Re: Gdb generates location list without DW_AT_frame_base

["H. J. Lu" <hjl at lucon dot org>]

On Thu, Dec 30, 2004 at 07:35:13PM -0500, Daniel Berlin wrote:
> 
> 
> On Thu, 30 Dec 2004, H. J. Lu wrote:
> 
> >On Thu, Dec 30, 2004 at 03:56:33PM -0500, Daniel Berlin wrote:
> >>
> >>>And what's in the location lists?  If it's DW_OP_fbreg, then I presume
> >>>it's a GCC bug.  According to my reading of the DWARF spec, anyway.
> >>It is.
> >>
> >>I added code to tell it when not to use fbreg, but i only told it not to
> >>use fbreg in the location expression when we were outputting the
> >>frame_base attribute.
> >>
> >>However, it appears we don't output a frame base attribute for external
> >>procedures, so we need to tell it it can't use if we don't have a frame
> >>base attribute.
> >>
> >>You just need to change when loc_descriptor is called with a second
> >>parameter of true/1 to fix this.
> >
> >Do you have a patch I can try?
> 
> This may not fix all of them, but it should help.

> Index: dwarf2out.c
> ===================================================================
> RCS file: /cvs/gcc/gcc/gcc/dwarf2out.c,v
> retrieving revision 1.564
> diff -u -p -r1.564 dwarf2out.c
> --- dwarf2out.c	24 Dec 2004 05:23:07 -0000	1.564
> +++ dwarf2out.c	31 Dec 2004 00:34:38 -0000
> @@ -9980,6 +9980,7 @@ add_location_or_const_value_attribute (d
>    rtx rtl;
>    dw_loc_descr_ref descr;
>    var_loc_list *loc_list;
> +  bool can_use_fb = attr != DW_AT_frame_base && !DECL_EXTERNAL (decl);
>  
>    if (TREE_CODE (decl) == ERROR_MARK)
>      return;
> @@ -10049,7 +10050,7 @@ add_location_or_const_value_attribute (d
>  	    varloc = NOTE_VAR_LOCATION (node->var_loc_note);
>  	    add_loc_descr_to_loc_list (&list,
>  				       loc_descriptor (varloc,
> -						       attr != DW_AT_frame_base),
> +						       can_use_fb),
>  				       node->label, node->next->label, secname);
>  	  }
>  
> @@ -10070,7 +10071,7 @@ add_location_or_const_value_attribute (d
>  	    }
>  	  add_loc_descr_to_loc_list (&list,
>  				     loc_descriptor (varloc,
> -						     attr != DW_AT_frame_base),
> +						     can_use_fb),
>  				     node->label, endname, secname);
>  	}
>  

There are several problems with this patch:

1. It checks DECL_EXTERNAL. Did you mean TREE_PUBLIC?
2. It doesn't cover PARM_DECL nor RESULT_DECL.
3. For

#0  loc_descriptor (rtl=0xb7d67abc, can_use_fbreg=1 '\001')
    at /net/gnu/export/gnu/src/gcc/gcc/gcc/dwarf2out.c:8740
#1  0x0813bd45 in loc_descriptor_from_tree_1 (loc=0xb7d60870,
want_address=2)
    at /net/gnu/export/gnu/src/gcc/gcc/gcc/dwarf2out.c:8928
#2  0x0813c2b7 in add_location_or_const_value_attribute
(die=0xb7d66f3c,
    decl=0xb7d60870, attr=DW_AT_location)
    at /net/gnu/export/gnu/src/gcc/gcc/gcc/dwarf2out.c:9247
#3  0x08141ec6 in gen_formal_parameter_die (node=0xb7d60870,
    context_die=0xb7d66ea0)
    at /net/gnu/export/gnu/src/gcc/gcc/gcc/dwarf2out.c:11001
#4  0x0813ded2 in gen_decl_die (decl=0xb7d60870,
context_die=0xb7d66ea0)
    at /net/gnu/export/gnu/src/gcc/gcc/gcc/dwarf2out.c:12700
#5  0x08140479 in gen_subprogram_die (decl=0xb7d601b0,
context_die=0x84da799)
    at /net/gnu/export/gnu/src/gcc/gcc/gcc/dwarf2out.c:11382

it comes from

   8926             /* Certain constructs can only be represented at
top-level.  */
   8927             if (want_address == 2)
   8928               return loc_descriptor (rtl, true);
   8929

H.J.