Fix "breakpoint always-inserted off"; remove "breakpoint always-inserted auto"

By default, GDB removes all breakpoints from the target when the
target stops and the prompt is given back to the user.  This is useful
in case GDB crashes while the user is interacting, as otherwise,
there's a higher chance breakpoints would be left planted on the
target.

But, as long as any thread is running free, we need to make sure to
keep breakpoints inserted, lest a thread misses a breakpoint.  With
that in mind, in preparation for non-stop mode, we added a "breakpoint
always-inserted on" mode.  This traded off the extra crash protection
for never having threads miss breakpoints, and in addition is more
efficient if there's a ton of breakpoints to remove/insert at each
user command (e.g., at each "step").

When we added non-stop mode, and for a period, we required users to
manually set "always-inserted on" when they enabled non-stop mode, as
otherwise GDB removes all breakpoints from the target as soon as any
thread stops, which means the other threads still running will miss
breakpoints.  The test added by this patch exercises this.

That soon revealed a nuisance, and so later we added an extra
"breakpoint always-inserted auto" mode, that made GDB behave like
"always-inserted on" when non-stop was enabled, and "always-inserted
off" when non-stop was disabled.  "auto" was made the default at the
same time.

In hindsight, this "auto" setting was unnecessary, and not the ideal
solution.  Non-stop mode does depends on breakpoints always-inserted
mode, but only as long as any thread is running.  If no thread is
running, no breakpoint can be missed.  The same is true for all-stop
too.  E.g., if, in all-stop mode, and the user does:

 (gdb) c&
 (gdb) b foo

That breakpoint at "foo" should be inserted immediately, but it
currently isn't -- currently it'll end up inserted only if the target
happens to trip on some event, and is re-resumed, e.g., an internal
breakpoint triggers that doesn't cause a user-visible stop, and so we
end up in keep_going calling insert_breakpoints.  The test added by
this patch also covers this.

IOW, no matter whether in non-stop or all-stop, if the target fully
stops, we can remove breakpoints.  And no matter whether in all-stop
or non-stop, if any thread is running in the target, then we need
breakpoints to be immediately inserted.  And then, if the target has
global breakpoints, we need to keep breakpoints even when the target
is stopped.

So with that in mind, and aiming at reducing all-stop vs non-stop
differences for all-stop-on-stop-of-non-stop, this patch fixes
"breakpoint always-inserted off" to not remove breakpoints from the
target until it fully stops, and then removes the "auto" setting as
unnecessary.  I propose removing it straight away rather than keeping
it as an alias, unless someone complains they have scripts that need
it and that can't adjust.

Tested on x86_64 Fedora 20.

gdb/
2014-09-22  Pedro Alves  <palves@redhat.com>

	* NEWS: Mention merge of "breakpoint always-inserted" modes "off"
	and "auto" merged.
	* breakpoint.c (enum ugll_insert_mode): New enum.
	(always_inserted_mode): Now a plain boolean.
	(show_always_inserted_mode): No longer handle AUTO_BOOLEAN_AUTO.
	(breakpoints_always_inserted_mode): Delete.
	(breakpoints_should_be_inserted_now): New function.
	(insert_breakpoints): Pass UGLL_INSERT to
	update_global_location_list instead of calling
	insert_breakpoint_locations manually.
	(create_solib_event_breakpoint_1): New, factored out from ...
	(create_solib_event_breakpoint): ... this.
	(create_and_insert_solib_event_breakpoint): Use
	create_solib_event_breakpoint_1 instead of calling
	insert_breakpoint_locations manually.
	(update_global_location_list): Change parameter type from boolean
	to enum ugll_insert_mode.  All callers adjusted.  Adjust to use
	breakpoints_should_be_inserted_now and handle UGLL_INSERT.
	(update_global_location_list_nothrow): Change parameter type from
	boolean to enum ugll_insert_mode.
	(_initialize_breakpoint): "breakpoint always-inserted" option is
	now a boolean command.  Update help text.
	* breakpoint.h (breakpoints_always_inserted_mode): Delete declaration.
	(breakpoints_should_be_inserted_now): New declaration.
	* infrun.c (handle_inferior_event) <TARGET_WAITKIND_LOADED>:
	Remove breakpoints_always_inserted_mode check.
	(normal_stop): Adjust to use breakpoints_should_be_inserted_now.
	* remote.c (remote_start_remote): Likewise.

gdb/doc/
2014-09-22  Pedro Alves  <palves@redhat.com>

	* gdb.texinfo (Set Breaks): Document that "set breakpoint
	always-inserted off" is the default mode now.  Delete
	documentation of "set breakpoint always-inserted auto".

gdb/testsuite/
2014-09-22  Pedro Alves  <palves@redhat.com>

	* gdb.threads/break-while-running.exp: New file.
	* gdb.threads/break-while-running.c: New file.

