bfd/elf-attrs.c

   1 /* ELF attributes support (based on ARM EABI attributes).
   2    Copyright 2005, 2006, 2007, 2009, 2010
   3    Free Software Foundation, Inc.
   4
   5    This file is part of BFD, the Binary File Descriptor library.
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 3 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program; if not, write to the Free Software
  19    Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
  20    MA 02110-1301, USA.  */
  21
  22 #include "sysdep.h"
  23 #include "bfd.h"
  24 #include "libiberty.h"
  25 #include "libbfd.h"
  26 #include "elf-bfd.h"
  27
  28 /* Return the number of bytes needed by I in uleb128 format.  */
  29 static int
  30 uleb128_size (unsigned int i)
  31 {
  32   int size;
  33   size = 1;
  34   while (i >= 0x80)
  35     {
  36       i >>= 7;
  37       size++;
  38     }
  39   return size;
  40 }
  41
  42 /* Return TRUE if the attribute has the default value (0/"").  */
  43 static bfd_boolean
  44 is_default_attr (obj_attribute *attr)
  45 {
  46   if (ATTR_TYPE_HAS_INT_VAL (attr->type) && attr->i != 0)
  47     return FALSE;
  48   if (ATTR_TYPE_HAS_STR_VAL (attr->type) && attr->s && *attr->s)
  49     return FALSE;
  50   if (ATTR_TYPE_HAS_NO_DEFAULT (attr->type))
  51     return FALSE;
  52
  53   return TRUE;
  54 }
  55
  56 /* Return the size of a single attribute.  */
  57 static bfd_vma
  58 obj_attr_size (int tag, obj_attribute *attr)
  59 {
  60   bfd_vma size;
  61
  62   if (is_default_attr (attr))
  63     return 0;
  64
  65   size = uleb128_size (tag);
  66   if (ATTR_TYPE_HAS_INT_VAL (attr->type))
  67     size += uleb128_size (attr->i);
  68   if (ATTR_TYPE_HAS_STR_VAL (attr->type))
  69     size += strlen ((char *)attr->s) + 1;
  70   return size;
  71 }
  72
  73 /* Return the vendor name for a given object attributes section.  */
  74 static const char *
  75 vendor_obj_attr_name (bfd *abfd, int vendor)
  76 {
  77   return (vendor == OBJ_ATTR_PROC
  78           ? get_elf_backend_data (abfd)->obj_attrs_vendor
  79           : "gnu");
  80 }
  81
  82 /* Return the size of the object attributes section for VENDOR
  83    (OBJ_ATTR_PROC or OBJ_ATTR_GNU), or 0 if there are no attributes
  84    for that vendor to record and the vendor is OBJ_ATTR_GNU.  */
  85 static bfd_vma
  86 vendor_obj_attr_size (bfd *abfd, int vendor)
  87 {
  88   bfd_vma size;
  89   obj_attribute *attr;
  90   obj_attribute_list *list;
  91   int i;
  92   const char *vendor_name = vendor_obj_attr_name (abfd, vendor);
  93
  94   if (!vendor_name)
  95     return 0;
  96
  97   attr = elf_known_obj_attributes (abfd)[vendor];
  98   size = 0;
  99   for (i = LEAST_KNOWN_OBJ_ATTRIBUTE; i < NUM_KNOWN_OBJ_ATTRIBUTES; i++)
 100     size += obj_attr_size (i, &attr[i]);
 101
 102   for (list = elf_other_obj_attributes (abfd)[vendor];
 103        list;
 104        list = list->next)
 105     size += obj_attr_size (list->tag, &list->attr);
 106
 107   /* <size> <vendor_name> NUL 0x1 <size> */
 108   return ((size || vendor == OBJ_ATTR_PROC)
 109           ? size + 10 + strlen (vendor_name)
 110           : 0);
 111 }
 112
 113 /* Return the size of the object attributes section.  */
 114 bfd_vma
 115 bfd_elf_obj_attr_size (bfd *abfd)
 116 {
 117   bfd_vma size;
 118
 119   size = vendor_obj_attr_size (abfd, OBJ_ATTR_PROC);
 120   size += vendor_obj_attr_size (abfd, OBJ_ATTR_GNU);
 121
 122   /* 'A' <sections for each vendor> */
 123   return (size ? size + 1 : 0);
 124 }
 125
 126 /* Write VAL in uleb128 format to P, returning a pointer to the
 127    following byte.  */
 128 static bfd_byte *
 129 write_uleb128 (bfd_byte *p, unsigned int val)
 130 {
 131   bfd_byte c;
 132   do
 133     {
 134       c = val & 0x7f;
