[PATCHv2,2/3] gdbserver: allow the --debug command line option to take a value

diff --git a/gdb/NEWS b/gdb/NEWS
index 1073e38dfc6..94d1fd8ea8d 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -38,6 +38,16 @@  set remote thread-options-packet
 show remote thread-options-packet
   Set/show the use of the thread options packet.
 
+* New features in the GDB remote stub, GDBserver
+
+  ** The --remote-debug and --event-loop-debug command line options
+     have been removed.
+
+  ** The --debug command line option now takes an optional comma
+     separated list of components to emit debug for.  The currently
+     supported components are: all, threads, event-loop, and remote.
+     If no components are given then threads is assumed.
+
 * Python API
 
   ** New function gdb.notify_mi(NAME, DATA), that emits custom
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index e4c00143fd1..9e46eba4ac9 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -23674,11 +23674,42 @@ 
 @pxref{--multi Option in Types of Remote Connnections}.
 
 @cindex @option{--debug}, @code{gdbserver} option
-The @option{--debug} option tells @code{gdbserver} to display extra
-status information about the debugging process.
-@cindex @option{--remote-debug}, @code{gdbserver} option
-The @option{--remote-debug} option tells @code{gdbserver} to display
-remote protocol debug output.
+The @option{--debug[=option1,option2,@dots{}]} option tells
+@code{gdbserver} to display extra diagnostic information about the
+debugging process.  The options (@var{option1}, @var{option2}, etc)
+control for which areas of @code{gdbserver} additional information
+will be displayed, possible values are:
+
+@table @code
+@item all
+This enables all available diagnostic output.
+@item threads
+This enables diagnostic output related to threading.  Currently other
+general diagnostic output is included in this category, but this could
+change in future releases of @code{gdbserver}.
+@item event-loop
+This enables event-loop specific diagnostic output.
+@item remote
+This enables diagnostic output related to the transfer of remote
+protocol packets too and from the debugger.
+@end table
+
+@noindent
+If no options are passed to @option{--debug} then this is treated as
+equivalent to @option{--debug=threads}.  This could change in future
+releases of @code{gdbserver}.  The options passed to @option{--debug}
+are processed left to right, and individual options can be prefixed
+with the @kbd{-} (minus) character to disable diagnostic output from
+this area, so it is possible to use:
+
+@smallexample
+  target> gdbserver --debug=all,-event-loop
+@end smallexample
+
+@noindent
+In order to enable all diagnostic output except that for the
+event-loop.
+
 @cindex @option{--debug-file}, @code{gdbserver} option
 @cindex @code{gdbserver}, send all debug output to a single file
 The @option{--debug-file=@var{filename}} option tells @code{gdbserver} to
@@ -50667,16 +50698,27 @@ 
 target> gdbserver --multi @var{comm}
 @end smallexample
 
-@item --debug
-Instruct @code{gdbserver} to display extra status information about the debugging
-process.
-This option is intended for @code{gdbserver} development and for bug reports to
-the developers.
+@item --debug@r{[}=option1,option2,@dots{}@r{]}
+Instruct @code{gdbserver} to display extra status information about
+the debugging process.  This option is intended for @code{gdbserver}
+development and for bug reports to the developers.
 
-@item --remote-debug
-Instruct @code{gdbserver} to display remote protocol debug output.
-This option is intended for @code{gdbserver} development and for bug reports to
-the developers.
+Each @var{option} is the name of a component for which debugging
+should be enabled.  The list of possible options is @option{all},
+@option{threads}, @option{event-loop}, @option{remote}.  The special
+option @option{all} enables all components.  The option list is
+processed left to right, and an option can be prefixed with the
+@kbd{-} character to disable output for that component, so you could write:
+
+@smallexample
+target> gdbserver --debug=all,-event-loop
+@end smallexample
+
+@noindent
+to turn on debug output for all components except @option{event-loop}.
+If no options are passed to @option{--debug} then this is treated as
+equivalent to @option{--debug=threads}.  This could change in future
+releases of @code{gdbserver}.
 
 @item --debug-file=@var{filename}
 Instruct @code{gdbserver} to send any debug output to the given @var{filename}.
diff --git a/gdbserver/server.cc b/gdbserver/server.cc
index f91f70d2aa9..3cb71a861d5 100644
--- a/gdbserver/server.cc
+++ b/gdbserver/server.cc
@@ -1457,6 +1457,124 @@  parse_debug_format_options (const char *arg, int is_monitor)
   return std::string ();
 }
 
