Home | History | Annotate | Download | only in bfd
      1 /* ELF attributes support (based on ARM EABI attributes).
      2    Copyright (C) 2005-2016 Free Software Foundation, Inc.
      3 
      4    This file is part of BFD, the Binary File Descriptor library.
      5 
      6    This program is free software; you can redistribute it and/or modify
      7    it under the terms of the GNU General Public License as published by
      8    the Free Software Foundation; either version 3 of the License, or
      9    (at your option) any later version.
     10 
     11    This program is distributed in the hope that it will be useful,
     12    but WITHOUT ANY WARRANTY; without even the implied warranty of
     13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     14    GNU General Public License for more details.
     15 
     16    You should have received a copy of the GNU General Public License
     17    along with this program; if not, write to the Free Software
     18    Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
     19    MA 02110-1301, USA.  */
     20 
     21 #include "sysdep.h"
     22 #include "bfd.h"
     23 #include "libiberty.h"
     24 #include "libbfd.h"
     25 #include "elf-bfd.h"
     26 
     27 /* Return the number of bytes needed by I in uleb128 format.  */
     28 static int
     29 uleb128_size (unsigned int i)
     30 {
     31   int size;
     32   size = 1;
     33   while (i >= 0x80)
     34     {
     35       i >>= 7;
     36       size++;
     37     }
     38   return size;
     39 }
     40 
     41 /* Return TRUE if the attribute has the default value (0/"").  */
     42 static bfd_boolean
     43 is_default_attr (obj_attribute *attr)
     44 {
     45   if (ATTR_TYPE_HAS_INT_VAL (attr->type) && attr->i != 0)
     46     return FALSE;
     47   if (ATTR_TYPE_HAS_STR_VAL (attr->type) && attr->s && *attr->s)
     48     return FALSE;
     49   if (ATTR_TYPE_HAS_NO_DEFAULT (attr->type))
     50     return FALSE;
     51 
     52   return TRUE;
     53 }
     54 
     55 /* Return the size of a single attribute.  */
     56 static bfd_vma
     57 obj_attr_size (unsigned int tag, obj_attribute *attr)
     58 {
     59   bfd_vma size;
     60 
     61   if (is_default_attr (attr))
     62     return 0;
     63 
     64   size = uleb128_size (tag);
     65   if (ATTR_TYPE_HAS_INT_VAL (attr->type))
     66     size += uleb128_size (attr->i);
     67   if (ATTR_TYPE_HAS_STR_VAL (attr->type))
     68     size += strlen ((char *)attr->s) + 1;
     69   return size;
     70 }
     71 
     72 /* Return the vendor name for a given object attributes section.  */
     73 static const char *
     74 vendor_obj_attr_name (bfd *abfd, int vendor)
     75 {
     76   return (vendor == OBJ_ATTR_PROC
     77 	  ? get_elf_backend_data (abfd)->obj_attrs_vendor
     78 	  : "gnu");
     79 }
     80 
     81 /* Return the size of the object attributes section for VENDOR
     82    (OBJ_ATTR_PROC or OBJ_ATTR_GNU), or 0 if there are no attributes
     83    for that vendor to record and the vendor is OBJ_ATTR_GNU.  */
     84 static bfd_vma
     85 vendor_obj_attr_size (bfd *abfd, int vendor)
     86 {
     87   bfd_vma size;
     88   obj_attribute *attr;
     89   obj_attribute_list *list;
     90   int i;
     91   const char *vendor_name = vendor_obj_attr_name (abfd, vendor);
     92 
     93   if (!vendor_name)
     94     return 0;
     95 
     96   attr = elf_known_obj_attributes (abfd)[vendor];
     97   size = 0;
     98   for (i = LEAST_KNOWN_OBJ_ATTRIBUTE; i < NUM_KNOWN_OBJ_ATTRIBUTES; i++)
     99     size += obj_attr_size (i, &attr[i]);
    100 
    101   for (list = elf_other_obj_attributes (abfd)[vendor];
