[PATCH] gdb: Restore selected frame in print_frame_local_vars

Andrew Burgess andrew.burgess@embecosm.com
Tue May 22 21:53:00 GMT 2018


Simon,

Thanks for your feedback.  I've addressed most of your feedback in
this revision, there's a couple of points I've replied too inline.

* Simon Marchi <simark@simark.ca> [2018-05-20 23:00:13 -0400]:

> On 2018-05-19 06:08 PM, Andrew Burgess wrote:
> > PR gdb/23203 reports 'bt full' causing the currently selected frame to
> > change, this issue is fixed in this commit.
> > 
> > Add a new class scoped_restore_selected_frame that saves and restores
> > the selected frame.  Make use of this in print_frame_local_vars to
> > restore the selected frame on exit.
> 
> Hi Andrew,
> 
> Thanks for the patch.  I noted some comments and questions below, but
> overall this looks great, thanks for taking the time to do this.
> 
> > gdb/ChangeLog:
> > 
> > 	PR gdb/23203
> > 	* frame.c
> > 	(scoped_restore_selected_frame::scoped_restore_selected_frame):
> > 	Define.
> > 	(scoped_restore_selected_frame::~scoped_restore_selected_frame):
> > 	Define.
> > 	* frame.h (class scoped_restore_selected_frame): New class.
> > 	* stack.c (print_frame_local_vars): Remove catching and rethrowing
> > 	of any exception, use scoped_restore_selected_frame to restore the
> > 	frame instead.
> > 
> > gdb/testsuite/ChangeLog:
> > 
> > 	PR gdb/23203
> > 	* gdb.base/bt-full.c: New file.
> > 	* gdb.base/bt-full.exp: New file.
> > ---
> >  gdb/ChangeLog                      | 13 +++++++++
> >  gdb/frame.c                        | 16 ++++++++++
> >  gdb/frame.h                        | 16 ++++++++++
> >  gdb/stack.c                        | 24 +++------------
> >  gdb/testsuite/ChangeLog            |  6 ++++
> >  gdb/testsuite/gdb.base/bt-full.c   | 35 ++++++++++++++++++++++
> >  gdb/testsuite/gdb.base/bt-full.exp | 60 ++++++++++++++++++++++++++++++++++++++
> >  7 files changed, 150 insertions(+), 20 deletions(-)
> >  create mode 100644 gdb/testsuite/gdb.base/bt-full.c
> >  create mode 100644 gdb/testsuite/gdb.base/bt-full.exp
> > 
> > diff --git a/gdb/frame.c b/gdb/frame.c
> > index 07fa2bc77d6..3e42aa82398 100644
> > --- a/gdb/frame.c
> > +++ b/gdb/frame.c
> > @@ -269,6 +269,22 @@ frame_stash_invalidate (void)
> >    htab_empty (frame_stash);
> >  }
> >  
> > +/* Save the currently selected frame.  */
> 
> Please put the doc in the header file, and put /* See frame.h.  */ here.
> 
> > +scoped_restore_selected_frame::scoped_restore_selected_frame ()
> > +{
> > +  m_fid = get_frame_id (get_selected_frame (NULL));
> > +}
> > +
> > +/* Restore the currently selected frame.  */
> 
> Here too.
> 
> > +scoped_restore_selected_frame::~scoped_restore_selected_frame ()
> > +{
> > +  frame_info *frame = frame_find_by_id (m_fid);
> > +  if (frame == NULL)
> > +    warning (_("Unable to restore previously selected frame."));
> > +  else
> > +    select_frame (frame);
> > +}
> > +
> >  /* Flag to control debugging.  */
> >  
> >  unsigned int frame_debug;
> > diff --git a/gdb/frame.h b/gdb/frame.h
> > index d5800b78c25..2c8f815a4ae 100644
> > --- a/gdb/frame.h
> > +++ b/gdb/frame.h
> > @@ -164,6 +164,22 @@ struct frame_id
> >    int artificial_depth;
> >  };
> >  
> > +/* Save and restore the currently selected frame.  */
> > +
> > +class scoped_restore_selected_frame
> > +{
> > +public:
> > +  scoped_restore_selected_frame ();
> > +  ~scoped_restore_selected_frame ();
> > +
> > +  DISABLE_COPY_AND_ASSIGN (scoped_restore_selected_frame);
> > +
> > +private:
> > +
> > +  /* The ID of the previously selected frame.  */
> > +  struct frame_id m_fid;
> > +};
> > +
> >  /* Methods for constructing and comparing Frame IDs.  */
> >  
> >  /* For convenience.  All fields are zero.  This means "there is no frame".  */
> > diff --git a/gdb/stack.c b/gdb/stack.c
> > index ecf1ee83793..7e377764865 100644
> > --- a/gdb/stack.c
> > +++ b/gdb/stack.c
> > @@ -2019,7 +2019,6 @@ print_frame_local_vars (struct frame_info *frame, int num_tabs,
> >    struct print_variable_and_value_data cb_data;
> >    const struct block *block;
> >    CORE_ADDR pc;
> > -  struct gdb_exception except = exception_none;
> >  
> >    if (!get_frame_pc_if_available (frame, &pc))
> >      {
> > @@ -2043,27 +2042,12 @@ print_frame_local_vars (struct frame_info *frame, int num_tabs,
> >    /* Temporarily change the selected frame to the given FRAME.
> >       This allows routines that rely on the selected frame instead
> >       of being given a frame as parameter to use the correct frame.  */
> > +  scoped_restore_selected_frame restore_selected_frame;
> 
> Should we instead put this scoped_restore in the caller, so we only save/restore the
> frame once during the execution of "bt full"?

