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

[Jan Beulich]

On 01.09.2025 18:56, Matthieu Longo wrote:
> --- a/bfd/elf-attrs.c
> +++ b/bfd/elf-attrs.c
> @@ -131,13 +131,61 @@ vendor_obj_attrs_v1_size (bfd *abfd, int vendor)
>  }
>  
>  static bfd_vma
> -bfd_elf_obj_attrs_v1_size (bfd *abfd)
> +oav1_section_size (bfd *abfd)
>  {
>    bfd_vma size = 0;
>    size = vendor_obj_attrs_v1_size (abfd, OBJ_ATTR_PROC);
>    size += vendor_obj_attrs_v1_size (abfd, OBJ_ATTR_GNU);
>    if (size > 0)
> -    size += sizeof(uint8_t); /* <format-version: ‘A’>  */
> +    size += sizeof (uint8_t); /* <format-version: uint8>  */
> +  return size;
> +}
> +
> +/* Return the size of a single attribute.  */
> +static bfd_vma
> +oav2_attr_size (const obj_attr_v2 *attr, obj_attr_encoding_v2 type)

With the const here, ...

> +{
> +  bfd_vma size = uleb128_size (attr->tag);
> +  switch (type)
> +    {
> +    case OA_ENC_ULEB128:
> +      size += uleb128_size (attr->val.uint_val);
> +      break;
> +    case OA_ENC_NTBS:
> +      size += strlen (attr->val.string_val) + 1; /* +1 for '\0'.  */
> +      break;
> +    default:
> +      abort ();
> +    }
> +  return size;
> +}
> +
> +/* Return the size of a subsection.  */
> +static bfd_vma
> +oav2_subsection_size (const obj_attr_subsection_v2 *subsec)
> +{
> +  bfd_vma size = sizeof (uint32_t); /* <subsection-length: uint32>  */
> +  size += strlen (subsec->name) + 1; /* <subsection-name: NTBS>  so +1 for '\0'.  */
> +  size += 2 * sizeof (uint8_t); /* <optional: uint8> <encoding: uint8>  */
> +  /* <attribute>*  */
> +  for (obj_attr_v2 *attr = subsec->first;

... please also use it e.g. here.

> +       attr != NULL;
> +       attr = attr->next)
> +    size += oav2_attr_size (attr, subsec->encoding);
> +  return size;
> +}
> +
> +/* Return the size of a build attributes section.  */
> +static bfd_vma
> +oav2_section_size (bfd *abfd)
> +{
> +  const obj_attr_subsection_v2 *subsec = elf_obj_attr_subsections (abfd).first;
> +  if (subsec == NULL)
> +    return 0;
> +
> +  bfd_vma size = sizeof (uint8_t); /* <format-version: uint8>  */
> +  for (; subsec != NULL; subsec = subsec->next)
> +    size += oav2_subsection_size (subsec);
>    return size;
>  }
>  
> @@ -145,7 +193,15 @@ bfd_elf_obj_attrs_v1_size (bfd *abfd)
>  bfd_vma
>  bfd_elf_obj_attr_size (bfd *abfd)
>  {
> -  return bfd_elf_obj_attrs_v1_size (abfd);
> +  obj_attr_version_t version = elf_obj_attr_version (abfd);
> +  if (version == OBJ_ATTR_V1)
> +    return oav1_section_size (abfd);
> +  else if (version == OBJ_ATTR_V2)
> +    return oav2_section_size (abfd);
> +  else if (version == OBJ_ATTR_VERSION_NONE)
> +    return 0;
> +  else
> +    abort ();
>  }

Better use switch() in such a case?

> @@ -227,8 +283,8 @@ write_vendor_obj_attrs_v1 (bfd *abfd, bfd_byte *contents, bfd_vma size,
>      p = write_obj_attr_v1 (p, list->tag, &list->attr);
>  }
>  
> -static void
> -write_obj_attr_section_v1 (bfd *abfd, bfd_byte *buffer, bfd_vma size)
> +static bfd_vma
> +oav1_write_section (bfd *abfd, bfd_byte *buffer, bfd_vma size)
>  {
>    bfd_byte *p = buffer;

Why the change in return type? The sole caller doesn't use the new return value.

> @@ -246,13 +302,126 @@ write_obj_attr_section_v1 (bfd *abfd, bfd_byte *buffer, bfd_vma size)
>  
>    /* We didn't overrun the buffer.  */
>    BFD_ASSERT (p <= buffer + size);
> +  return p - buffer;
> +}
> +
> +static bfd_byte *
> +oav2_write_attr (bfd_byte *p,
> +		 const obj_attr_v2 *attr,
> +		 obj_attr_encoding_v2 type)
> +{
> +  p = write_uleb128 (p, attr->tag);
> +  switch (type)
> +    {
> +    case OA_ENC_ULEB128:
> +      p = write_uleb128 (p, attr->val.uint_val);
> +      break;
> +    case OA_ENC_NTBS:
> +      {
> +	size_t len = strlen (attr->val.string_val) + 1; /* +1 for '\0'.  */
> +	memcpy (p, attr->val.string_val, len);
> +	p += len;

	p = stpcpy (p, attr->val.string_val) + 1;

?

> +static bfd_byte *
> +oav2_write_subsection (bfd *abfd,
> +		       const obj_attr_subsection_v2 *subsec,
> +		       bfd_byte *p)
> +{
> +  /* <subsection-length: uint32>  */
> +  bfd_vma subsec_size = oav2_subsection_size (subsec);
> +  bfd_put_32 (abfd, subsec_size, p);
> +  p += sizeof (uint32_t);
> +
> +  /* <vendor-name: NTBS>  */
> +  size_t vendor_name_size = strlen (subsec->name) + 1; /* +1 for '\0'.  */
> +  memcpy (p, subsec->name, vendor_name_size);
> +  p += vendor_name_size;
> +
> +  /* -- <vendor-data: bytes> --  */
> +  /* <optional: uint8>  */
> +  bfd_put_8 (abfd, subsec->optional, p);
> +  ++p;
> +  /* <encoding: uint8>  */
> +  bfd_put_8 (abfd, obj_attr_encoding_v2_to_u8 (subsec->encoding), p);
> +  ++p;
> +  /* <attribute>*  */
> +  for (obj_attr_v2 *attr = subsec->first; attr != NULL; attr = attr->next)

Again - const here (and potentially elsewhere) as well please.

> @@ -1006,7 +1175,7 @@ _bfd_elf_merge_unknown_attribute_list (bfd *ibfd, bfd *obfd)
>    return result;
>  }
>  
> -/* Create a new object attribute with key TAG and value VALS.
> +/* Create a new object attribute with key TAG and value VAL.
>     Return a pointer to it.  */

Likely belongs in an earlier patch?

> --- 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?

Jan