    102        list;
    103        list = list->next)
    104     size += obj_attr_size (list->tag, &list->attr);
    105 
    106   /* <size> <vendor_name> NUL 0x1 <size> */
    107   return ((size || vendor == OBJ_ATTR_PROC)
    108 	  ? size + 10 + strlen (vendor_name)
    109 	  : 0);
    110 }
    111 
    112 /* Return the size of the object attributes section.  */
    113 bfd_vma
    114 bfd_elf_obj_attr_size (bfd *abfd)
    115 {
    116   bfd_vma size;
    117 
    118   size = vendor_obj_attr_size (abfd, OBJ_ATTR_PROC);
    119   size += vendor_obj_attr_size (abfd, OBJ_ATTR_GNU);
    120 
    121   /* 'A' <sections for each vendor> */
    122   return (size ? size + 1 : 0);
    123 }
    124 
    125 /* Write VAL in uleb128 format to P, returning a pointer to the
    126    following byte.  */
    127 static bfd_byte *
    128 write_uleb128 (bfd_byte *p, unsigned int val)
    129 {
    130   bfd_byte c;
    131   do
    132     {
    133       c = val & 0x7f;
    134       val >>= 7;
    135       if (val)
    136 	c |= 0x80;
    137       *(p++) = c;
    138     }
    139   while (val);
    140   return p;
    141 }
    142 
    143 /* Write attribute ATTR to butter P, and return a pointer to the following
    144    byte.  */
    145 static bfd_byte *
    146 write_obj_attribute (bfd_byte *p, unsigned int tag, obj_attribute *attr)
    147 {
    148   /* Suppress default entries.  */
    149   if (is_default_attr (attr))
    150     return p;
    151 
    152   p = write_uleb128 (p, tag);
    153   if (ATTR_TYPE_HAS_INT_VAL (attr->type))
    154     p = write_uleb128 (p, attr->i);
    155   if (ATTR_TYPE_HAS_STR_VAL (attr->type))
    156     {
    157       int len;
    158 
    159       len = strlen (attr->s) + 1;
    160       memcpy (p, attr->s, len);
    161       p += len;
    162     }
    163 
    164   return p;
    165 }
    166 
    167 /* Write the contents of the object attributes section (length SIZE)
    168    for VENDOR to CONTENTS.  */
    169 static void
    170 vendor_set_obj_attr_contents (bfd *abfd, bfd_byte *contents, bfd_vma size,
    171 			      int vendor)
    172 {
    173   bfd_byte *p;
    174   obj_attribute *attr;
    175   obj_attribute_list *list;
    176   int i;
    177   const char *vendor_name = vendor_obj_attr_name (abfd, vendor);
    178   size_t vendor_length = strlen (vendor_name) + 1;
    179 
    180   p = contents;
    181   bfd_put_32 (abfd, size, p);
    182   p += 4;
    183   memcpy (p, vendor_name, vendor_length);
    184   p += vendor_length;
    185   *(p++) = Tag_File;
    186   bfd_put_32 (abfd, size - 4 - vendor_length, p);
    187   p += 4;
    188 
    189   attr = elf_known_obj_attributes (abfd)[vendor];
    190   for (i = LEAST_KNOWN_OBJ_ATTRIBUTE; i < NUM_KNOWN_OBJ_ATTRIBUTES; i++)
    191     {
    192       unsigned int tag = i;
    193       if (get_elf_backend_data (abfd)->obj_attrs_order)
    194 	tag = get_elf_backend_data (abfd)->obj_attrs_order (i);
    195       p = write_obj_attribute (p, tag, &attr[tag]);
    196     }
    197 
    198   for (list = elf_other_obj_attributes (abfd)[vendor];
    199        list;
    200        list = list->next)
    201     p = write_obj_attribute (p, list->tag, &list->attr);
    202 }
    203 
    204 /* Write the contents of the object attributes section to CONTENTS.  */
    205 void
    206 bfd_elf_set_obj_attr_contents (bfd *abfd, bfd_byte *contents, bfd_vma size)
    207 {
    208   bfd_byte *p;
    209   int vendor;
    210   bfd_vma my_size;
    211 
    212   p = contents;
    213   *(p++) = 'A';
    214   my_size = 1;
    215   for (vendor = OBJ_ATTR_FIRST; vendor <= OBJ_ATTR_LAST; vendor++)