I'm inclined not to, so that print_frame_local_vars doesn't end up
changing the frame.  However, I'm not that fussed, so if you'd really
prefer it done differently then I'm happy to make that change.

> 
> >    select_frame (frame);
> >  
> > -  TRY
> > -    {
> > -      iterate_over_block_local_vars (block,
> > -				     do_print_variable_and_value,
> > -				     &cb_data);
> > -    }
> > -  CATCH (ex, RETURN_MASK_ALL)
> > -    {
> > -      except = ex;
> > -    }
> > -  END_CATCH
> > -
> > -  /* Restore the selected frame, and then rethrow if there was a problem.  */
> > -  select_frame (frame_find_by_id (cb_data.frame_id));
> > -  if (except.reason < 0)
> > -    throw_exception (except);
> > -
> > -  /* do_print_variable_and_value invalidates FRAME.  */
> > -  frame = NULL;
> > +  iterate_over_block_local_vars (block,
> > +				 do_print_variable_and_value,
> > +				 &cb_data);
> >  
> >    if (!cb_data.values_printed)
> >      fprintf_filtered (stream, _("No locals.\n"));
> > diff --git a/gdb/testsuite/gdb.base/bt-full.c b/gdb/testsuite/gdb.base/bt-full.c
> > new file mode 100644
> > index 00000000000..708dc69b250
> > --- /dev/null
> > +++ b/gdb/testsuite/gdb.base/bt-full.c
> > @@ -0,0 +1,35 @@
> > +/* This testcase is part of GDB, the GNU debugger.
> > +
> > +   Copyright 2018 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/>.  */
> > +
> > +void
> > +breakpt ()
> > +{
> > +  asm ("" ::: "memory");
> > +}
> > +
> > +void
> > +func ()
> > +{
> > +  breakpt ();
> > +}
> > +
> > +int
> > +main ()
> > +{
> > +  func ();
> > +  return 0;
> > +}
> > diff --git a/gdb/testsuite/gdb.base/bt-full.exp b/gdb/testsuite/gdb.base/bt-full.exp
> > new file mode 100644
> > index 00000000000..7b64293dcfb
> > --- /dev/null
> > +++ b/gdb/testsuite/gdb.base/bt-full.exp
> > @@ -0,0 +1,60 @@
> > +# Copyright 2018 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/>.
> > +
> > +standard_testfile
> > +
> > +if { [prepare_for_testing "failed to prepare" $testfile $srcfile debug] } {
> > +    return -1
> > +}
> > +
> > +if ![runto_main] then {
> > +    fail "can't run to main"
> > +    return 0
> > +}
> > +
> > +gdb_breakpoint "breakpt"
> > +gdb_continue_to_breakpoint "breakpt"
> > +
> > +# Return the frame number for the currently selected frame
> > +proc get_current_frame_number {{test_name ""}} {
> > +    global gdb_prompt
> > +
> > +    if { $test_name == "" } {
> > +	set test_name "get current frame number"
> > +    }
> > +    set frame_num -1
> > +    gdb_test_multiple "frame" $test_name {
> > +	-re "#(\[0-9\]+) .*$gdb_prompt $" {
> > +	    set frame_num $expect_out(1,string)
> > +	}
> > +    }
> > +    return $frame_num
> > +}
> 
> This could go in lib/gdb.exp I suppose.
> 
> > +
> > +# Visit each frame in the stack and ensure that 'bt full' doesn't
> > +# change the selected stack frame.
> > +for {set i 0} {$i < 3} {incr i} {
> 
> I have a personal preference for this style:
> 
>   foreach_with_prefix frame {1 2 3} {
>     ...
>   }
> 
> I think it expresses the intent better than a simple for loop, and it automatically
> scopes the test messages (with frame=X), so you don't need to put $i in every test
> message.
> 
> > +    if { $i == 0 } {
> > +	gdb_assert {[get_current_frame_number] == $i} "check frame $i is selected"
> > +    } else {
> > +	gdb_test "frame $i" "#$i .*" "select frame $i"
> > +    }
> 
> Is there a particular reason for this if?  Could we not do both "frame $i" and check
> the current frame at every iteration?