 135       val >>= 7;
 136       if (val)
 137         c |= 0x80;
 138       *(p++) = c;
 139     }
 140   while (val);
 141   return p;
 142 }
 143
 144 /* Write attribute ATTR to butter P, and return a pointer to the following
 145    byte.  */
 146 static bfd_byte *
 147 write_obj_attribute (bfd_byte *p, int tag, obj_attribute *attr)
 148 {
 149   /* Suppress default entries.  */
 150   if (is_default_attr (attr))
 151     return p;
 152
 153   p = write_uleb128 (p, tag);
 154   if (ATTR_TYPE_HAS_INT_VAL (attr->type))
 155     p = write_uleb128 (p, attr->i);
 156   if (ATTR_TYPE_HAS_STR_VAL (attr->type))
 157     {
 158       int len;
 159
 160       len = strlen (attr->s) + 1;
 161       memcpy (p, attr->s, len);
 162       p += len;
 163     }
 164
 165   return p;
 166 }
 167
 168 /* Write the contents of the object attributes section (length SIZE)
 169    for VENDOR to CONTENTS.  */
 170 static void
 171 vendor_set_obj_attr_contents (bfd *abfd, bfd_byte *contents, bfd_vma size,
 172                               int vendor)
 173 {
 174   bfd_byte *p;
 175   obj_attribute *attr;
 176   obj_attribute_list *list;
 177   int i;
 178   const char *vendor_name = vendor_obj_attr_name (abfd, vendor);
 179   size_t vendor_length = strlen (vendor_name) + 1;
 180
 181   p = contents;
 182   bfd_put_32 (abfd, size, p);
 183   p += 4;
 184   memcpy (p, vendor_name, vendor_length);
 185   p += vendor_length;
 186   *(p++) = Tag_File;
 187   bfd_put_32 (abfd, size - 4 - vendor_length, p);
 188   p += 4;
 189
 190   attr = elf_known_obj_attributes (abfd)[vendor];
 191   for (i = LEAST_KNOWN_OBJ_ATTRIBUTE; i < NUM_KNOWN_OBJ_ATTRIBUTES; i++)
 192     {
 193       int tag = i;
 194       if (get_elf_backend_data (abfd)->obj_attrs_order)
 195         tag = get_elf_backend_data (abfd)->obj_attrs_order (i);
 196       p = write_obj_attribute (p, tag, &attr[tag]);
 197     }
 198
 199   for (list = elf_other_obj_attributes (abfd)[vendor];
 200        list;
 201        list = list->next)
 202     p = write_obj_attribute (p, list->tag, &list->attr);
 203 }
 204
 205 /* Write the contents of the object attributes section to CONTENTS.  */
 206 void
 207 bfd_elf_set_obj_attr_contents (bfd *abfd, bfd_byte *contents, bfd_vma size)
 208 {
 209   bfd_byte *p;
 210   int vendor;
 211   bfd_vma my_size;
 212
 213   p = contents;
 214   *(p++) = 'A';
 215   my_size = 1;
 216   for (vendor = OBJ_ATTR_FIRST; vendor <= OBJ_ATTR_LAST; vendor++)
 217     {
 218       bfd_vma vendor_size = vendor_obj_attr_size (abfd, vendor);
 219       if (vendor_size)
 220         vendor_set_obj_attr_contents (abfd, p, vendor_size, vendor);
 221       p += vendor_size;
 222       my_size += vendor_size;
 223     }
 224
 225   if (size != my_size)
 226     abort ();
 227 }
 228
 229 /* Allocate/find an object attribute.  */
 230 static obj_attribute *
 231 elf_new_obj_attr (bfd *abfd, int vendor, int tag)
 232 {
 233   obj_attribute *attr;
 234   obj_attribute_list *list;
 235   obj_attribute_list *p;
 236   obj_attribute_list **lastp;
 237
 238
 239   if (tag < NUM_KNOWN_OBJ_ATTRIBUTES)
 240     {
 241       /* Known tags are preallocated.  */
 242       attr = &elf_known_obj_attributes (abfd)[vendor][tag];
 243     }
 244   else
 245     {
 246       /* Create a new tag.  */
 247       list = (obj_attribute_list *)
 248         bfd_alloc (abfd, sizeof (obj_attribute_list));
 249       memset (list, 0, sizeof (obj_attribute_list));
 250       list->tag = tag;
 251       /* Keep the tag list in order.  */
 252       lastp = &elf_other_obj_attributes (abfd)[vendor];
 253       for (p = *lastp; p; p = p->next)
 254         {
 255           if (tag < p->tag)
 256             break;
 257           lastp = &p->next;
 258         }
 259       list->next = *lastp;