    216     {
    217       bfd_vma vendor_size = vendor_obj_attr_size (abfd, vendor);
    218       if (vendor_size)
    219 	vendor_set_obj_attr_contents (abfd, p, vendor_size, vendor);
    220       p += vendor_size;
    221       my_size += vendor_size;
    222     }
    223 
    224   if (size != my_size)
    225     abort ();
    226 }
    227 
    228 /* Allocate/find an object attribute.  */
    229 static obj_attribute *
    230 elf_new_obj_attr (bfd *abfd, int vendor, unsigned int tag)
    231 {
    232   obj_attribute *attr;
    233   obj_attribute_list *list;
    234   obj_attribute_list *p;
    235   obj_attribute_list **lastp;
    236 
    237 
    238   if (tag < NUM_KNOWN_OBJ_ATTRIBUTES)
    239     {
    240       /* Known tags are preallocated.  */
    241       attr = &elf_known_obj_attributes (abfd)[vendor][tag];
    242     }
    243   else
    244     {
    245       /* Create a new tag.  */
    246       list = (obj_attribute_list *)
    247 	bfd_alloc (abfd, sizeof (obj_attribute_list));
    248       memset (list, 0, sizeof (obj_attribute_list));
    249       list->tag = tag;
    250       /* Keep the tag list in order.  */
    251       lastp = &elf_other_obj_attributes (abfd)[vendor];
    252       for (p = *lastp; p; p = p->next)
    253 	{
    254 	  if (tag < p->tag)
    255 	    break;
    256 	  lastp = &p->next;
    257 	}
    258       list->next = *lastp;
    259       *lastp = list;
    260       attr = &list->attr;
    261     }
    262 
    263   return attr;
    264 }
    265 
    266 /* Return the value of an integer object attribute.  */
    267 int
    268 bfd_elf_get_obj_attr_int (bfd *abfd, int vendor, unsigned int tag)
    269 {
    270   obj_attribute_list *p;
    271 
    272   if (tag < NUM_KNOWN_OBJ_ATTRIBUTES)
    273     {
    274       /* Known tags are preallocated.  */
    275       return elf_known_obj_attributes (abfd)[vendor][tag].i;
    276     }
    277   else
    278     {
    279       for (p = elf_other_obj_attributes (abfd)[vendor];
    280 	   p;
    281 	   p = p->next)
    282 	{
    283 	  if (tag == p->tag)
    284 	    return p->attr.i;
    285 	  if (tag < p->tag)
    286 	    break;
    287 	}
    288       return 0;
    289     }
    290 }
    291 
    292 /* Add an integer object attribute.  */
    293 void
    294 bfd_elf_add_obj_attr_int (bfd *abfd, int vendor, unsigned int tag, unsigned int i)
    295 {
    296   obj_attribute *attr;
    297 
    298   attr = elf_new_obj_attr (abfd, vendor, tag);
    299   attr->type = _bfd_elf_obj_attrs_arg_type (abfd, vendor, tag) | ATTR_TYPE_FLAG_EXIST;
    300   attr->i = i;
    301 }
    302 
    303 /* Duplicate an object attribute string value.  */
    304 char *
    305 _bfd_elf_attr_strdup (bfd *abfd, const char * s)
    306 {
    307   char * p;
    308   int len;
    309 
    310   len = strlen (s) + 1;
    311   p = (char *) bfd_alloc (abfd, len);
    312   return (char *) memcpy (p, s, len);
    313 }
    314 
    315 /* Add a string object attribute.  */
    316 void
    317 bfd_elf_add_obj_attr_string (bfd *abfd, int vendor, unsigned int tag, const char *s)
    318 {
    319   obj_attribute *attr;
    320 
    321   attr = elf_new_obj_attr (abfd, vendor, tag);
    322   attr->type = _bfd_elf_obj_attrs_arg_type (abfd, vendor, tag) | ATTR_TYPE_FLAG_EXIST;
    323   attr->s = _bfd_elf_attr_strdup (abfd, s);
    324 }
    325 
    326 /* Add a int+string object attribute.  */
    327 void
    328 bfd_elf_add_obj_attr_int_string (bfd *abfd, int vendor,
    329 				 unsigned int tag,
    330 				 unsigned int i, const char *s)
    331 {
    332   obj_attribute *attr;
    333 
    334   attr = elf_new_obj_attr (abfd, vendor, tag);
