[PATCH v1 5/5] ld: clarify comments on /DISCARD/ output section behavior

[Matthieu Longo]

On 2025-09-26 14:19, Jan Beulich wrote:
> On 18.09.2025 17:06, Matthieu Longo wrote:
>> The previous comments made it difficult to understand how the /DISCARD/
>> output section interacts with non-contiguous regions.
>>
>> In summary, the general rule is that the first (top-most) clause takes
>> precedence over subsequent ones:
>> - If /DISCARD/ appears first, the section is dropped. There is no need
>>    to warn about potential behavior changes with non-contiguous regions
>>    when the section is already discarded.
>> - 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.
> 
> Looks okay to me, just that again ...
> 
>> --- a/ld/ldlang.c
>> +++ b/ld/ldlang.c
>> @@ -2709,18 +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"),
>> -	       NULL, section, section->owner);
>> +		 "section `%pA' from `%pB' match /DISCARD/ clause.  If the "
>> +		 "section can be assigned to an output section, it won't be "
>> +		 "discarded.\n"), NULL, section, section->owner);
> 
> ... original line splitting style wants retaining here.
> 
> Jan


Fixed in the next revision.

Matthieu