I'd prefer to keep things as they are.  The code as it currently is
checks that we are in frame 0 when we stop at the breakpoint.  Sure
this is checked many times elsewhere, but it doesn't hurt to check it
again.

We could move the gdb_assert outside the if/then/else, but we already
check that the frame number changes after the 'frame <N>' in the
regexp, so I don't think moving the gdb_assert adds anything.

Again, I'm not that fussed, so if you feel strongly, let me know and
I'll change it as you suggested.

> 
> > +
> > +    gdb_test "bt full" "#0 \[^\n\r\]+\[\n\r\]+No locals\.\[\n\r\]+#1 \[^\n\r\]+\[\n\r\]+No locals\.\[\n\r\]+#2 \[^\n\r\]+\[\n\r\]+No locals\.\[\n\r\]+" \
> > +	"perform 'bt full' in frame $i"
> 
> Did you try using the multi_line proc?  It might help make this more readable.
> 
> > +
> > +    gdb_assert {[get_current_frame_number] == $i} "check frame $i is still selected"
> > +}
> > +
> > 
> 
> Is there already a test that does the equivalent of this, but for "bt" not-full?  It might
> not be really necessary, but I thought it would be a low-hanging fruit to test with both
> "bt" and "bt-fulL" at this point.  Obviously, the test wouldn't be
> named bt-full.exp then :).

I renamed the test, and extended it to cover 'bt' as well as 'bt full'.

Thanks,
Andrew

---

gdb: Restore selected frame in print_frame_local_vars

PR gdb/23203 reports 'bt full' causing the currently selected frame to
change, this issue is fixed in this commit.

