[PATCH] DWARF5: Don't generate DW_AT_loclists_base for split compile unit DIEs.

[Mark Wielaard]

On Sat, 2018-05-26 at 21:31 +0200, Mark Wielaard wrote:
> The loclists_base attribute is used to point to the beginning of the
> loclists index of a DWARF5 loclists table when using DW_FORM_loclistsx.
> For split compile units the base is not given by the attribute, but is
> either the first (and only) index in the .debug_loclists.dwo section,
> or (when placed in a .dwp file) given by the DW_SECT_LOCLISTS row in
> the .debug_cu_index section.
> 
> The loclists_base attribute is only valid for the full (or skeleton)
> compile unit DIE in the main (relocatable) object. But GCC only ever
> generates a loclists table index for the .debug_loclists section put
> into the split DWARF .dwo file.
> 
> For split compile unit DIEs it is confusing (and not according to spec)
> to also have a DW_AT_loclists_base attribute (which might be wrong,
> since its relocatable offset won't actually be relocated).

Ping.

> gcc/ChangeLog
> 
> 	* dwarf2out.c (dwarf2out_finish): Remove generation of
> 	DW_AT_loclists_base.
> ---
> 
> diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
> index c05bfe4..103ded0 100644
> --- a/gcc/dwarf2out.c
> +++ b/gcc/dwarf2out.c
> @@ -31292,11 +31292,17 @@ dwarf2out_finish (const char *)
>    if (dwarf_split_debug_info)
>      {
>        if (have_location_lists)
> >  	{
> > -	  if (dwarf_version >= 5)
> > -	    add_AT_loclistsptr (comp_unit_die (), DW_AT_loclists_base,
> > -				loc_section_label);
> > +	  /* Since we generate the loclists in the split DWARF .dwo
> > +	     file itself, we don't need to generate a loclists_base
> > +	     attribute for the split compile unit DIE.  That attribute
> > +	     (and using relocatable sec_offset FORMs) isn't allowed
> > +	     for a split compile unit.  Only if the .debug_loclists
> > +	     section was in the main file, would we need to generate a
> > +	     loclists_base attribute here (for the full or skeleton
> > +	     unit DIE).  */
> +
> >  	  /* optimize_location_lists calculates the size of the lists,
> >  	     so index them first, and assign indices to the entries.
> >  	     Although optimize_location_lists will remove entries from
> >  	     the table, it only does so for duplicates, and therefore