[PATCH v3 3/3] Fix "breakpoint always-inserted off"; remove "breakpoint always-inserted auto"

[Pedro Alves <palves at redhat dot com>]

On 09/18/2014 02:45 AM, Yao Qi wrote:
> Pedro Alves <palves@redhat.com> writes:
> 
>> -  /* 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
> 
> Yeah, that is clear to me.

Good.  :-)

>> +   You should have received a copy of the GNU General Public License
>> +   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
>> +
>> +#include <pthread.h>
>> +#include <assert.h>
>> +#include <pthread.h>
> 
> pthread.h is included twice.

Thanks, fixed.

>> +
>> +    gdb_breakpoint [gdb_get_line_number "breakpoint A child here"]
>> +    gdb_continue_to_breakpoint "run to child breakpoint"
>> +    gdb_test "info threads" "\\\* 2 .* 1.*" "info threads shows all threads"
>> +
>> +    delete_breakpoints
>> +
>> +    # Leave one thread stopped, so GDB
>> +    gdb_test_no_output "set scheduler-locking on"
>> +
>> +    gdb_test "continue &" "Continuing\."
>> +
>> +    # Switch to a stopped thread, so GDB can poke at memory freely.
>> +    gdb_test "thread 1" "Switching to .*" "switch to stopped thread"
>> +
>> +    gdb_test "info threads" "2.*running.*\\\* 1.*" "info threads shows running thread"
>> +
> 
> IWBN to check thread 1 is stopped too, because thread 1 isn't stopped in
> non-stop mode, or the test can stop thread 1 explicitly if it isn't.

The test actually wasn't trying non-stop at all.  But I've
made it do that now.  Here's v3, then.  Nothing else changed.

WDYT?

---------
[PATCH] 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, even if other threads are still running.  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 patch adds a new
test that covers this.  It fails in all-stop mode before this patch.

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/
2014-09-19  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/
2014-09-19  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/
2014-09-19  Pedro Alves  <palves@redhat.com>

	* gdb.threads/break-while-running.exp: New file.
	* gdb.threads/break-while-running.c: New file.
---
 gdb/NEWS                                          |   7 ++
 gdb/breakpoint.c                                  |  90 +++++++++-------
 gdb/breakpoint.h                                  |   2 +-
 gdb/doc/gdb.texinfo                               |  13 +--
 gdb/infrun.c                                      |   5 +-
 gdb/remote.c                                      |   5 +-
 gdb/testsuite/gdb.threads/break-while-running.c   |  49 +++++++++
 gdb/testsuite/gdb.threads/break-while-running.exp | 124 ++++++++++++++++++++++
 8 files changed, 240 insertions(+), 55 deletions(-)
 create mode 100644 gdb/testsuite/gdb.threads/break-while-running.c
 create mode 100644 gdb/testsuite/gdb.threads/break-while-running.exp

diff --git a/gdb/NEWS b/gdb/NEWS
index 343ee49..ac94874 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -31,6 +31,13 @@ queue-signal signal-name-or-number
   confirmation if the program had stopped for a signal and the user
   switched threads meanwhile.
 
+* "breakpoint always-inserted" modes "off" and "auto" merged.
+
+  Now, when 'breakpoint always-inserted mode' is set to "off", GDB
+  won't remove breakpoints from the target until all threads stop,
+  even in non-stop mode.  The "auto" mode has been removed, and "off"
+  is now the default mode.
+
 *** Changes in GDB 7.8
 
 * New command line options
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,
diff --git a/gdb/breakpoint.h b/gdb/breakpoint.h
index 00c8802..e191c10 100644
--- a/gdb/breakpoint.h
+++ b/gdb/breakpoint.h
@@ -1491,7 +1491,7 @@ extern void breakpoint_xfer_memory (gdb_byte *readbuf, gdb_byte *writebuf,
 				    const gdb_byte *writebuf_org,
 				    ULONGEST memaddr, LONGEST len);
 
-extern int breakpoints_always_inserted_mode (void);
+extern int breakpoints_should_be_inserted_now (void);
 
 /* Called each time new event from target is processed.
    Retires previously deleted breakpoint locations that
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 1bb1c0c..537fae8 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -3850,22 +3850,13 @@ This behavior can be controlled with the following commands::
 @item set breakpoint always-inserted off
 All breakpoints, including newly added by the user, are inserted in
 the target only when the target is resumed.  All breakpoints are
-removed from the target when it stops.
+removed from the target when it stops.  This is the default mode.
 
