[PATCH v2 5/5] ld: clarify comments on /DISCARD/ output section behavior

[Jan Beulich]

On 17.10.2025 17:01, Matthieu Longo wrote:
> On 2025-10-16 07:42, Jan Beulich wrote:
>> On 15.10.2025 17:53, Matthieu Longo wrote:
>>> On 2025-10-15 14:13, Jan Beulich wrote:
>>>> On 14.10.2025 12:46, Matthieu Longo wrote:
>>>>> --- a/ld/ldlang.c
>>>>> +++ b/ld/ldlang.c
>>>>> @@ -2709,17 +2709,25 @@ wont_add_section_p (asection *section,
>>>>>         if (discard)
>>>>>        {
>>>>> +      /* /DISCARD/ is seen first and the top-most clause has precedence on the
>>>>> +     next ones, thus the section will be dropped.  No need to warn about
>>>>> +     potential change in behavior with non-contiguous regions when the
>>>>> +     section is already dropped.  */
>>>>>          if (section->output_section == NULL)
>>>>>        {
>>>>>          /* This prevents future calls from assigning this section or
>>>>>             warning about it again.  */
>>>>>          section->output_section = bfd_abs_section_ptr;
>>>>>        }
>>>>> -      else if (bfd_is_abs_section (section->output_section))
>>>>> -    ;
>>>>> -      else if (link_info.non_contiguous_regions_warnings)
>>>>> +      /* The /DISCARD/ clause appears after previous ones which assigned the
>>>>> +     input section to an output section.  /DISCARD/ does not have the
>>>>> +     precedence, so the section will be kept.  */
>>>>> +      else if (! bfd_is_abs_section (section->output_section)
>>>>> +           && link_info.non_contiguous_regions_warnings)
>>>>>        einfo (_("%P:%pS: warning: --enable-non-contiguous-regions makes "
>>>>> -         "section `%pA' from `%pB' match /DISCARD/ clause.\n"),
>>>>> +         "section `%pA' from `%pB' match /DISCARD/ clause.  If the "
>>>>> +         "section can be assigned to an output section, it won't be "
>>>>> +         "discarded.\n"),
>>>>
>>>> Besides this getting excessively long for a single line, to me comment and
>>>> message text also read partially contradictory: The comment says "will",
>>>> while the diagnostic effectively says "may". Which one is it?
>>>
>>> If I understood you well, you say that the diagnostic message
>>> contradicts the following explanation from the commit message:
>>>   > - If /DISCARD/ follows clauses that assign the input section to an output
>>>   >   section, /DISCARD/ is ignored, and the section is kept. In this case,
>>>   >   the linker must warn that the section *may* not be discarded.
>>
>> No, my remark was about the code comment (see context above). Still ...
>>
> 
> What about this ? Is it clearer ?

Yes, thanks (and okay with this adjustment).

Jan

> +      /* The /DISCARD/ clause follows clauses that assign the input section to
> +        an output section. Since /DISCARD/ does not have the precedence,
> +        /DISCARD/ is ignored.
> +        1. If the input section can be assigned to an output section,
> +           the link will succeed. The warning below is emitted with
> +           --enable-non-contiguous-regions-warnings so that the user can
> +           notice that /DISCARD/ did not do what he might have expected,
> +           i.e. discarding the input section.
> +        2. If the input section cannot be assigned, the link will fail
> +           with an error. The warning below is emitted with
> +           --enable-non-contiguous-regions-warnings so that the user can
> +           notice that /DISCARD/ was ignored for this input section, then
> +           leading to a link failure caused by not enough space in the output
> +           section for the input section.  */
> +      else if (! bfd_is_abs_section (section->output_section)
> +              && link_info.non_contiguous_regions_warnings)