Debugging Emacs with gdba

Debugging Emacs with gdba

[Nick Roberts]

If you debug Emacs from within Emacs, read on:

I've modified gud-pp to work from the speedbar.  So if you watch a structure
e.g a window, you can place the cursor over one of the components, press
p and display its lisp value in the GUD buffer:

Speedbar:

Watch Expressions:
o	struct window *
 size	1073745994
 vec_next	struct Lisp_Vector *
 frame	140441948
 mini_p	137829369
 next	153394732
 prev	137829369
 hchild	137829369
 vchild	137829369
 parent	137829369
 ...

GUD buffer:

(gdb)
o.next = #<window 4 on  *Minibuf-0*>
(gdb)

It won't work from the tool-bar because that frame takes focus and changes
point to the value in the newly selected window.

Currently it only works on lisp objects which are components of a structure
but I could get it to work on arrays of lisp objects, if they exist in Emacs.

When the cursor is over a value in the speedbar, the tooltip now displays the
data type.  Unfortunately for lisp objects it displays "int".  It would be
nice if it displayed Lisp_Object.  I don't know how to get it to do this,
though.

Nick

Re: Debugging Emacs with gdba

[Eli Zaretskii]

> From: Nick Roberts <nickrob@snap.net.nz>
> Date: Fri, 18 Nov 2005 16:36:17 +1300
> 
> When the cursor is over a value in the speedbar, the tooltip now displays the
> data type.  Unfortunately for lisp objects it displays "int".  It would be
> nice if it displayed Lisp_Object.  I don't know how to get it to do this,
> though.

Does your debug info format support macro expansion?  If it does, you
could try using the `macro *' commands in GDB to display Lisp_Object.

Re: Debugging Emacs with gdba

[Nick Roberts]

 > > When the cursor is over a value in the speedbar, the tooltip now displays
 > > the data type.  Unfortunately for lisp objects it displays "int".  It
 > > would be nice if it displayed Lisp_Object.  I don't know how to get it to
 > > do this, though.
 > 
 > Does your debug info format support macro expansion?  If it does, you
 > could try using the `macro *' commands in GDB to display Lisp_Object.

In fact by using a macro for Lisp_Object, the information is lost.  If I
make the change below, it works.  I think this change is right, in any
case.  If Lisp_Object is a union, its done this way.  And it's generally
useful.  Debugging with GDB from the command line, if you are unsure what
a variable is representing, you can type:

(gdb) whatis new
type = Lisp_Object

instead of getting

(gdb) whatis new
type = int

Is it OK to install this patch?

Nick


*** lisp.h	16 Nov 2005 08:02:46 +1300	1.545
--- lisp.h	19 Nov 2005 11:28:51 +1300	
***************
*** 253,259 ****
  /* If union type is not wanted, define Lisp_Object as just a number.  */
  
  #ifdef NO_UNION_TYPE
! #define Lisp_Object EMACS_INT
  #define LISP_MAKE_RVALUE(o) (0+(o))
  #endif /* NO_UNION_TYPE */
  
--- 253,259 ----
  /* If union type is not wanted, define Lisp_Object as just a number.  */
  
  #ifdef NO_UNION_TYPE
! typedef EMACS_INT Lisp_Object;
  #define LISP_MAKE_RVALUE(o) (0+(o))
  #endif /* NO_UNION_TYPE */

Re: Debugging Emacs with gdba

[Eli Zaretskii]

> From: Nick Roberts <nickrob@snap.net.nz>
> Date: Sat, 19 Nov 2005 11:46:32 +1300
> Cc: emacs-devel@gnu.org
> 
> Is it OK to install this patch?
> 
> Nick
> 
> 
> *** lisp.h	16 Nov 2005 08:02:46 +1300	1.545
> --- lisp.h	19 Nov 2005 11:28:51 +1300	
> ***************
> *** 253,259 ****
>   /* If union type is not wanted, define Lisp_Object as just a number.  */
>   
>   #ifdef NO_UNION_TYPE
> ! #define Lisp_Object EMACS_INT
>   #define LISP_MAKE_RVALUE(o) (0+(o))
>   #endif /* NO_UNION_TYPE */
>   
> --- 253,259 ----
>   /* If union type is not wanted, define Lisp_Object as just a number.  */
>   
>   #ifdef NO_UNION_TYPE
> ! typedef EMACS_INT Lisp_Object;
>   #define LISP_MAKE_RVALUE(o) (0+(o))
>   #endif /* NO_UNION_TYPE */

Fine with me, but please wait for Richard to give the definitive
response.

Meanwhile, I hope you did check that all the x... GDB commands defined
by src/.gdbinit that work with Lisp data types encoded in Lisp_Object
still work after this change (not that I expect them to stop working,
but still...).

Re: Debugging Emacs with gdba

[Richard M. Stallman]

    In fact by using a macro for Lisp_Object, the information is lost.  If I
    make the change below, it works.  I think this change is right, in any
    case.

Please install it, and we will see if there is any drawback for debugging.