+   as the Linux kernel, a break followed by g, which is Magic SysRq g
+   is required in order to interrupt the execution.  */
+const char interrupt_sequence_control_c[] = "Ctrl-C";
+const char interrupt_sequence_break[] = "BREAK";
+const char interrupt_sequence_break_g[] = "BREAK-g";
+static const char *interrupt_sequence_modes[] =
+  {
+    interrupt_sequence_control_c,
+    interrupt_sequence_break,
+    interrupt_sequence_break_g,
+    NULL
+  };
+static const char *interrupt_sequence_mode = interrupt_sequence_control_c;
+
+static void
+show_interrupt_sequence (struct ui_file *file, int from_tty,
+			 struct cmd_list_element *c,
+			 const char *value)
+{
+  if (interrupt_sequence_mode == interrupt_sequence_control_c)
+    fprintf_filtered (file,
+		      _("Send the ASCII ETX character (Ctrl-c) "
+			"to the remote target to interrupt the "
+			"execution of the program.\n"));
+  else if (interrupt_sequence_mode == interrupt_sequence_break)
+    fprintf_filtered (file,
+		      _("send a break signal to the remote target "
+			"to interrupt the execution of the program.\n"));
+  else if (interrupt_sequence_mode == interrupt_sequence_break_g)
+    fprintf_filtered (file,
+		      _("Send a break signal and 'g' a.k.a. Magic SysRq g to "
+			"the remote target to interrupt the execution "
+			"of Linux kernel.\n"));
+  else
+    internal_error (__FILE__, __LINE__,
+		    _("Invalid value for interrupt_sequence_mode: %s."),
+		    interrupt_sequence_mode);
+}
 
-/* This variable chooses whether to send a ^C or a break when the user
-   requests program interruption.  Although ^C is usually what remote
-   systems expect, and that is the default here, sometimes a break is
-   preferable instead.  */
+/* This boolean variable specifies whether interrupt_sequence is sent
+   to the remote target when gdb connects to it.
+   This is mostly needed when you debug the Linux kernel: The Linux kernel
+   expects BREAK g which is Magic SysRq g for connecting gdb.  */
+static int interrupt_on_connect = 0;
 
+/* This variable is used to implement the "set/show remotebreak" commands.
+   Since these commands are now deprecated in favor of "set/show remote
+   interrupt-sequence", it no longer has any effect on the code.  */
 static int remote_break;
 
+static void
+set_remotebreak (char *args, int from_tty, struct cmd_list_element *c)
+{
+  if (remote_break)
+    interrupt_sequence_mode = interrupt_sequence_break;
+  else
+    interrupt_sequence_mode = interrupt_sequence_control_c;
+}
+
+static void
+show_remotebreak (struct ui_file *file, int from_tty,
+		  struct cmd_list_element *c,
+		  const char *value)
+{
+}
+
 /* Descriptor for I/O to remote machine.  Initialize it to NULL so that
    remote_open knows that we don't have a file open when the program
    starts.  */
@@ -2604,6 +2666,25 @@ struct start_remote_args
   int extended_p;
 };
 
+/* Send interrupt_sequence to remote target.  */
+static void
+send_interrupt_sequence ()
+{
+  if (interrupt_sequence_mode == interrupt_sequence_control_c)
+    serial_write (remote_desc, "\x03", 1);
+  else if (interrupt_sequence_mode == interrupt_sequence_break)
+    serial_send_break (remote_desc);
+  else if (interrupt_sequence_mode == interrupt_sequence_break_g)
+    {
+      serial_send_break (remote_desc);
+      serial_write (remote_desc, "g", 1);
+    }
+  else
+    internal_error (__FILE__, __LINE__,
+		    _("Invalid value for interrupt_sequence_mode: %s."),
+		    interrupt_sequence_mode);
+}
+
 static void
 remote_start_remote (struct ui_out *uiout, void *opaque)
 {
@@ -2617,6 +2698,9 @@ remote_start_remote (struct ui_out *uiout, void *opaque)
   /* Ack any packet which the remote side has already sent.  */
   serial_write (remote_desc, "+", 1);
 
+  if (interrupt_on_connect)
+    send_interrupt_sequence ();
+
   /* The first packet we send to the target is the optional "supported
      packets" request.  If the target can answer this, it will tell us
      which later probes to skip.  */
@@ -4044,12 +4128,8 @@ remote_stop_as (ptid_t ptid)
   if (rs->cached_wait_status)
     return;
 
-  /* Send a break or a ^C, depending on user preference.  */
-
-  if (remote_break)
-    serial_send_break (remote_desc);
-  else
-    serial_write (remote_desc, "\003", 1);
+  /* Send interrupt_sequence to remote target.  */
+  send_interrupt_sequence ();
 }
 
 /* This is the generic stop called via the target vector. When a target
@@ -9019,6 +9099,8 @@ void
 _initialize_remote (void)
 {
   struct remote_state *rs;
+  struct cmd_list_element *cmd;
+  char *cmd_name;
 
   /* architecture specific data */
   remote_gdbarch_data_handle =
@@ -9086,8 +9168,31 @@ terminating `#' character and checksum."),
 Set whether to send break if interrupted."), _("\
 Show whether to send break if interrupted."), _("\
 If set, a break, instead of a cntrl-c, is sent to the remote target."),
-			   NULL, NULL, /* FIXME: i18n: Whether to send break if interrupted is %s.  */
+			   set_remotebreak, show_remotebreak,
 			   &setlist, &showlist);
+  cmd_name = "remotebreak";
+  cmd = lookup_cmd (&cmd_name, setlist, "", -1, 1);
+  deprecate_cmd (cmd, "set remote interrupt-sequence");
+  cmd_name = "remotebreak"; /* needed because lookup_cmd updates the pointer */
+  cmd = lookup_cmd (&cmd_name, showlist, "", -1, 1);
+  deprecate_cmd (cmd, "show remote interrupt-sequence");
+
+  add_setshow_enum_cmd ("interrupt-sequence", class_support,
+			interrupt_sequence_modes, &interrupt_sequence_mode, _("\
+Set interrupt sequence to remote target."), _("\
+Show interrupt sequence to remote target."), _("\
+Valid value is \"Ctrl-C\", \"BREAK\" or \"BREAK-g\". The default is \"Ctrl-C\"."),
+			NULL, show_interrupt_sequence,
+			&remote_set_cmdlist,
+			&remote_show_cmdlist);
+
+  add_setshow_boolean_cmd ("interrupt-on-connect", class_support,
+			   &interrupt_on_connect, _("\
+Set whether interrupt-sequence is sent to remote target when gdb connects to."), _("		\
+Show whether interrupt-sequence is sent to remote target when gdb connects to."), _("		\
+If set, interrupt sequence is sent to remote target."),
+			   NULL, NULL,
+			   &remote_set_cmdlist, &remote_show_cmdlist);
 
   /* Install commands for configuring memory read/write packets.  */