Implement TARGET_WAITKIND_NO_RESUMED in the remote protocol

Testing with "maint set target-non-stop on" causes regressions in
tests that rely on TARGET_WAITKIND_NO_RESUMED, which isn't modelled on
the RSP.  In real all-stop, gdbserver detects the situation and
reporst error to GDB, and so the tests (e.g.,
gdb.threads/no-unwaited-for-left.exp) at fail quickly.  But with
"maint set target-non-stop on", GDB instead hangs forever waiting for
a stop reply that never comes, and so the tests take longer to time
out.

This adds a new "N" stop reply packet that maps 1-1 to
TARGET_WAITKIND_NO_RESUMED.

gdb/ChangeLog:
2015-11-30  Pedro Alves  <palves@redhat.com>

	PR 14618
	* NEWS (New remote packets): Mention the N stop reply.
	* remote.c (remote_protocol_features): Add "no-resumed" entry.
	(remote_query_supported): Report no-resumed+ support.
	(remote_parse_stop_reply): Handle 'N'.
	(process_stop_reply): Handle TARGET_WAITKIND_NO_RESUMED.
	(remote_wait_as): Handle 'N' / TARGET_WAITKIND_NO_RESUMED.
	(_initialize_remote): Register "set/show remote
	no-resumed-stop-reply" commands.

gdb/doc/ChangeLog:
2015-11-30  Pedro Alves  <palves@redhat.com>

	PR 14618
	* gdb.texinfo (Stop Reply Packets): Document the N stop reply.
	(Remote Configuration): Add the "set/show remote
	no-resumed-stop-reply" to the available settings table.
	(General Query Packets): Document the "no-resumed" qSupported
	feature.

gdb/gdbserver/ChangeLog:
2015-11-30  Pedro Alves  <palves@redhat.com>

	PR 14618
	* linux-low.c (linux_wait_1): If the last resumed thread is gone,
	report TARGET_WAITKIND_NO_RESUMED.
	* remote-utils.c (prepare_resume_reply): Handle
	TARGET_WAITKIND_NO_RESUMED.
	* server.c (report_no_resumed): New global.
	(handle_query) <qSupported>: Handle "no-resumed+".  Report
	"no-resumed+" support.
	(resume): When the target reports TARGET_WAITKIND_NO_RESUMED, only
	return error if the client doesn't support no-resumed events.
	(push_stop_notification): New function.
	(handle_target_event): Use it.  Report TARGET_WAITKIND_NO_RESUMED
	events if the client supports them.

gdb/testsuite/ChangeLog:
2015-11-30  Pedro Alves  <palves@redhat.com>

	* gdb.threads/no-unwaited-for-left.exp: Remove setup_kfail calls.

2 files changed, 36 insertions, 0 deletions

diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog
index b5eddc9..2c58ffe 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,5 +1,14 @@
 2015-11-30  Pedro Alves  <palves@redhat.com>
 
+	PR 14618
+	* gdb.texinfo (Stop Reply Packets): Document the N stop reply.
+	(Remote Configuration): Add the "set/show remote
+	no-resumed-stop-reply" to the available settings table.
+	(General Query Packets): Document the "no-resumed" qSupported
+	feature.
+
+2015-11-30  Pedro Alves  <palves@redhat.com>
+
 	* gdb.texinfo (Remote Configuration): List "set/show remote
 	thread-events" command in configuration table.
 	(Stop Reply Packets): Document "T05 create" stop
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index d2ec354..b82f3c6 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -20239,6 +20239,10 @@ are:
 @tab @code{QThreadEvents}
 @tab Tracking thread lifetime.
 
+@item @code{no-resumed-stop-reply}
+@tab @code{no resumed thread left stop reply}
+@tab Tracking thread lifetime.
+
 @end multitable
 
 @node Remote Stub
@@ -35588,6 +35592,21 @@ The thread exited, and @var{AA} is the exit status.  This response
 should not be sent by default; @value{GDBN} requests it with the
 @ref{QThreadEvents} packet.  See also @ref{thread create event} above.
 
+@item N
+There are no resumed threads left in the target.  In other words, even
+though the process is alive, the last resumed thread has exited.  For
+example, say the target process has two threads: thread 1 and thread
+2.  The client leaves thread 1 stopped, and resumes thread 2, which
+subsequently exits.  At this point, even though the process is still
+alive, and thus no @samp{W} stop reply is sent, no thread is actually
+executing either.  The @samp{N} stop reply thus informs the client
+that it can stop waiting for stop replies.  This packet should not be
+sent by default; older @value{GDBN} versions did not support it.
+@value{GDBN} requests it, by supplying an appropriate
+@samp{qSupported} feature (@pxref{qSupported}).  The remote stub must
+also supply the appropriate @samp{qSupported} feature indicating
+support.
+
 @item O @var{XX}@dots{}
 @samp{@var{XX}@dots{}} is hex encoding of @sc{ascii} data, to be
 written as the program's console output.  This can happen at any time
@@ -36487,6 +36506,11 @@ These are the currently defined stub features and their properties:
 @tab @samp{-}
 @tab No
 
+@item @samp{no-resumed}
+@tab No
+@tab @samp{-}
+@tab No
+
 @end multitable
 
 These are the currently defined stub features, in more detail:
@@ -36702,6 +36726,9 @@ The remote stub reports the supported actions in the reply to
 @item QThreadEvents
 The remote stub understands the @samp{QThreadEvents} packet.
 
+@item no-resumed
+The remote stub reports the @samp{N} stop reply.
+
 @end table
 
 @item qSymbol::