 @item set breakpoint always-inserted on
 Causes all breakpoints to be inserted in the target at all times.  If
 the user adds a new breakpoint, or changes an existing breakpoint, the
 breakpoints in the target are updated immediately.  A breakpoint is
-removed from the target only when breakpoint itself is removed.
-
-@cindex non-stop mode, and @code{breakpoint always-inserted}
-@item set breakpoint always-inserted auto
-This is the default mode.  If @value{GDBN} is controlling the inferior
-in non-stop mode (@pxref{Non-Stop Mode}), gdb behaves as if
-@code{breakpoint always-inserted} mode is on.  If @value{GDBN} is
-controlling the inferior in all-stop mode, @value{GDBN} behaves as if
-@code{breakpoint always-inserted} mode is off.
-@end table
+removed from the target only when breakpoint itself is deleted.
 
 @value{GDBN} handles conditional breakpoints by evaluating these conditions
 when a breakpoint breaks.  If the condition is true, then the process being
diff --git a/gdb/infrun.c b/gdb/infrun.c
index c18267f..3725f2d 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -3448,8 +3448,7 @@ handle_inferior_event (struct execution_control_state *ecs)
 	{
 	  /* Loading of shared libraries might have changed breakpoint
 	     addresses.  Make sure new breakpoints are inserted.  */
-	  if (stop_soon == NO_STOP_QUIETLY
-	      && !breakpoints_always_inserted_mode ())
+	  if (stop_soon == NO_STOP_QUIETLY)
 	    insert_breakpoints ();
 	  resume (0, GDB_SIGNAL_0);
 	  prepare_to_wait (ecs);
@@ -6110,7 +6109,7 @@ normal_stop (void)
       printf_filtered (_("No unwaited-for children left.\n"));
     }
 
-  if (!breakpoints_always_inserted_mode () && target_has_execution)
+  if (!breakpoints_should_be_inserted_now () && target_has_execution)
     {
       if (remove_breakpoints ())
 	{
diff --git a/gdb/remote.c b/gdb/remote.c
index 357e9f2..41ea012 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -3604,9 +3604,8 @@ remote_start_remote (int from_tty, struct target_ops *target, int extended_p)
      up.  */
   rs->starting_up = 0;
 
-  /* If breakpoints are global, insert them now.  */
-  if (gdbarch_has_global_breakpoints (target_gdbarch ())
-      && breakpoints_always_inserted_mode ())
+  /* Maybe breakpoints are global and need to be inserted now.  */
+  if (breakpoints_should_be_inserted_now ())
     insert_breakpoints ();
 }
 
