gdb: add debug prints in event loop

Add debug printouts about event loop-related events:

 - When a file descriptor handler gets invoked
 - When an async event/signal handler gets invoked

gdb/ChangeLog:

	* async-event.c (invoke_async_signal_handlers): Add debug
	print.
	(check_async_event_handlers): Likewise.
	* event-top.c (show_debug_event_loop): New function.
	(_initialize_event_top): Register "set debug event-loop"
	setting.

gdbserver/ChangeLog:

	* server.cc (handle_monitor_command): Handle "set
	debug-event-loop".
	(captured_main): Handle "--debug-event-loop".
	(monitor_show_help): Mention new setting.
	(gdbserver_usage): Mention new flag.

gdbsupport/ChangeLog:

	* event-loop.h (debug_event_loop): New variable declaration.
	(event_loop_debug_printf_1): New function declaration.
	(event_loop_debug_printf): New macro.
	* event-loop.cc (debug_event_loop): New variable.
	(handle_file_event): Add debug print.
	(event_loop_debug_printf_1): New function.

Change-Id: If78ed3a69179881368e7895b42940ce13b6a1a05

2 files changed, 23 insertions, 0 deletions

diff --git a/gdbserver/ChangeLog b/gdbserver/ChangeLog
index 9ed90ba..1f3652b 100644
--- a/gdbserver/ChangeLog
+++ b/gdbserver/ChangeLog
@@ -1,5 +1,13 @@
 2020-10-02  Simon Marchi  <simon.marchi@polymtl.ca>
 
+	* server.cc (handle_monitor_command): Handle "set
+	debug-event-loop".
+	(captured_main): Handle "--debug-event-loop".
+	(monitor_show_help): Mention new setting.
+	(gdbserver_usage): Mention new flag.
+
+2020-10-02  Simon Marchi  <simon.marchi@polymtl.ca>
+
 	* linux-low.cc (linux_process_target::async): Pass name to
 	add_file_handler.
 	* remote-utils.cc (handle_accept_event): Likewise.
diff --git a/gdbserver/server.cc b/gdbserver/server.cc
index d45154d..e6314e5 100644
--- a/gdbserver/server.cc
+++ b/gdbserver/server.cc
@@ -955,6 +955,8 @@ monitor_show_help (void)
   monitor_output ("    Enable h/w breakpoint/watchpoint debugging messages\n");
   monitor_output ("  set remote-debug <0|1>\n");
   monitor_output ("    Enable remote protocol debugging messages\n");
+  monitor_output ("  set event-loop-debug <0|1>\n");
+  monitor_output ("    Enable event loop debugging messages\n");
   monitor_output ("  set debug-format option1[,option2,...]\n");
   monitor_output ("    Add additional information to debugging messages\n");
   monitor_output ("    Options: all, none");
@@ -1389,6 +1391,16 @@ handle_monitor_command (char *mon, char *own_buf)
       remote_debug = 0;
       monitor_output ("Protocol debug output disabled.\n");
     }
+  else if (strcmp (mon, "set event-loop-debug 1") == 0)
+    {
+      debug_event_loop = debug_event_loop_kind::ALL;
+      monitor_output ("Event loop debug output enabled.\n");
+    }
+  else if (strcmp (mon, "set event-loop-debug 0") == 0)
+    {
+      debug_event_loop = debug_event_loop_kind::OFF;
+      monitor_output ("Event loop debug output disabled.\n");
+    }
   else if (startswith (mon, "set debug-format "))
     {
       std::string error_msg
@@ -3468,6 +3480,7 @@ gdbserver_usage (FILE *stream)
 	   "                            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"
@@ -3683,6 +3696,8 @@ captured_main (int argc, char *argv[])
 	}
       else if (strcmp (*next_arg, "--remote-debug") == 0)
 	remote_debug = 1;
+      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)