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

[Jason Merrill <jason at redhat dot com>]

OK.

On Fri, Jun 1, 2018 at 8:29 AM, Mark Wielaard <mark@klomp.org> wrote:
> 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