Re: dwarf2 - multiple DW_TAG_variable for global variable

[Nenad Vukicevic <nenad@intrepid.com>]

This dwarf code started appearing since this patch:

------------------------------------------------------------------------
r145293 | jakub | 2009-03-30 14:35:03 +0000 (Mon, 30 Mar 2009) | 11 lines

         PR debug/39563
         * c-decl.c (struct c_binding): Add locus field.
         (bind): Add locus argument, set locus field from it.
         (pop_scope): For b->nested VAR_DECL or FUNCTION_DECL,
         add a DECL_EXTERNAL copy of b->decl to current BLOCK_VARS.
         (push_file_scope, pushtag, pushdecl, pushdecl_top_level,
         implicitly_declare, undeclared_variable, lookup_label,
         declare_label, c_make_fname_decl, c_builtin_function,
         c_builtin_function_ext_scope, store_parm_decls_newstyle): Adjust
         bind callers.

Jan, can you confirm that this is indeed the correct DWARF that is being generated.

Thank you,
Nenad



On 1/4/10 11:34 PM, Nenad Vukicevic wrote:
> I installed gcc-4.5-20091224 snapshot and noticed that for simple 
> variable declaration
> I get two DW_TAG_variable dies in the object file. For example, the 
> following
> code
>
> int xxxxx;
> main()
> {xxxxx=1;}
>
> generates (with -g -gdwarf2 -O0 switches):
>
> <1><54>: Abbrev Number: 4 (DW_TAG_variable)
> <55>   DW_AT_name        : (indirect string, offset: 0x36): xxxxx
> <59>   DW_AT_decl_file   : 1
> <5a>   DW_AT_decl_line   : 1
> <5b>   DW_AT_type        : <0x4d>
> <5f>   DW_AT_external    : 1
> <60>   DW_AT_declaration : 1
> <1><61>: Abbrev Number: 5 (DW_TAG_variable)
> <62>   DW_AT_name        : (indirect string, offset: 0x36): xxxxx
> <66>   DW_AT_decl_file   : 1
> <67>   DW_AT_decl_line   : 1
> <68>   DW_AT_type        : <0x4d>
> <6c>   DW_AT_external    : 1
> <6d>   DW_AT_location    : 9 byte block: 3 0 0 0 0 0 0 0 0  
> (DW_OP_addr: 0)
>
> Is the above normal? 4.3.2 compiler generates only one die, the second 
> one with
> DW_AT_location attribute, which is correct.
>
> I also noticed that this example (were variable is not used):
>
> int xxxxx;
> main()
> {}
>
> generates only one DW_TAG_variable, the one  with DW_AT_location, 
> which again
> should be correct.
>
> I ran into this problem by porting some GDB code that uses DWARF2 and 
> got surprised
> to see this change from the previous version of gcc (4.3).
>
> Thanks,
> Nenad
>