    335   attr->type = _bfd_elf_obj_attrs_arg_type (abfd, vendor, tag) | ATTR_TYPE_FLAG_EXIST;
    336   attr->i = i;
    337   attr->s = _bfd_elf_attr_strdup (abfd, s);
    338 }
    339 
    340 /* Copy the object attributes from IBFD to OBFD.  */
    341 void
    342 _bfd_elf_copy_obj_attributes (bfd *ibfd, bfd *obfd)
    343 {
    344   obj_attribute *in_attr;
    345   obj_attribute *out_attr;
    346   obj_attribute_list *list;
    347   int i;
    348   int vendor;
    349 
    350   if (bfd_get_flavour (ibfd) != bfd_target_elf_flavour
    351       || bfd_get_flavour (obfd) != bfd_target_elf_flavour)
    352     return;
    353 
    354   for (vendor = OBJ_ATTR_FIRST; vendor <= OBJ_ATTR_LAST; vendor++)
    355     {
    356       in_attr
    357 	= &elf_known_obj_attributes (ibfd)[vendor][LEAST_KNOWN_OBJ_ATTRIBUTE];
    358       out_attr
    359 	= &elf_known_obj_attributes (obfd)[vendor][LEAST_KNOWN_OBJ_ATTRIBUTE];
    360       for (i = LEAST_KNOWN_OBJ_ATTRIBUTE; i < NUM_KNOWN_OBJ_ATTRIBUTES; i++)
    361 	{
    362 	  out_attr->type = in_attr->type;
    363 	  out_attr->i = in_attr->i;
    364 	  if (in_attr->s && *in_attr->s)
    365 	    out_attr->s = _bfd_elf_attr_strdup (obfd, in_attr->s);
    366 	  in_attr++;
    367 	  out_attr++;
    368 	}
    369 
    370       for (list = elf_other_obj_attributes (ibfd)[vendor];
    371 	   list;
    372 	   list = list->next)
    373 	{
    374 	  in_attr = &list->attr;
    375 	  switch (in_attr->type & (ATTR_TYPE_FLAG_INT_VAL | ATTR_TYPE_FLAG_STR_VAL))
    376 	    {
    377 	    case ATTR_TYPE_FLAG_INT_VAL:
    378 	      bfd_elf_add_obj_attr_int (obfd, vendor, list->tag, in_attr->i);
    379 	      break;
    380 	    case ATTR_TYPE_FLAG_STR_VAL:
    381 	      bfd_elf_add_obj_attr_string (obfd, vendor, list->tag,
    382 					   in_attr->s);
    383 	      break;
    384 	    case ATTR_TYPE_FLAG_INT_VAL | ATTR_TYPE_FLAG_STR_VAL:
    385 	      bfd_elf_add_obj_attr_int_string (obfd, vendor, list->tag,
    386 					       in_attr->i, in_attr->s);
    387 	      break;
    388 	    default:
    389 	      abort ();
    390 	    }
    391 	}
    392     }
    393 }
    394 
    395 /* Determine whether a GNU object attribute tag takes an integer, a
    396    string or both.  */
    397 static int
    398 gnu_obj_attrs_arg_type (unsigned int tag)
    399 {
    400   /* Except for Tag_compatibility, for GNU attributes we follow the
    401      same rule ARM ones > 32 follow: odd-numbered tags take strings
    402      and even-numbered tags take integers.  In addition, tag & 2 is
    403      nonzero for architecture-independent tags and zero for
    404      architecture-dependent ones.  */
    405   if (tag == Tag_compatibility)
    406     return 3;
    407   else
    408     return (tag & 1) != 0 ? 2 : 1;
    409 }
    410 
    411 /* Determine what arguments an attribute tag takes.  */
    412 int
    413 _bfd_elf_obj_attrs_arg_type (bfd *abfd, int vendor, unsigned int tag)
    414 {
    415   switch (vendor)
    416     {
    417     case OBJ_ATTR_PROC:
    418       return get_elf_backend_data (abfd)->obj_attrs_arg_type (tag);
    419       break;
    420     case OBJ_ATTR_GNU:
    421       return gnu_obj_attrs_arg_type (tag);
    422       break;
    423     default:
    424       abort ();
    425     }
    426 }
    427 
    428 /* Parse an object attributes section.  */
    429 void
    430 _bfd_elf_parse_attributes (bfd *abfd, Elf_Internal_Shdr * hdr)
    431 {
    432   bfd_byte *contents;
    433   bfd_byte *p;
    434   bfd_byte *p_end;
    435   bfd_vma len;
    436   const char *std_sec;
    437 
    438   /* PR 17512: file: 2844a11d.  */
