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

[Andrew Burgess <aburgess@redhat.com>]

Currently, gdbserver has the following command line options related to
debugging output:

  --debug
  --remote-debug
  --event-loop-debug

This doesn't scale well.  If I want an extra debug component we need
to add another command line flag.

This commit changes --debug to take a list of components, I've then
deprecated the --remote-debug and --event-loop-debug options by
removing them from the --help output and man page, and by indicating
that these options are deprecated in the GDB manual.

The currently supported components are: all, threads, remote, and
event-loop.  The 'threads' component represents the debug we currently
get from --debug.  And if --debug is used without a component list
then the threads component is assumed as the default.

Currently the threads component actually includes a lot of output that
is not really threads related.  In the future I'd like to see this
split up and additional components added.

The special component 'all' does what you'd expect: enables debug
output for all supported components.

The component list is parsed left to write, and you can prefix a
component with '-' to disable that component, so I can write:

  target> gdbserver --debug=all,-event-loop

to get debug for all components except the event-loop component.

In this commit I've only update the command line options, in the next
commit I'll update the monitor commands to support a similar
interface.
---
 gdb/NEWS            |   7 ++++
 gdb/doc/gdb.texinfo |  62 +++++++++++++++++++++++----
 gdbserver/server.cc | 100 ++++++++++++++++++++++++++++++++++++++++++--
 3 files changed, 156 insertions(+), 13 deletions(-)

diff --git a/gdb/NEWS b/gdb/NEWS
index 6022def1037..13cf962dfcf 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -6,6 +6,13 @@
 * GDB index now contains information about the main function.  This speeds up
   startup when it is being used for some large binaries.
 
+* New features in the GDB remote stub, GDBserver
+
+  ** The `--debug` option now takes an (optional) list of components
+     to emit debug for.  The currently supported components are all,
+     threads, event-loop, and remote.  This allows the
+     --event-loop-debug and --remote-debug options to be deprecated.
+
 * 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 db1a82ec838..d3f088f6505 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -23664,11 +23664,47 @@
 @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.
+The @option{--debug[=option1,option2,...]} option tells
+@code{gdbserver} to display extra diagnostic information about the
+debugging process.  The @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 relating 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{--remote-debug}, @code{gdbserver} option
-The @option{--remote-debug} option tells @code{gdbserver} to display
-remote protocol debug output.
+The @option{--remote-debug} option is deprecated, but retained for
+backward compatibility.  This is equivalent to
+@option{--debug=remote}.
+
 @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
@@ -50531,16 +50567,24 @@
 target> gdbserver --multi @var{comm}
 @end smallexample
 
-@item --debug
+@item --debug@r{[}=option1,option2,...@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}.
 
 @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 5451d43df18..b954507dd6b 100644
--- a/gdbserver/server.cc
+++ b/gdbserver/server.cc
@@ -1335,6 +1335,66 @@ parse_debug_format_options (const char *arg, int is_monitor)
   return std::string ();
 }
 
+/* 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')
+    {
+      debug_threads = true;
+      return;
+    }
+
+  while (*options != '\0')
+    {
+      const char *end = strchrnul (options, ',');
+
+      bool set_value = *options != '-';
+      if (*options == '-' || *options == '+')
+	++options;
+
+      gdb::string_view opt (options, end - options);
+
+      if (opt.size () == 0)
+	error ("invalid empty debug option");
+
+      bool is_opt_all = opt == "all";
+
+      if (is_opt_all || opt == "threads")
+	debug_threads = set_value;
+      else if (is_opt_all || opt == "event-loop")
+	debug_event_loop = (set_value ? debug_event_loop_kind::ALL
+			    : debug_event_loop_kind::OFF);
+      else if (is_opt_all || opt == "remote")
+	remote_debug = set_value;
+      else
+	error ("unknown debug option '%s'", to_string (opt).c_str ());
+
+      options = (*end == ',') ? end + 1 : end;
+    }
+}
+
 /* Handle monitor commands not handled by target-specific handlers.  */
 
 static void
@@ -3449,15 +3509,19 @@ 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"
@@ -3736,8 +3800,32 @@ 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
@@ -3750,8 +3838,12 @@ captured_main (int argc, char *argv[])
 	      exit (1);
 	    }
 	}
+      /* This option is retained for backwards compatibility.  It is
+	 considered deprecated, and might be removed one day.  */
       else if (strcmp (*next_arg, "--remote-debug") == 0)
 	remote_debug = true;
+      /* This option is retained for backwards compatibility.  It is
+	 considered deprecated, and might be removed one day.  */
       else if (strcmp (*next_arg, "--event-loop-debug") == 0)
 	debug_event_loop = debug_event_loop_kind::ALL;
       else if (startswith (*next_arg, "--debug-file="))
-- 
2.25.4