1 files changed, 53 insertions, 37 deletions

diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index 3f372de..3675b4f 100644
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -258,12 +258,17 @@ enum ugll_insert_mode
      the inferior.  */
   UGLL_DONT_INSERT,
 
-  /* May insert breakpoints if breakpoints_always_inserted_mode is
-     true.  */
+  /* May insert breakpoints iff breakpoints_should_be_inserted_now
+     claims breakpoints should be inserted now.  */
   UGLL_MAY_INSERT,
 
-  /* Insert locations now, even if breakpoints_always_inserted_mode is
-     false.  */
+  /* Insert locations now, irrespective of
+     breakpoints_should_be_inserted_now.  E.g., say all threads are
+     stopped right now, and the user did "continue".  We need to
+     insert breakpoints _before_ resuming the target, but
+     UGLL_MAY_INSERT wouldn't insert them, because
+     breakpoints_should_be_inserted_now returns false at that point,
+     as no thread is running yet.  */
   UGLL_INSERT
 };
 
@@ -451,34 +456,51 @@ show_automatic_hardware_breakpoints (struct ui_file *file, int from_tty,
 		    value);
 }
 
-/* If on, gdb will keep breakpoints inserted even as inferior is
-   stopped, and immediately insert any new breakpoints.  If off, gdb
-   will insert breakpoints into inferior only when resuming it, and
-   will remove breakpoints upon stop.  If auto, GDB will behave as ON
-   if in non-stop mode, and as OFF if all-stop mode.*/
-
-static enum auto_boolean always_inserted_mode = AUTO_BOOLEAN_AUTO;
+/* If on, GDB keeps breakpoints inserted even if the inferior is
+   stopped, and immediately inserts any new breakpoints as soon as
+   they're created.  If off (default), GDB keeps breakpoints off of
+   the target as long as possible.  That is, it delays inserting
+   breakpoints until the next resume, and removes them again when the
+   target fully stops.  This is a bit safer in case GDB crashes while
+   processing user input.  */
+static int always_inserted_mode = 0;
 
 static void
 show_always_inserted_mode (struct ui_file *file, int from_tty,
 		     struct cmd_list_element *c, const char *value)
 {
-  if (always_inserted_mode == AUTO_BOOLEAN_AUTO)
-    fprintf_filtered (file,
-		      _("Always inserted breakpoint "
-			"mode is %s (currently %s).\n"),
-		      value,
-		      breakpoints_always_inserted_mode () ? "on" : "off");
-  else
-    fprintf_filtered (file, _("Always inserted breakpoint mode is %s.\n"),
-		      value);
+  fprintf_filtered (file, _("Always inserted breakpoint mode is %s.\n"),
+		    value);
 }
 
 int
-breakpoints_always_inserted_mode (void)
+breakpoints_should_be_inserted_now (void)
 {
-  return (always_inserted_mode == AUTO_BOOLEAN_TRUE
-	  || (always_inserted_mode == AUTO_BOOLEAN_AUTO && non_stop));
+  if (gdbarch_has_global_breakpoints (target_gdbarch ()))
+    {
+      /* If breakpoints are global, they should be inserted even if no
+	 thread under gdb's control is running, or even if there are
+	 no threads under GDB's control yet.  */
+      return 1;
+    }
+  else if (target_has_execution)
+    {
+      struct thread_info *tp;
+
+      if (always_inserted_mode)
+	{
+	  /* The user wants breakpoints inserted even if all threads
+	     are stopped.  */
+	  return 1;
+	}
+
+      ALL_NON_EXITED_THREADS (tp)
+        {
+	  if (tp->executing)
+	    return 1;
+	}
+    }
+  return 0;
 }
 
 static const char condition_evaluation_both[] = "host or target";
@@ -12930,10 +12952,7 @@ update_global_location_list (enum ugll_insert_mode insert_mode)
 			"a permanent breakpoint"));
     }
 
-  if (insert_mode == UGLL_INSERT
-      || (breakpoints_always_inserted_mode ()
-	  && (have_live_inferiors ()
-	      || (gdbarch_has_global_breakpoints (target_gdbarch ())))))
+  if (insert_mode == UGLL_INSERT || breakpoints_should_be_inserted_now ())
     {
       if (insert_mode != UGLL_DONT_INSERT)
 	insert_breakpoint_locations ();
@@ -17020,18 +17039,15 @@ a warning will be emitted for such breakpoints."),
 			   &breakpoint_set_cmdlist,
 			   &breakpoint_show_cmdlist);
 
-  add_setshow_auto_boolean_cmd ("always-inserted", class_support,
-				&always_inserted_mode, _("\
+  add_setshow_boolean_cmd ("always-inserted", class_support,
+			   &always_inserted_mode, _("\
 Set mode for inserting breakpoints."), _("\
 Show mode for inserting breakpoints."), _("\
-When this mode is off, breakpoints are inserted in inferior when it is\n\
-resumed, and removed when execution stops.  When this mode is on,\n\
-breakpoints are inserted immediately and removed only when the user\n\
-deletes the breakpoint.  When this mode is auto (which is the default),\n\
-the behaviour depends on the non-stop setting (see help set non-stop).\n\
-In this case, if gdb is controlling the inferior in non-stop mode, gdb\n\
-behaves as if always-inserted mode is on; if gdb is controlling the\n\
-inferior in all-stop mode, gdb behaves as if always-inserted mode is off."),
+When this mode is on, breakpoints are inserted immediately as soon as\n\
+they're created, kept inserted even when execution stops, and removed\n\
+only when the user deletes them.  When this mode is off (the default),\n\
+breakpoints are inserted only when execution continues, and removed\n\
+when execution stops."),
 				NULL,
 				&show_always_inserted_mode,
 				&breakpoint_set_cmdlist,