diff --git a/gdb/testsuite/gdb.threads/break-while-running.c b/gdb/testsuite/gdb.threads/break-while-running.c
new file mode 100644
index 0000000..3c3a984
--- /dev/null
+++ b/gdb/testsuite/gdb.threads/break-while-running.c
@@ -0,0 +1,49 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2014 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <pthread.h>
+#include <assert.h>
+#include <unistd.h>
+#include <stdlib.h>
+
+volatile unsigned int counter = 1;
+
+void *
+child_function (void *arg)
+{
+  while (counter > 0)
+    {
+      counter++; /* breakpoint A child here */
+      usleep (1); /* breakpoint B child here */
+    }
+
+  pthread_exit (NULL);
+}
+
+int
+main (void)
+{
+  pthread_t child_thread;
+  int res;
+
+  res = pthread_create (&child_thread, NULL, child_function, NULL);
+  assert (res == 0);
+
+  pthread_join (child_thread, NULL);
+
+  exit (EXIT_SUCCESS);
+}
diff --git a/gdb/testsuite/gdb.threads/break-while-running.exp b/gdb/testsuite/gdb.threads/break-while-running.exp
new file mode 100644
index 0000000..5b889a6
--- /dev/null
+++ b/gdb/testsuite/gdb.threads/break-while-running.exp
@@ -0,0 +1,124 @@
+# Copyright (C) 2014 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Test that setting a breakpoint while a thread is running results in
+# the breakpoint being inserted.
+
+standard_testfile
+
+if {[prepare_for_testing "failed to prepare" $testfile $srcfile {debug pthreads}] == -1} {
+    return -1
+}
+
+# The test proper.  NON_STOP is a boolean that indicates whether we're
+# testing in non-stop, or all-stop mode.
+
+proc test { non_stop } {
+    global srcfile binfile
+    global gdb_prompt
+    global decimal
+
+    clean_restart $binfile
+
+    if $non_stop {
+	gdb_test_no_output "set non-stop on"
+    }
+
+    if ![runto_main] {
+	continue
+    }
+
+    # In all-stop, check whether we're testing with the remote or
+    # extended-remote targets.  If so, skip the tests, as with the
+    # RSP, we can't issue commands until the target replies to vCont.
+    # Not an issue with the non-stop RSP variant, which has a
+    # non-blocking vCont.
+    if { !$non_stop && [gdb_is_target_remote] } {
+	return -1
+    }
+
+    gdb_breakpoint [gdb_get_line_number "breakpoint A child here"]
+    gdb_continue_to_breakpoint "run to child breakpoint"
+
+    delete_breakpoints
+
+    # Leave one thread stopped, so GDB can poke at memory freely.
+    if !$non_stop {
+	gdb_test_no_output "set scheduler-locking on"
+	gdb_test "continue &" "Continuing\."
+	gdb_test "thread 1" "Switching to .*" "switch back to main thread"
+    } else {
+	gdb_test "thread 2" "Switching to .*" "switch to event thread"
+	gdb_test "continue &" "Continuing\."
+	gdb_test "thread 1" "Switching to .*" "switch back to main thread"
+
+	set test "interrupt thread"
+	gdb_test_multiple "interrupt" "$test" {
+	    -re "$gdb_prompt" {
+		pass $test
+	    }
+	}
+
+	set test "wait for stop"
+	gdb_test_multiple "" "$test" {
+	    -re " stopped\." {
+		pass $test
+	    }
+	}
+    }
+
+    set test "one and only one thread running"
+    gdb_test_multiple "info threads" $test {
+	-re "\\\(running\\\).*\\\(running\\\).*$gdb_prompt $" {
+	    fail $test
+	}
+	-re "\\\(running\\\).*$gdb_prompt $" {
+	    pass $test
+	}
+    }
+
+    set linenum [gdb_get_line_number "breakpoint B child here"]
+
+    # Don't use gdb_test as it's racy in this case -- gdb_test matches
+    # the prompt with an end anchor.  Sometimes expect will manage to
+    # read the breakpoint hit output while still processing this test,
+    # defeating the anchor.
+    set test "set breakpoint while a thread is running"
+    gdb_test_multiple "break $srcfile:$linenum" $test {
+	-re "Breakpoint $decimal at .*: file .*$srcfile, line $linenum.\r\n$gdb_prompt " {
+	    pass $test
+	}
+	-re "$gdb_prompt " {
+	    fail $test
+	}
+    }
+
+    # Check that the breakpoint is hit.  Can't use gdb_test here, as
+    # no prompt is expected to come out.
+    set test "breakpoint is hit"
+    gdb_test_multiple "" $test {
+	-re "Breakpoint .*, child_function.*break-while-running.c:$linenum.*breakpoint B child here.*" {
+	    pass $test
+	}
+    }
+}
+
+with_test_prefix "all-stop" {
+    test false
+}
+
+with_test_prefix "non-stop" {
+    test true
+}
-- 
1.9.3