Add a new class scoped_restore_selected_frame that saves and restores
the selected frame.  Make use of this in print_frame_local_vars to
restore the selected frame on exit.

gdb/ChangeLog:

	PR gdb/23203
	* frame.c
	(scoped_restore_selected_frame::scoped_restore_selected_frame):
	Define.
	(scoped_restore_selected_frame::~scoped_restore_selected_frame):
	Define.
	* frame.h (class scoped_restore_selected_frame): New class.
	* stack.c (print_frame_local_vars): Remove catching and rethrowing
	of any exception, use scoped_restore_selected_frame to restore the
	frame instead.

gdb/testsuite/ChangeLog:

	PR gdb/23203
	* gdb.base/bt-selected-frame.c: New file.
	* gdb.base/bt-selected-frame.exp: New file.
	* lib/gdb.exp (get_current_frame_number): New function.
---
 gdb/ChangeLog                                | 13 ++++++
 gdb/frame.c                                  | 16 +++++++
 gdb/frame.h                                  | 19 ++++++++
 gdb/stack.c                                  | 24 ++--------
 gdb/testsuite/ChangeLog                      |  7 +++
 gdb/testsuite/gdb.base/bt-selected-frame.c   | 35 ++++++++++++++
 gdb/testsuite/gdb.base/bt-selected-frame.exp | 70 ++++++++++++++++++++++++++++
 gdb/testsuite/lib/gdb.exp                    | 16 +++++++
 8 files changed, 180 insertions(+), 20 deletions(-)
 create mode 100644 gdb/testsuite/gdb.base/bt-selected-frame.c
 create mode 100644 gdb/testsuite/gdb.base/bt-selected-frame.exp

diff --git a/gdb/frame.c b/gdb/frame.c
index 07fa2bc77d6..1d0eb725145 100644
--- a/gdb/frame.c
+++ b/gdb/frame.c
@@ -269,6 +269,22 @@ frame_stash_invalidate (void)
   htab_empty (frame_stash);
 }
 
+/* See frame.h  */
+scoped_restore_selected_frame::scoped_restore_selected_frame ()
+{
+  m_fid = get_frame_id (get_selected_frame (NULL));
+}
+
+/* See frame.h  */
+scoped_restore_selected_frame::~scoped_restore_selected_frame ()
+{
+  frame_info *frame = frame_find_by_id (m_fid);
+  if (frame == NULL)
+    warning (_("Unable to restore previously selected frame."));
+  else
+    select_frame (frame);
+}
+
 /* Flag to control debugging.  */
 
 unsigned int frame_debug;
diff --git a/gdb/frame.h b/gdb/frame.h
index d5800b78c25..a6f7fd8947d 100644
--- a/gdb/frame.h
+++ b/gdb/frame.h
@@ -164,6 +164,25 @@ struct frame_id
   int artificial_depth;
 };
 
+/* Save and restore the currently selected frame.  */
+
+class scoped_restore_selected_frame
+{
+public:
+  /* Save the currently selected frame.  */
+  scoped_restore_selected_frame ();
+
+  /* Restore the currently selected frame.  */
+  ~scoped_restore_selected_frame ();
+
+  DISABLE_COPY_AND_ASSIGN (scoped_restore_selected_frame);
+
+private:
+
+  /* The ID of the previously selected frame.  */
+  struct frame_id m_fid;
+};
+
 /* Methods for constructing and comparing Frame IDs.  */
 
 /* For convenience.  All fields are zero.  This means "there is no frame".  */
diff --git a/gdb/stack.c b/gdb/stack.c
index ecf1ee83793..7e377764865 100644
--- a/gdb/stack.c
+++ b/gdb/stack.c
@@ -2019,7 +2019,6 @@ print_frame_local_vars (struct frame_info *frame, int num_tabs,
   struct print_variable_and_value_data cb_data;
   const struct block *block;
   CORE_ADDR pc;
-  struct gdb_exception except = exception_none;
 
   if (!get_frame_pc_if_available (frame, &pc))
     {
@@ -2043,27 +2042,12 @@ print_frame_local_vars (struct frame_info *frame, int num_tabs,
   /* Temporarily change the selected frame to the given FRAME.
      This allows routines that rely on the selected frame instead
      of being given a frame as parameter to use the correct frame.  */
+  scoped_restore_selected_frame restore_selected_frame;
   select_frame (frame);
 
