[PATCH 1/3] ld/ELF: Move -z dynamic-undefined-weak flag handling to elf.em

[hakan]

>> diff --git a/ld/lexsup.c b/ld/lexsup.c
>> index bde20465835..5f0c040e352 100644
>> --- a/ld/lexsup.c
>> +++ b/ld/lexsup.c
>> @@ -2267,6 +2267,9 @@ elf_shlib_list_options (FILE *file)
>>    fprintf (file, _("\
>>    -z nomemory-seal            Don't mark oject to be memory sealed (default)\n"));
>>  #endif
>> +  fprintf (file, _("\
>> +  -z dynamic-undefined-weak   Make undefined weak symbols dynamic\n\
>> +  -z nodynamic-undefined-weak Do not make undefined weak symbols dynamic\n"));
>
>Please add "(default)" to the default option.
>

Hi H.J.,

Thanks for the review.

To clarify: neither `-z dynamic-undefined-weak` nor `-z
nodynamic-undefined-weak` is the default. The default behavior is
backend-specific. Unless either flag is passed, no elflink-level
decision is made. This can be seen in `bfd/elflink.c`, function
`_bfd_elf_adjust_dynamic_symbol`:

 3252   if (h->root.type == bfd_link_hash_undefweak) // this part gets changed in the following commit
 3253     {
 3254       if (eif->info->dynamic_undefined_weak == 0)
 3255         (*bed->elf_backend_hide_symbol) (eif->info, h, true);
 3256       else if (eif->info->dynamic_undefined_weak > 0
 3257                && h->ref_regular
 3258                && ELF_ST_VISIBILITY (h->other) == STV_DEFAULT
 3259                && !bfd_hide_sym_by_version (eif->info->version_info,
 3260                                             h->root.root.string))
 3261         {
 3262           if (!bfd_elf_link_record_dynamic_symbol (eif->info, h))
 3263             {
 3264               eif->failed = true;
 3265               return false;
 3266             }
 3267         }
 3268     }

The default value of `link_info.dynamic_undefined_weak` is -1, so
neither the hide path (line 3255) nor the dynamic promotion path
(lines 3256-3267) is executed.

Each backend currently implements its own undefined symbol promotion
logic (often retaining undefweaks) in `elf_<backend>_allocate_dynrelocs`.
However, that can be overriden by elflink in the above function, if flag
was passed.

Thoughts? Should we standardize on one of the two as the default,
or preserve current backend-specific behavior?

Best regards,
Hakan