 260       *lastp = list;
 261       attr = &list->attr;
 262     }
 263
 264   return attr;
 265 }
 266
 267 /* Return the value of an integer object attribute.  */
 268 int
 269 bfd_elf_get_obj_attr_int (bfd *abfd, int vendor, int tag)
 270 {
 271   obj_attribute_list *p;
 272
 273   if (tag < NUM_KNOWN_OBJ_ATTRIBUTES)
 274     {
 275       /* Known tags are preallocated.  */
 276       return elf_known_obj_attributes (abfd)[vendor][tag].i;
 277     }
 278   else
 279     {
 280       for (p = elf_other_obj_attributes (abfd)[vendor];
 281            p;
 282            p = p->next)
 283         {
 284           if (tag == p->tag)
 285             return p->attr.i;
 286           if (tag < p->tag)
 287             break;
 288         }
 289       return 0;
 290     }
 291 }
 292
 293 /* Add an integer object attribute.  */
 294 void
 295 bfd_elf_add_obj_attr_int (bfd *abfd, int vendor, int tag, unsigned int i)
 296 {
 297   obj_attribute *attr;
 298
 299   attr = elf_new_obj_attr (abfd, vendor, tag);
 300   attr->type = _bfd_elf_obj_attrs_arg_type (abfd, vendor, tag);
 301   attr->i = i;
 302 }
 303
 304 /* Duplicate an object attribute string value.  */
 305 char *
 306 _bfd_elf_attr_strdup (bfd *abfd, const char * s)
 307 {
 308   char * p;
 309   int len;
 310
 311   len = strlen (s) + 1;
 312   p = (char *) bfd_alloc (abfd, len);
 313   return (char *) memcpy (p, s, len);
 314 }
 315
 316 /* Add a string object attribute.  */
 317 void
 318 bfd_elf_add_obj_attr_string (bfd *abfd, int vendor, int tag, const char *s)
 319 {
 320   obj_attribute *attr;
 321
 322   attr = elf_new_obj_attr (abfd, vendor, tag);
 323   attr->type = _bfd_elf_obj_attrs_arg_type (abfd, vendor, tag);
 324   attr->s = _bfd_elf_attr_strdup (abfd, s);
 325 }
 326
 327 /* Add a int+string object attribute.  */
 328 void
 329 bfd_elf_add_obj_attr_int_string (bfd *abfd, int vendor, 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);
 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   for (vendor = OBJ_ATTR_FIRST; vendor <= OBJ_ATTR_LAST; vendor++)
 351     {
 352       in_attr
 353         = &elf_known_obj_attributes (ibfd)[vendor][LEAST_KNOWN_OBJ_ATTRIBUTE];
 354       out_attr
 355         = &elf_known_obj_attributes (obfd)[vendor][LEAST_KNOWN_OBJ_ATTRIBUTE];
 356       for (i = LEAST_KNOWN_OBJ_ATTRIBUTE; i < NUM_KNOWN_OBJ_ATTRIBUTES; i++)
 357         {
 358           out_attr->type = in_attr->type;
 359           out_attr->i = in_attr->i;
 360           if (in_attr->s && *in_attr->s)
 361             out_attr->s = _bfd_elf_attr_strdup (obfd, in_attr->s);
 362           in_attr++;
 363           out_attr++;
 364         }
 365
 366       for (list = elf_other_obj_attributes (ibfd)[vendor];
 367            list;
 368            list = list->next)
 369         {
 370           in_attr = &list->attr;
 371           switch (in_attr->type & (ATTR_TYPE_FLAG_INT_VAL | ATTR_TYPE_FLAG_STR_VAL))
 372             {
 373             case ATTR_TYPE_FLAG_INT_VAL:
 374               bfd_elf_add_obj_attr_int (obfd, vendor, list->tag, in_attr->i);
 375               break;
 376             case ATTR_TYPE_FLAG_STR_VAL:
 377               bfd_elf_add_obj_attr_string (obfd, vendor, list->tag,
 378                                            in_attr->s);
 379               break;
 380             case ATTR_TYPE_FLAG_INT_VAL | ATTR_TYPE_FLAG_STR_VAL:
 381               bfd_elf_add_obj_attr_int_string (obfd, vendor, list->tag,
 382                                                in_attr->i, in_attr->s);
 383               break;
 384             default:
 385               abort ();
 386             }
 387         }
 388     }
 389 }
 390
 391 /* Determine whether a GNU object attribute tag takes an integer, a
 392    string or both.  */
