Re: FYI: fix latent bug in dw2_find_symbol_file

[Doug Evans <dje@google.com>]

On Mon, Jun 11, 2012 at 11:42 AM, Tom Tromey <tromey@redhat.com> wrote:
> I'm checking this in.
>
> dw2_find_symbol_file has a latent bug.  It assumes that the last file in
> file name table is the primary file name for the CU.
>
> However, there's no reason this must be true.  The primary file name
> could appear anywhere.
>
> And, since this method returns just the file name, and not the directory
> name, there is no reason to even bother reading the line number program
> -- we can just use the CU DIE's DW_AT_name.
>
> I don't have a test case for this; but the situation came up with the
> dwz multifile code.
>
> Built and regtested on x86-64 Fedora 16.
>
> Tom
>
> 2012-06-11  Tom Tromey  <tromey@redhat.com>
>
>        * dwarf2read.c (dw2_get_primary_filename_reader): New function.
>        (dw2_find_symbol_file): Use it.
>
> diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
> index 589361e..7e25d08 100644
> --- a/gdb/dwarf2read.c
> +++ b/gdb/dwarf2read.c
> @@ -2836,12 +2836,34 @@ dw2_expand_symtabs_with_filename (struct objfile *objfile,
>     }
>  }
>
> +/* A helper function for dw2_find_symbol_file that finds the primary
> +   file name for a given CU.  This is a die_reader_func.  */
> +
> +static void
> +dw2_get_primary_filename_reader (const struct die_reader_specs *reader,
> +                                gdb_byte *info_ptr,
> +                                struct die_info *comp_unit_die,
> +                                int has_children,
> +                                void *data)
> +{
> +  const char **result_ptr = data;
> +  struct dwarf2_cu *cu = reader->cu;
> +  struct attribute *attr;
> +
> +  attr = dwarf2_attr (comp_unit_die, DW_AT_name, cu);
> +  if (attr == NULL)
> +    *result_ptr = NULL;
> +  else
> +    *result_ptr = DW_STRING (attr);
> +}
> +
>  static const char *
>  dw2_find_symbol_file (struct objfile *objfile, const char *name)
>  {
>   struct dwarf2_per_cu_data *per_cu;
>   offset_type *vec;
>   struct quick_file_names *file_data;
> +  const char *filename;
>
>   dw2_setup (objfile);
>
> @@ -2873,12 +2895,17 @@ dw2_find_symbol_file (struct objfile *objfile, const char *name)
>   /* vec[0] is the length, which must always be >0.  */
>   per_cu = dw2_get_cu (MAYBE_SWAP (vec[1]));
>
> -  file_data = dw2_get_file_names (objfile, per_cu);
> -  if (file_data == NULL
> -      || file_data->num_file_names == 0)
> -    return NULL;
> +  if (per_cu->v.quick->symtab != NULL)
> +    return per_cu->v.quick->symtab->filename;
> +
> +  if (per_cu->is_debug_types)
> +    init_cutu_and_read_dies (per_cu, 0, 0, dw2_get_primary_filename_reader,
> +                            &filename);
> +  else
> +    init_cutu_and_read_dies_simple (per_cu, dw2_get_primary_filename_reader,
> +                                   &filename);
>
> -  return file_data->file_names[file_data->num_file_names - 1];
> +  return filename;
>  }
>
>  static void

You need to call init_cutu_and_read_dies in both debug-types and
non-debug-types cases.
When DWO files are in use DW_AT_name lives in the DWO file.
OTOH TUs typically don't have DW_AT_name (you need to look at DW_AT_decl_file).
OTOOH this function is only called by find_main_filename.

So what to do?

I'm tempted to rename the routine {,*_}find_function_file (or some
such) and have dw2_find_symbol_file ignore TUs.