bug#21438: 25.0.50; GUD locals frame/window doesn't shows struct values as nil

bug#21438: 25.0.50; GUD locals frame/window doesn't shows struct values as nil

[Tassilo Horn]

When debugging C code with M-x gdb and enabling the locals window or
frame, the values of structs (just structs, no struct pointers) are
always displayed as nil.  For example, when debugging in xdisp.c

--8<---------------cut here---------------start------------->8---
DEFUN ("line-pixel-height", Fline_pixel_height,
       Sline_pixel_height, 0, 0, 0,
       doc: /* Return height in pixels of text line in the selected window.

Value is the height in pixels of the line at point.  */)
  (void)
{
  struct it it;
  struct text_pos pt;
  struct window *w = XWINDOW (selected_window);
  struct buffer *old_buffer = NULL;
  Lisp_Object result;
  ...
}
--8<---------------cut here---------------end--------------->8---

and stepping till the end of the function, this is the contents of the
locals buffer shows:

--8<---------------cut here---------------start------------->8---
struct it       it         nil
struct text_pos pt         nil
struct window * w          0x12a1d40
struct buffer * old_buffer 0x0
Lisp_Object     result     58
--8<---------------cut here---------------end--------------->8---

But it and pt cannot be NULL/nil (and they are not when checking with
"info locals" in the GUD GDB buffer).

The reason for that is that GUD uses the GDB command "-stack-list-locals
--thread X --simple-values" as defined in gdb-mi.el:3991 which returns:

  locals=[{name="it",type="struct it"},
          {name="pt",type="struct text_pos"},
          {name="w",type="struct window *",value="0x12a1d40"},
          {name="old_buffer",type="struct buffer *",value="0x0"},
          {name="result",type="Lisp_Object",value="58"}]

Note that the entries for the two structs it and pt don't have a value
field.

I guess the usage of --simple-values is intentional, and in fact, when
trying to use "--all-values" instead I get a

  error in process filter: gdb-jsonify-buffer: Stack overflow in regexp matcher

I'm not actually sure if it would be benefitical to use --all-values
even if that regexp matching error was fixed because the structs can be
really large.  But at least the value should not be shown as "nil" but
as "<non-simple value>" or something else which makes it obvious that
the displayed value is not the real value.



In GNU Emacs 25.0.50.15 (x86_64-unknown-linux-gnu, GTK+ Version 3.16.6)
 of 2015-09-09
Repository revision: 39dca94701de81d02c75316e32d67e3677bd685d
Windowing system distributor 'The X.Org Foundation', version 11.0.11702000
System Description:	Arch Linux

Configured using:
 'configure 'CFLAGS=-g -ggdb3 -O0''

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GCONF GSETTINGS
NOTIFY ACL GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11

Important settings:
  value of $LC_MONETARY: de_DE.utf8
  value of $LC_NUMERIC: de_DE.utf8
  value of $LC_TIME: de_DE.utf8
  value of $LANG: en_US.utf8
  locale-coding-system: utf-8-unix

Major mode: Debugger

Minor modes in effect:
  diff-auto-refine-mode: t
  global-company-mode: t
  shell-dirtrack-mode: t
  global-aggressive-indent-mode: t
  pdf-occur-global-minor-mode: t
  recentf-mode: t
  global-subword-mode: t
  subword-mode: t
  save-place-mode: t
  savehist-mode: t
  show-paren-mode: t
  ivy-mode: t
  minibuffer-depth-indicate-mode: t
  electric-pair-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent messages:
Type C-x 1 to delete the help window.
mouse-2, RET: find function's definition
Unable to find location in file
Entering debugger...
Back to top level
Quit
"-stack-list-locals --thread 1"
Quit
"-stack-list-locals --thread 1 --simple-values"
Mark set [2 times]
Quit [3 times]

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bug#21438: 25.0.50; GUD locals frame/window doesn't shows struct values as nil

[Eli Zaretskii]