-  TRY
-    {
-      iterate_over_block_local_vars (block,
-				     do_print_variable_and_value,
-				     &cb_data);
-    }
-  CATCH (ex, RETURN_MASK_ALL)
-    {
-      except = ex;
-    }
-  END_CATCH
-
-  /* Restore the selected frame, and then rethrow if there was a problem.  */
-  select_frame (frame_find_by_id (cb_data.frame_id));
-  if (except.reason < 0)
-    throw_exception (except);
-
-  /* do_print_variable_and_value invalidates FRAME.  */
-  frame = NULL;
+  iterate_over_block_local_vars (block,
+				 do_print_variable_and_value,
+				 &cb_data);
 
   if (!cb_data.values_printed)
     fprintf_filtered (stream, _("No locals.\n"));
diff --git a/gdb/testsuite/gdb.base/bt-selected-frame.c b/gdb/testsuite/gdb.base/bt-selected-frame.c
new file mode 100644
index 00000000000..708dc69b250
--- /dev/null
+++ b/gdb/testsuite/gdb.base/bt-selected-frame.c
@@ -0,0 +1,35 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2018 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/>.  */
+
+void
+breakpt ()
+{
+  asm ("" ::: "memory");
+}
+
+void
+func ()
+{
+  breakpt ();
+}
+
+int
+main ()
+{
+  func ();
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.base/bt-selected-frame.exp b/gdb/testsuite/gdb.base/bt-selected-frame.exp
new file mode 100644
index 00000000000..931c91018c9
--- /dev/null
+++ b/gdb/testsuite/gdb.base/bt-selected-frame.exp
@@ -0,0 +1,70 @@
+# Copyright 2018 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/>.
+
+standard_testfile
+
+if { [prepare_for_testing "failed to prepare" $testfile $srcfile debug] } {
+    return -1
+}
+
+proc check_selected_frame_after_bt { bt_cmd stack_pattern } {
+    global binfile
+
+    clean_restart $binfile
+
+    with_test_prefix $bt_cmd {
+
+	if ![runto_main] then {
+	    fail "can't run to main"
+	    return 0
+	}
+
+	gdb_breakpoint "breakpt"
+	gdb_continue_to_breakpoint "breakpt"
+
+	# Visit each frame in the stack and ensure that the selected
+	# frame doesn't change after executing the backtrace command
+	# in BT_CMD.
+	foreach_with_prefix frame {0 1 2} {
+	    if { $frame == 0 } {
+		gdb_assert {[get_current_frame_number] == $frame} \
+		    "check frame"
+	    } else {
+		gdb_test "frame $frame" "#$frame .*" "select frame"
+	    }
+
+	    gdb_test "$bt_cmd" $stack_pattern \
+		"perform backtrace command"
+
+	    gdb_assert {[get_current_frame_number] == $frame} \
+		"check frame is still selected"
+	}
+    }
+}
+
+check_selected_frame_after_bt "bt" \
+    [multi_line          \
+	 "#0 \[^\n\r\]+" \
+	 "#1 \[^\n\r\]+" \
+	 "#2 \[^\n\r\]+"]
+
+check_selected_frame_after_bt "bt full" \
+    [multi_line          \
+	 "#0 \[^\n\r\]+" \
+	 "No locals\."   \
+	 "#1 \[^\n\r\]+" \
+	 "No locals\."   \
+	 "#2 \[^\n\r\]+" \
+	 "No locals\."]
diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index 0f05d043f25..ee66a38e08f 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -5805,6 +5805,22 @@ proc get_var_address { var } {
     return ""
 }
 
+# Return the frame number for the currently selected frame
+proc get_current_frame_number {{test_name ""}} {
+    global gdb_prompt
+
+    if { $test_name == "" } {
+	set test_name "get current frame number"
+    }
+    set frame_num -1
+    gdb_test_multiple "frame" $test_name {
+	-re "#(\[0-9\]+) .*$gdb_prompt $" {
+	    set frame_num $expect_out(1,string)
+	}
+    }
+    return $frame_num
+}
+
 # Get the current value for remotetimeout and return it.
 proc get_remotetimeout { } {
     global gdb_prompt
-- 
2.14.3



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