[PATCH v9 06/19] bfd: write Object Attributes v2

[Matthieu Longo]

On 07/11/2025 08:23, Jan Beulich wrote:
> On 05.11.2025 11:18, Matthieu Longo wrote:
>> On 30/10/2025 15:55, Jan Beulich wrote:
>>> On 01.09.2025 18:56, Matthieu Longo wrote:
>>>> --- a/gas/write.c
>>>> +++ b/gas/write.c
>>>> @@ -1919,6 +1919,8 @@ create_obj_attrs_section (void)
>>>>      bfd_set_section_flags (s, SEC_READONLY | SEC_DATA);
>>>>      frag_now_fix ();
>>>>      char *p = frag_more (size);
>>>> +
>>>> +  bfd_elf_obj_attr_finalize_contents (stdoutput);
>>>>      bfd_elf_set_obj_attr_contents (stdoutput, (bfd_byte *)p, size);
>>>
>>> Why is another export needed from libbfd? Can't bfd_elf_set_obj_attr_contents()
>>> simply do whatever it takes? The other caller likely needs doing the same anyway?
>>
>> bfd_elf_set_obj_attr_contents() is also used in objcpy, and objcpy
>> should not change the order of subsections and attributes, but simply
>> make a copy of the data as they were in the original object.
> 
> Is this the case already prior to your series? I can't seem to be able to
> identify the call path for that case. Besides the direct call from gas,
> bfd_elf_set_obj_attr_contents() is called only from
> _bfd_elf_write_section_build_attributes(), which in turn is called solely by
> bfd_elf_final_link(). And I can't see this being used by objcopy.
> 

Sorry, I said something wrong. It is not used for objcopy but by the 
linker in _bfd_elf_write_section_object_attributes().

In the case of the link, all the subsections and attributes are already 
sorted by the merge, so no need to sort them again.

>> Another possibility might be to add a parameter to
>> bfd_elf_set_obj_attr_contents() to enable/disable the sorting.
> 
> Can the distinction not be made by what struct bfd_link_info contains?
> 
> Jan

Here is the new approach after having eliminated 
bfd_elf_obj_attr_finalize_contents(). It relies on is_linker_output 
being set to 1 in the case of the linker. Is it the approach that you 
had in mind ?

/* Write the contents of the object attributes section to CONTENTS.  */
void
bfd_elf_set_obj_attr_contents (bfd *abfd, bfd_byte *buffer, bfd_vma size)
{
   if ((! abfd->is_linker_output)
       && elf_obj_attr_version (abfd) == OBJ_ATTR_V2)
     /* Before dumping the data, sort subsections in alphabetical order, and
        attributes according to their tag in numerical order.  This is 
useful
        for diagnostic tools so that they dump the same output even if the
        subsections or their attributes were not declared in the same 
order in
        different files.
        This sorting is only performed in the case of the assembler.  In the
        case of the linker, the subsections and attributes are already 
sorted
        by the merge process.  */
     oav2_sort_subsections (&elf_obj_attr_subsections (abfd));

   obj_attr_version_t version = elf_obj_attr_version (abfd);
   if (version == OBJ_ATTR_V1)
     oav1_write_section (abfd, buffer, size);
   else if (version == OBJ_ATTR_V2)
     oav2_write_section (abfd, buffer, size);
   else
     abort ();
}

Matthieu