    439   if (hdr->sh_size == 0)
    440     return;
    441   contents = (bfd_byte *) bfd_malloc (hdr->sh_size);
    442   if (!contents)
    443     return;
    444   if (!bfd_get_section_contents (abfd, hdr->bfd_section, contents, 0,
    445 				 hdr->sh_size))
    446     {
    447       free (contents);
    448       return;
    449     }
    450   p = contents;
    451   p_end = p + hdr->sh_size;
    452   std_sec = get_elf_backend_data (abfd)->obj_attrs_vendor;
    453 
    454   if (*(p++) == 'A')
    455     {
    456       len = hdr->sh_size - 1;
    457 
    458       while (len > 0 && p < p_end - 4)
    459 	{
    460 	  unsigned namelen;
    461 	  bfd_vma section_len;
    462 	  int vendor;
    463 
    464 	  section_len = bfd_get_32 (abfd, p);
    465 	  p += 4;
    466 	  if (section_len == 0)
    467 	    break;
    468 	  if (section_len > len)
    469 	    section_len = len;
    470 	  len -= section_len;
    471 	  section_len -= 4;
    472 	  namelen = strnlen ((char *) p, section_len) + 1;
    473 	  if (namelen == 0 || namelen >= section_len)
    474 	    break;
    475 	  section_len -= namelen;
    476 	  if (std_sec && strcmp ((char *) p, std_sec) == 0)
    477 	    vendor = OBJ_ATTR_PROC;
    478 	  else if (strcmp ((char *) p, "gnu") == 0)
    479 	    vendor = OBJ_ATTR_GNU;
    480 	  else
    481 	    {
    482 	      /* Other vendor section.  Ignore it.  */
    483 	      p += namelen + section_len;
    484 	      continue;
    485 	    }
    486 
    487 	  p += namelen;
    488 	  while (section_len > 0 && p < p_end)
    489 	    {
    490 	      unsigned int tag;
    491 	      unsigned int n;
    492 	      unsigned int val;
    493 	      bfd_vma subsection_len;
    494 	      bfd_byte *end;
    495 
    496 	      tag = safe_read_leb128 (abfd, p, &n, FALSE, p_end);
    497 	      p += n;
    498 	      if (p < p_end - 4)
    499 		subsection_len = bfd_get_32 (abfd, p);
    500 	      else
    501 		subsection_len = 0;
    502 	      p += 4;
    503 	      if (subsection_len == 0)
    504 		break;
    505 	      if (subsection_len > section_len)
    506 		subsection_len = section_len;
    507 	      section_len -= subsection_len;
    508 	      subsection_len -= n + 4;
    509 	      end = p + subsection_len;
    510 	      /* PR 17512: file: 0e8c0c90.  */
    511 	      if (end > p_end)
    512 		end = p_end;
    513 	      switch (tag)
    514 		{
    515 		case Tag_File:
    516 		  while (p < end)
    517 		    {
    518 		      int type;
    519 
    520 		      tag = safe_read_leb128 (abfd, p, &n, FALSE, end);
    521 		      p += n;
    522 		      type = _bfd_elf_obj_attrs_arg_type (abfd, vendor, tag);
    523 		      switch (type & (ATTR_TYPE_FLAG_INT_VAL | ATTR_TYPE_FLAG_STR_VAL))
    524 			{
    525 			case ATTR_TYPE_FLAG_INT_VAL | ATTR_TYPE_FLAG_STR_VAL:
    526 			  val = safe_read_leb128 (abfd, p, &n, FALSE, end);
    527 			  p += n;
    528 			  bfd_elf_add_obj_attr_int_string (abfd, vendor, tag,
    529 							   val, (char *) p);
    530 			  p += strlen ((char *)p) + 1;
    531 			  break;
    532 			case ATTR_TYPE_FLAG_STR_VAL:
    533 			  bfd_elf_add_obj_attr_string (abfd, vendor, tag,
    534 						       (char *) p);
    535 			  p += strlen ((char *)p) + 1;
    536 			  break;
    537 			case ATTR_TYPE_FLAG_INT_VAL:
    538 			  val = safe_read_leb128 (abfd, p, &n, FALSE, end);
    539 			  p += n;
    540 			  bfd_elf_add_obj_attr_int (abfd, vendor, tag, val);
    541 			  break;
    542 			default:
    543 			  abort ();
    544 			}
    545 		    }
    546 		  break;
    547 		case Tag_Section:
    548 		case Tag_Symbol:
    549 		  /* Don't have anywhere convenient to attach these.
