New vCtrlC packet, non-stop mode equivalent of \003

There's currently no non-stop equivalent of the all-stop ^C (\003)
"packet" that GDB sends when a ctrl-c is pressed while a foreground
command is active.  There's vCont;t, but that's defined to cause a
"signal 0" stop.

This fixes many tests that type ^C, when testing with extended-remote
with "maint set target-non-stop on".  E.g.:

 Continuing.
 talk to me baby
 PASS: gdb.base/interrupt.exp: process is alive
 a
 a
 PASS: gdb.base/interrupt.exp: child process ate our char
 ^C
 [Thread 22730.22730] #1 stopped.
 0x0000003615ee6650 in __read_nocancel () at ../sysdeps/unix/syscall-template.S:81
 81      T_PSEUDO (SYSCALL_SYMBOL, SYSCALL_NAME, SYSCALL_NARGS)
 (gdb) FAIL: gdb.base/interrupt.exp: send_gdb control C
 p func1 ()

gdb/
2015-10-14  Pedro Alves  <palves@redhat.com>

	* NEWS (New remote packets): Mention vCtrlC.

gdb/doc/
2015-10-14  Pedro Alves  <palves@redhat.com>

	* gdb.texinfo (Bootstrapping): Add
	"interrupting remote targets" anchor.
	(Packets): Document vCtrlC.

gdb/gdbserver/
2015-10-14  Pedro Alves  <palves@redhat.com>

	* server.c (handle_v_requests): Handle vCtrlC.
	* remote.c (PACKET_vCtrlC): New enum value.
	(async_remote_interrupt): Call target_interrupt instead of
	target_stop.
	(remote_interrupt_as): Remove 'ptid' parameter.
	(remote_interrupt_ns): New function.
	(remote_stop): Adjust.
	(remote_interrupt): If the target is in non-stop mode, try
	interrupting with vCtrlC.
	(initialize_remote): Install set remote ctrl-c packet.

4 files changed, 98 insertions, 11 deletions

diff --git a/gdb/NEWS b/gdb/NEWS
index 2e38d9a6c8d..84c75cc7723 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -75,6 +75,10 @@ exec-events feature in qSupported
   response can contain the corresponding 'stubfeature'.  Set and
   show commands can be used to display whether these features are enabled.
 
+vCtrlC
+  Equivalent to interrupting with the ^C character, but works in
+  non-stop mode.
+
 * Extended-remote exec events
 
   ** GDB now has support for exec events on extended-remote Linux targets.
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index f298172da27..196a842dbac 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -35087,6 +35087,24 @@ command in the @samp{vCont} packet.
 The @samp{vCont} packet is not supported.
 @end table
 
+@anchor{vCtrlC packet}
+@item vCtrlC
+@cindex @samp{vCtrlC} packet
+Interrupt remote target as if a control-C was pressed on the remote
+terminal.  This is the equivalent to reacting to the @code{^C}
+(@samp{\003}, the control-C character) character in all-stop mode
+while the target is running, except this works in non-stop mode.
+@xref{interrupting remote targets}, for more info on the all-stop
+variant.
+
+Reply:
+@table @samp
+@item E @var{nn}
+for an error
+@item OK
+for success
+@end table
+
 @item vFile:@var{operation}:@var{parameter}@dots{}
 @cindex @samp{vFile} packet
 Perform a file operation on the target system.  For details,
@@ -37854,11 +37872,12 @@ operation.
 @node Interrupts
 @section Interrupts
 @cindex interrupts (remote protocol)
+@anchor{interrupting remote targets}
 
-When a program on the remote target is running, @value{GDBN} may
-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}.
+In all-stop mode, when a program on the remote target is running,
+@value{GDBN} may 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
@@ -37879,6 +37898,13 @@ and does @emph{not} represent an interrupt.  E.g., an @samp{X} packet
 When Linux kernel receives this sequence from serial port,
 it stops execution and connects to gdb.
 
