Re: dwarf2 - multiple DW_TAG_variable for global variable

[Nenad Vukicevic]

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