    550 		     Fall through for now.  */
    551 		default:
    552 		  /* Ignore things we don't kow about.  */
    553 		  p += subsection_len;
    554 		  subsection_len = 0;
    555 		  break;
    556 		}
    557 	    }
    558 	}
    559     }
    560   free (contents);
    561 }
    562 
    563 /* Merge common object attributes from IBFD into OBFD.  Raise an error
    564    if there are conflicting attributes.  Any processor-specific
    565    attributes have already been merged.  This must be called from the
    566    bfd_elfNN_bfd_merge_private_bfd_data hook for each individual
    567    target, along with any target-specific merging.  Because there are
    568    no common attributes other than Tag_compatibility at present, and
    569    non-"gnu" Tag_compatibility is not expected in "gnu" sections, this
    570    is not presently called for targets without their own
    571    attributes.  */
    572 
    573 bfd_boolean
    574 _bfd_elf_merge_object_attributes (bfd *ibfd, bfd *obfd)
    575 {
    576   obj_attribute *in_attr;
    577   obj_attribute *out_attr;
    578   int vendor;
    579 
    580   /* The only common attribute is currently Tag_compatibility,
    581      accepted in both processor and "gnu" sections.  */
    582   for (vendor = OBJ_ATTR_FIRST; vendor <= OBJ_ATTR_LAST; vendor++)
    583     {
    584       /* Handle Tag_compatibility.  The tags are only compatible if the flags
    585 	 are identical and, if the flags are '1', the strings are identical.
    586 	 If the flags are non-zero, then we can only use the string "gnu".  */
    587       in_attr = &elf_known_obj_attributes (ibfd)[vendor][Tag_compatibility];
    588       out_attr = &elf_known_obj_attributes (obfd)[vendor][Tag_compatibility];
    589 
    590       if (in_attr->i > 0 && strcmp (in_attr->s, "gnu") != 0)
    591 	{
    592 	  _bfd_error_handler
    593 		(_("error: %B: Object has vendor-specific contents that "
    594 		   "must be processed by the '%s' toolchain"),
    595 		 ibfd, in_attr->s);
    596 	  return FALSE;
    597 	}
    598 
    599       if (in_attr->i != out_attr->i
    600 	  || (in_attr->i != 0 && strcmp (in_attr->s, out_attr->s) != 0))
    601 	{
    602 	  _bfd_error_handler (_("error: %B: Object tag '%d, %s' is "
    603 				"incompatible with tag '%d, %s'"),
    604 			      ibfd,
    605 			      in_attr->i, in_attr->s ? in_attr->s : "",
    606 			      out_attr->i, out_attr->s ? out_attr->s : "");
    607 	  return FALSE;
    608 	}
    609     }
    610 
    611   return TRUE;
    612 }
    613 
    614 /* Merge an unknown processor-specific attribute TAG, within the range
    615    of known attributes, from IBFD into OBFD; return TRUE if the link
    616    is OK, FALSE if it must fail.  */
    617 
    618 bfd_boolean
    619 _bfd_elf_merge_unknown_attribute_low (bfd *ibfd, bfd *obfd, int tag)
    620 {
    621   obj_attribute *in_attr;
    622   obj_attribute *out_attr;
    623   bfd *err_bfd = NULL;
    624   bfd_boolean result = TRUE;
    625 
    626   in_attr = elf_known_obj_attributes_proc (ibfd);
    627   out_attr = elf_known_obj_attributes_proc (obfd);
    628 
    629   if (out_attr[tag].i != 0 || out_attr[tag].s != NULL)
    630     err_bfd = obfd;
    631   else if (in_attr[tag].i != 0 || in_attr[tag].s != NULL)
    632     err_bfd = ibfd;
    633 
    634   if (err_bfd != NULL)