+/* A wrapper to enable, or disable a debug flag.  These are debug flags
+   that control the debug output from gdbserver, that developers might
+   want, this is not something most end users will need.  */
+
+struct debug_opt
+{
+  /* NAME is the name of this debug option, this should be a simple string
+     containing no whitespace, starting with a letter from isalpha(), and
+     contain only isalnum() characters and '_' underscore and '-' hyphen.
+
+     SETTER is a callback function used to set the debug variable.  This
+     callback will be passed true to enable the debug setting, or false to
+     disable the debug setting.  */
+  debug_opt (const char *name, std::function<void (bool)> setter)
+    : m_name (name),
+      m_setter (setter)
+  {
+    gdb_assert (isalpha (*name));
+  }
+
+  /* Called to enable or disable the debug setting.  */
+  void set (bool enable) const
+  {
+    m_setter (enable);
+  }
+
+  /* Return the name of this debug option.  */
+  const char *name () const
+  { return m_name; }
+
+private:
+  /* The name of this debug option.  */
+  const char *m_name;
+
+  /* The callback to update the debug setting.  */
+  std::function<void (bool)> m_setter;
+};
+
+/* The set of all debug options that gdbserver supports.  These are the
+   options that can be passed to the command line '--debug=...' flag, or to
+   the monitor command 'monitor set debug ...'.  */
+
+static std::vector<debug_opt> all_debug_opt {
+  {"threads", [] (bool enable)
+  {
+    debug_threads = enable;
+  }},
+  {"remote", [] (bool enable)
+  {
+    remote_debug = enable;
+  }},
+  {"event-loop", [] (bool enable)
+  {
+    debug_event_loop = (enable ? debug_event_loop_kind::ALL
+			: debug_event_loop_kind::OFF);
+  }}
+};
+
+/* Parse the options to --debug=...
+
+   OPTIONS is the string of debug components which should be enabled (or
+   disabled), and must not be nullptr.  An empty OPTIONS string is valid,
+   in which case a default set of debug components will be enabled.
+
+   An unknown, or otherwise invalid debug component will result in an
+   exception being thrown.
+
+   OPTIONS can consist of multiple debug component names separated by a
+   comma.  Debugging for each component will be turned on.  The special
+   component 'all' can be used to enable debugging for all components.
+
+   A component can also be prefixed with '-' to disable debugging of that
+   component, so a user might use: '--debug=all,-remote', to enable all
+   debugging, except for the remote (protocol) component.  Components are
+   processed left to write in the OPTIONS list.  */
+
+static void
+parse_debug_options (const char *options)
+{
+  gdb_assert (options != nullptr);
+
+  /* Empty options means the "default" set.  This exists mostly for
+     backwards compatibility with gdbserver's legacy behaviour.  */
+  if (*options == '\0')
+    options = "+threads";
+
+  while (*options != '\0')
+    {
+      const char *end = strchrnul (options, ',');
+
+      bool enable = *options != '-';
+      if (*options == '-' || *options == '+')
+	++options;
+
+      std::string opt (options, end - options);
+
+      if (opt.size () == 0)
+	error ("invalid empty debug option");
+
+      bool is_opt_all = opt == "all";
+
+      bool found = false;
+      for (const auto &debug_opt : all_debug_opt)
+	if (is_opt_all || opt == debug_opt.name ())
+	  {
+	    debug_opt.set (enable);
+	    found = true;
+	    if (!is_opt_all)
+	      break;
+	  }
+
+      if (!found)
+	error ("unknown debug option '%s'", opt.c_str ());
+
+      options = (*end == ',') ? end + 1 : end;
+    }
+}
+
 /* Handle monitor commands not handled by target-specific handlers.  */
 
 static void
@@ -3583,15 +3701,19 @@  gdbserver_usage (FILE *stream)
 	   "\n"
 	   "Debug options:\n"
 	   "\n"
-	   "  --debug               Enable general debugging output.\n"
+	   "  --debug[=OPT1,OPT2,...]\n"
+	   "                        Enable debugging output.\n"
+	   "                          Options:\n"
+	   "                            all, threads, event-loop, remote\n"
+	   "                          With no options, 'threads' is assumed.\n"
+	   "                          Prefix an option with '-' to disable\n"
+	   "                          debugging of that component.\n"
 	   "  --debug-format=OPT1[,OPT2,...]\n"
 	   "                        Specify extra content in debugging output.\n"
 	   "                          Options:\n"
 	   "                            all\n"
 	   "                            none\n"
 	   "                            timestamp\n"
-	   "  --remote-debug        Enable remote protocol debugging output.\n"
-	   "  --event-loop-debug    Enable event loop debugging output.\n"
 	   "  --disable-packet=OPT1[,OPT2,...]\n"
 	   "                        Disable support for RSP packets or features.\n"
 	   "                          Options:\n"
@@ -3870,8 +3992,32 @@  captured_main (int argc, char *argv[])
 	  /* Consume the "--".  */
 	  *next_arg = NULL;
 	}
+      else if (startswith (*next_arg, "--debug="))
+	{
+	  try
+	    {
+	      parse_debug_options ((*next_arg) + sizeof ("--debug=") - 1);
+	    }
+	  catch (const gdb_exception_error &exception)
+	    {
+	      fflush (stdout);
+	      fprintf (stderr, "gdbserver: %s\n", exception.what ());
+	      exit (1);
+	    }
+	}
       else if (strcmp (*next_arg, "--debug") == 0)
-	debug_threads = true;
+	{
+	  try
+	    {
+	      parse_debug_options ("");
+	    }
+	  catch (const gdb_exception_error &exception)
+	    {
+	      fflush (stdout);
+	      fprintf (stderr, "gdbserver: %s\n", exception.what ());
+	      exit (1);
+	    }
+	}
       else if (startswith (*next_arg, "--debug-format="))
 	{
 	  std::string error_msg
@@ -3884,10 +4030,6 @@  captured_main (int argc, char *argv[])
 	      exit (1);
 	    }
 	}
-      else if (strcmp (*next_arg, "--remote-debug") == 0)
-	remote_debug = true;
-      else if (strcmp (*next_arg, "--event-loop-debug") == 0)
-	debug_event_loop = debug_event_loop_kind::ALL;
       else if (startswith (*next_arg, "--debug-file="))
 	debug_set_output ((*next_arg) + sizeof ("--debug-file=") -1);
       else if (strcmp (*next_arg, "--disable-packet") == 0)