Re: [PATCH 4/8] Avoid shadowing in linux-tdep.c

[Kevin Buettner <kevinb@redhat.com>]

On Sat, 22 Sep 2018 22:08:10 -0600
Tom Tromey <tom@tromey.com> wrote:

> This is one of the uglier changes to avoid local shadowing.  Because
> obstack.h uses statement expressions, in some cases a nested obstack
> call will result in shadowing.  Rather than try to fix obstack.h, this
> patch simply works around the one instance of this problem.
> 
> gdb/ChangeLog
> 2018-09-22  Tom Tromey  <tom@tromey.com>
> 
> 	* linux-tdep.c (linux_make_mappings_corefile_notes): Introduce new
> 	variable "size".
> ---
>  gdb/ChangeLog    | 5 +++++
>  gdb/linux-tdep.c | 3 ++-
>  2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/gdb/linux-tdep.c b/gdb/linux-tdep.c
> index 8c76ec316b..352114943f 100644
> --- a/gdb/linux-tdep.c
> +++ b/gdb/linux-tdep.c
> @@ -1547,8 +1547,9 @@ linux_make_mappings_corefile_notes (struct gdbarch *gdbarch, bfd *obfd,
>  		 long_type, mapping_data.file_count);
>  
>        /* Copy the filenames to the data obstack.  */
> +      int size = obstack_object_size (&filename_obstack);
>        obstack_grow (&data_obstack, obstack_base (&filename_obstack),
> -		    obstack_object_size (&filename_obstack));
> +		    size);
>  
>        note_data = elfcore_write_note (obfd, note_data, note_size,
>  				      "CORE", NT_FILE,
> -- 
> 2.17.1

It took me a while to understand this one.  IIUC, the problem is that __o
in obstack_object_size will shadow __o in obstack_grow.

Yeah, this is ugly.  But I can't think of a better way to fix it short
of mucking about in obstack.h.

My only suggestion is to add a brief comment on the matter so that
someone else doesn't rewrite this code back to the way it was before
this patch.  Otherwise, LGTM.

Kevin