    635     result
    636       = get_elf_backend_data (err_bfd)->obj_attrs_handle_unknown (err_bfd, tag);
    637 
    638   /* Only pass on attributes that match in both inputs.  */
    639   if (in_attr[tag].i != out_attr[tag].i
    640       || (in_attr[tag].s == NULL) != (out_attr[tag].s == NULL)
    641       || (in_attr[tag].s != NULL && out_attr[tag].s != NULL
    642 	  && strcmp (in_attr[tag].s, out_attr[tag].s) != 0))
    643     {
    644       out_attr[tag].i = 0;
    645       out_attr[tag].s = NULL;
    646     }
    647 
    648   return result;
    649 }
    650 
    651 /* Merge the lists of unknown processor-specific attributes, outside
    652    the known range, from IBFD into OBFD; return TRUE if the link is
    653    OK, FALSE if it must fail.  */
    654 
    655 bfd_boolean
    656 _bfd_elf_merge_unknown_attribute_list (bfd *ibfd, bfd *obfd)
    657 {
    658   obj_attribute_list *in_list;
    659   obj_attribute_list *out_list;
    660   obj_attribute_list **out_listp;
    661   bfd_boolean result = TRUE;
    662 
    663   in_list = elf_other_obj_attributes_proc (ibfd);
    664   out_listp = &elf_other_obj_attributes_proc (obfd);
    665   out_list = *out_listp;
    666 
    667   for (; in_list || out_list; )
    668     {
    669       bfd *err_bfd = NULL;
    670       unsigned int err_tag = 0;
    671 
    672       /* The tags for each list are in numerical order.  */
    673       /* If the tags are equal, then merge.  */
    674       if (out_list && (!in_list || in_list->tag > out_list->tag))
    675 	{
    676 	  /* This attribute only exists in obfd.  We can't merge, and we don't
    677 	     know what the tag means, so delete it.  */
    678 	  err_bfd = obfd;
    679 	  err_tag = out_list->tag;
    680 	  *out_listp = out_list->next;
    681 	  out_list = *out_listp;
    682 	}
    683       else if (in_list && (!out_list || in_list->tag < out_list->tag))
    684 	{
    685 	  /* This attribute only exists in ibfd. We can't merge, and we don't
    686 	     know what the tag means, so ignore it.  */
    687 	  err_bfd = ibfd;
    688 	  err_tag = in_list->tag;
    689 	  in_list = in_list->next;
    690 	}
    691       else /* The tags are equal.  */
    692 	{
    693 	  /* As present, all attributes in the list are unknown, and
    694 	     therefore can't be merged meaningfully.  */
    695 	  err_bfd = obfd;
    696 	  err_tag = out_list->tag;
    697 
    698 	  /*  Only pass on attributes that match in both inputs.  */
    699 	  if (in_list->attr.i != out_list->attr.i
    700 	      || (in_list->attr.s == NULL) != (out_list->attr.s == NULL)
    701 	      || (in_list->attr.s && out_list->attr.s
    702 		  && strcmp (in_list->attr.s, out_list->attr.s) != 0))
    703 	    {
    704 	      /* No match.  Delete the attribute.  */
    705 	      *out_listp = out_list->next;
    706 	      out_list = *out_listp;
    707 	    }
    708 	  else
    709 	    {
    710 	      /* Matched.  Keep the attribute and move to the next.  */
    711 	      out_list = out_list->next;
    712 	      in_list = in_list->next;
    713 	    }
    714 	}
    715 
    716       if (err_bfd)
    717 	result = result
    718 	  && get_elf_backend_data (err_bfd)->obj_attrs_handle_unknown (err_bfd,
    719 								       err_tag);
    720     }
    721 
    722   return result;
    723 }
    724