+In non-stop mode, because packet resumptions are asynchronous
+(@pxref{vCont packet}), @value{GDBN} is always free to send a remote
+command to the remote stub, even when the target is running.  For that
+reason, @value{GDBN} instead sends a regular packet (@pxref{vCtrlC
+packet}) with the usual packet framing instead of the single byte
+@code{0x03}.
+
 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/gdbserver/server.c b/gdb/gdbserver/server.c
index ec52f841c8c..e0ce524ec5c 100644
--- a/gdb/gdbserver/server.c
+++ b/gdb/gdbserver/server.c
@@ -2849,6 +2849,13 @@ handle_v_requests (char *own_buf, int packet_len, int *new_packet_len)
 {
   if (!disable_packet_vCont)
     {
+      if (strcmp (own_buf, "vCtrlC") == 0)
+	{
+	  (*the_target->request_interrupt) ();
+	  write_ok (own_buf);
+	  return;
+	}
+
       if (startswith (own_buf, "vCont;"))
 	{
 	  require_running (own_buf);
diff --git a/gdb/remote.c b/gdb/remote.c
index 10c65e2fcce..9a23ca6e6c0 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -1478,6 +1478,9 @@ enum {
   /* Support for query supported vCont actions.  */
   PACKET_vContSupported,
 
+  /* Support remote CTRL-C.  */
+  PACKET_vCtrlC,
+
   PACKET_MAX
 };
 
@@ -5553,7 +5556,7 @@ async_remote_interrupt (gdb_client_data arg)
   if (remote_debug)
     fprintf_unfiltered (gdb_stdlog, "async_remote_interrupt called\n");
 
-  target_stop (inferior_ptid);
+  target_interrupt (inferior_ptid);
 }
 
 /* Perform interrupt, if the first attempt did not succeed.  Just give
@@ -5660,7 +5663,7 @@ remote_stop_ns (ptid_t ptid)
    process reports the interrupt.  */
 
 static void
-remote_interrupt_as (ptid_t ptid)
+remote_interrupt_as (void)
 {
   struct remote_state *rs = get_remote_state ();
 
@@ -5676,6 +5679,37 @@ remote_interrupt_as (ptid_t ptid)
   send_interrupt_sequence ();
 }
 
+/* Non-stop version of target_interrupt.  Uses `vCtrlC' to interrupt
+   the remote target.  It is undefined which thread of which process
+   reports the interrupt.  */
+
+static int
+remote_interrupt_ns (void)
+{
+  struct remote_state *rs = get_remote_state ();
+  char *p = rs->buf;
+  char *endp = rs->buf + get_remote_packet_size ();
+
+  xsnprintf (p, endp - p, "vCtrlC");
+
+  /* In non-stop, we get an immediate OK reply.  The stop reply will
+     come in asynchronously by notification.  */
+  putpkt (rs->buf);
+  getpkt (&rs->buf, &rs->buf_size, 0);
+
+  switch (packet_ok (rs->buf, &remote_protocol_packets[PACKET_vCtrlC]))
+    {
+    case PACKET_OK:
+      break;
+    case PACKET_UNKNOWN:
+      return 0;
+    case PACKET_ERROR:
+      error (_("Interrupting target failed: %s"), rs->buf);
+    }
+
+  return 1;
+}
+
 /* Implement the to_stop function for the remote targets.  */
 
 static void
@@ -5690,7 +5724,7 @@ remote_stop (struct target_ops *self, ptid_t ptid)
     {
       /* We don't currently have a way to transparently pause the
 	 remote target in all-stop mode.  Interrupt it instead.  */
-      remote_interrupt_as (ptid);
+      remote_interrupt_as ();
     }
 }
 
@@ -5702,14 +5736,27 @@ remote_interrupt (struct target_ops *self, ptid_t ptid)
   if (remote_debug)
     fprintf_unfiltered (gdb_stdlog, "remote_interrupt called\n");
 
-  if (target_is_non_stop_p ())
+  if (non_stop)
     {
-      /* We don't currently have a way to ^C the remote target in
-	 non-stop mode.  Stop it (with no signal) instead.  */
+      /* In non-stop mode, we always stop with no signal instead.  */
       remote_stop_ns (ptid);
     }
   else
-    remote_interrupt_as (ptid);
+    {
+      /* In all-stop, we emulate ^C-ing the remote target's
+	 terminal.  */
+      if (target_is_non_stop_p ())
+	{
+	  if (!remote_interrupt_ns ())
+	    {
+	      /* No support for ^C-ing the remote target.  Stop it
+		 (with no signal) instead.  */
+	      remote_stop_ns (ptid);
+	    }
+	}
+      else
+	remote_interrupt_as ();
+    }
 }
 
 /* Ask the user what to do when an interrupt is received.  */
@@ -13612,6 +13659,9 @@ Show the maximum size of the address (in bits) in a memory packet."), NULL,
   add_packet_config_cmd (&remote_protocol_packets[PACKET_exec_event_feature],
 			 "exec-event-feature", "exec-event-feature", 0);
 
+  add_packet_config_cmd (&remote_protocol_packets[PACKET_vCtrlC],
+			 "vCtrlC", "ctrl-c", 0);
+
   /* Assert that we've registered "set remote foo-packet" commands
      for all packet configs.  */
   {