> From: Tassilo Horn <tsdh@gnu.org>
> Date: Wed, 09 Sep 2015 08:04:49 +0200
> 
> stepping till the end of the function, this is the contents of the
> locals buffer shows:
> 
> --8<---------------cut here---------------start------------->8---
> struct it       it         nil
> struct text_pos pt         nil
> struct window * w          0x12a1d40
> struct buffer * old_buffer 0x0
> Lisp_Object     result     58
> --8<---------------cut here---------------end--------------->8---
> 
> But it and pt cannot be NULL/nil (and they are not when checking with
> "info locals" in the GUD GDB buffer).
> 
> The reason for that is that GUD uses the GDB command "-stack-list-locals
> --thread X --simple-values" as defined in gdb-mi.el:3991 which returns:
> 
>   locals=[{name="it",type="struct it"},
>           {name="pt",type="struct text_pos"},
>           {name="w",type="struct window *",value="0x12a1d40"},
>           {name="old_buffer",type="struct buffer *",value="0x0"},
>           {name="result",type="Lisp_Object",value="58"}]
> 
> Note that the entries for the two structs it and pt don't have a value
> field.
> 
> I guess the usage of --simple-values is intentional, and in fact, when
> trying to use "--all-values" instead I get a
> 
>   error in process filter: gdb-jsonify-buffer: Stack overflow in regexp matcher

Yes, the use of --simple-values is intentional.  If you want to see
the values of the fields, you need to click mouse-2 on the variable
name, and then Emacs will pop up a frame with the fields.

> I'm not actually sure if it would be benefitical to use --all-values
> even if that regexp matching error was fixed because the structs can be
> really large.  But at least the value should not be shown as "nil" but
> as "<non-simple value>" or something else which makes it obvious that
> the displayed value is not the real value.

Like the patch below?  If you think it's OK, I will push it.

Thanks.

--- lisp/progmodes/gdb-mi.el~0	2015-05-20 08:22:42.000000000 +0300
+++ lisp/progmodes/gdb-mi.el	2015-09-09 16:47:24.399310500 +0300
@@ -4038,6 +4038,8 @@
       (let ((name (bindat-get-field local 'name))
             (value (bindat-get-field local 'value))
             (type (bindat-get-field local 'type)))
+        (when (not value)
+          (setq value "<complex data type>"))
         (if (or (not value)
                 (string-match "\\0x" value))
             (add-text-properties 0 (length name)

bug#21438: 25.0.50; GUD locals frame/window doesn't shows struct values as nil

[Tassilo Horn]

Eli Zaretskii <eliz@gnu.org> writes:

>> I guess the usage of --simple-values is intentional, and in fact, when
>> trying to use "--all-values" instead I get a
>> 
>>   error in process filter: gdb-jsonify-buffer: Stack overflow in regexp matcher
>
> Yes, the use of --simple-values is intentional.  If you want to see
> the values of the fields, you need to click mouse-2 on the variable
> name, and then Emacs will pop up a frame with the fields.

Yes, or I can watch the variable and get a nice speedbar tree view which
I can expand recursively.  Really nice!

>> I'm not actually sure if it would be benefitical to use --all-values
>> even if that regexp matching error was fixed because the structs can be
>> really large.  But at least the value should not be shown as "nil" but
>> as "<non-simple value>" or something else which makes it obvious that
>> the displayed value is not the real value.
>
> Like the patch below?  If you think it's OK, I will push it.

Yes, that's exactly what I had in mind.

Bye,
Tassilo

bug#21438: 25.0.50; GUD locals frame/window doesn't shows struct values as nil

[Eli Zaretskii]

> From: Tassilo Horn <tsdh@gnu.org>
> Cc: 21438@debbugs.gnu.org
> Date: Wed, 09 Sep 2015 17:10:10 +0200
> 
> >> I'm not actually sure if it would be benefitical to use --all-values
> >> even if that regexp matching error was fixed because the structs can be
> >> really large.  But at least the value should not be shown as "nil" but
> >> as "<non-simple value>" or something else which makes it obvious that
> >> the displayed value is not the real value.
> >
> > Like the patch below?  If you think it's OK, I will push it.
> 
> Yes, that's exactly what I had in mind.

Thanks, pushed.