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-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
  

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"?

>    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?

> +
> +    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 :).

Thanks,

Simon