 393 static int
 394 gnu_obj_attrs_arg_type (int tag)
 395 {
 396   /* Except for Tag_compatibility, for GNU attributes we follow the
 397      same rule ARM ones > 32 follow: odd-numbered tags take strings
 398      and even-numbered tags take integers.  In addition, tag & 2 is
 399      nonzero for architecture-independent tags and zero for
 400      architecture-dependent ones.  */
 401   if (tag == Tag_compatibility)
 402     return 3;
 403   else
 404     return (tag & 1) != 0 ? 2 : 1;
 405 }
 406
 407 /* Determine what arguments an attribute tag takes.  */
 408 int
 409 _bfd_elf_obj_attrs_arg_type (bfd *abfd, int vendor, int tag)
 410 {
 411   switch (vendor)
 412     {
 413     case OBJ_ATTR_PROC:
 414       return get_elf_backend_data (abfd)->obj_attrs_arg_type (tag);
 415       break;
 416     case OBJ_ATTR_GNU:
 417       return gnu_obj_attrs_arg_type (tag);
 418       break;
 419     default:
 420       abort ();
 421     }
 422 }
 423
 424 /* Parse an object attributes section.  */
 425 void
 426 _bfd_elf_parse_attributes (bfd *abfd, Elf_Internal_Shdr * hdr)
 427 {
 428   bfd_byte *contents;
 429   bfd_byte *p;
 430   bfd_vma len;
 431   const char *std_section;
 432
 433   contents = (bfd_byte *) bfd_malloc (hdr->sh_size);
 434   if (!contents)
 435     return;
 436   if (!bfd_get_section_contents (abfd, hdr->bfd_section, contents, 0,
 437                                  hdr->sh_size))
 438     {
 439       free (contents);
 440       return;
 441     }
 442   p = contents;
 443   std_section = get_elf_backend_data (abfd)->obj_attrs_vendor;
 444   if (*(p++) == 'A')
 445     {
 446       len = hdr->sh_size - 1;
 447       while (len > 0)
 448         {
 449           int namelen;
 450           bfd_vma section_len;
 451           int vendor;
 452
 453           section_len = bfd_get_32 (abfd, p);
 454           p += 4;
 455           if (section_len > len)
 456             section_len = len;
 457           len -= section_len;
 458           namelen = strlen ((char *)p) + 1;
 459           section_len -= namelen + 4;
 460           if (std_section && strcmp ((char *)p, std_section) == 0)
 461             vendor = OBJ_ATTR_PROC;
 462           else if (strcmp ((char *)p, "gnu") == 0)
 463             vendor = OBJ_ATTR_GNU;
 464           else
 465             {
 466               /* Other vendor section.  Ignore it.  */
 467               p += namelen + section_len;
 468               continue;
 469             }
 470
 471           p += namelen;
 472           while (section_len > 0)
 473             {
 474               int tag;
 475               unsigned int n;
 476               unsigned int val;
 477               bfd_vma subsection_len;
 478               bfd_byte *end;
 479
 480               tag = read_unsigned_leb128 (abfd, p, &n);
 481               p += n;
 482               subsection_len = bfd_get_32 (abfd, p);
 483               p += 4;
 484               if (subsection_len > section_len)
 485                 subsection_len = section_len;
 486               section_len -= subsection_len;
 487               subsection_len -= n + 4;
 488               end = p + subsection_len;
 489               switch (tag)
 490                 {
 491                 case Tag_File:
 492                   while (p < end)
 493                     {
 494                       int type;
 495
 496                       tag = read_unsigned_leb128 (abfd, p, &n);
 497                       p += n;
 498                       type = _bfd_elf_obj_attrs_arg_type (abfd, vendor, tag);
 499                       switch (type & (ATTR_TYPE_FLAG_INT_VAL | ATTR_TYPE_FLAG_STR_VAL))
 500                         {
 501                         case ATTR_TYPE_FLAG_INT_VAL | ATTR_TYPE_FLAG_STR_VAL:
 502                           val = read_unsigned_leb128 (abfd, p, &n);
 503                           p += n;
 504                           bfd_elf_add_obj_attr_int_string (abfd, vendor, tag,
 505                                                            val, (char *)p);
 506                           p += strlen ((char *)p) + 1;
 507                           break;
 508                         case ATTR_TYPE_FLAG_STR_VAL:
 509                           bfd_elf_add_obj_attr_string (abfd, vendor, tag,
 510                                                        (char *)p);
 511                           p += strlen ((char *)p) + 1;
 512                           break;
 513                         case ATTR_TYPE_FLAG_INT_VAL:
 514                           val = read_unsigned_leb128 (abfd, p, &n);
 515                           p += n;
 516                           bfd_elf_add_obj_attr_int (abfd, vendor, tag, val);
 517                           break;
 518                         default:
 519                           abort ();
 520                         }
 521                     }
 522                   break;
 523                 case Tag_Section:
 524                 case Tag_Symbol:
 525                   /* Don't have anywhere convenient to attach these.
 526                      Fall through for now.  */
 527                 default:
 528                   /* Ignore things we don't kow about.  */
 529                   p += subsection_len;
 530                   subsection_len = 0;
 531                   break;
 532                 }
 533             }
 534         }
 535     }
 536   free (contents);
 537 }
 538
 539 /* Merge common object attributes from IBFD into OBFD.  Raise an error
 540    if there are conflicting attributes.  Any processor-specific
 541    attributes have already been merged.  This must be called from the
 542    bfd_elfNN_bfd_merge_private_bfd_data hook for each individual
 543    target, along with any target-specific merging.  Because there are
 544    no common attributes other than Tag_compatibility at present, and
 545    non-"gnu" Tag_compatibility is not expected in "gnu" sections, this
 546    is not presently called for targets without their own
 547    attributes.  */
 548
 549 bfd_boolean
 550 _bfd_elf_merge_object_attributes (bfd *ibfd, bfd *obfd)
 551 {
 552   obj_attribute *in_attr;
 553   obj_attribute *out_attr;
 554   int vendor;
 555
 556   /* The only common attribute is currently Tag_compatibility,
 557      accepted in both processor and "gnu" sections.  */
 558   for (vendor = OBJ_ATTR_FIRST; vendor <= OBJ_ATTR_LAST; vendor++)
 559     {
 560       /* Handle Tag_compatibility.  The tags are only compatible if the flags
 561          are identical and, if the flags are '1', the strings are identical.
 562          If the flags are non-zero, then we can only use the string "gnu".  */
 563       in_attr = &elf_known_obj_attributes (ibfd)[vendor][Tag_compatibility];
 564       out_attr = &elf_known_obj_attributes (obfd)[vendor][Tag_compatibility];
 565
 566       if (in_attr->i > 0 && strcmp (in_attr->s, "gnu") != 0)
 567         {
 568           _bfd_error_handler
 569                 (_("error: %B: Object has vendor-specific contents that "
 570                    "must be processed by the '%s' toolchain"),
 571                  ibfd, in_attr->s);
 572           return FALSE;
 573         }
 574
 575       if (in_attr->i != out_attr->i
 576           || (in_attr->i != 0 && strcmp (in_attr->s, out_attr->s) != 0))
 577         {
 578           _bfd_error_handler (_("error: %B: Object tag '%d, %s' is "
 579                                 "incompatible with tag '%d, %s'"),
 580                               ibfd,
 581                               in_attr->i, in_attr->s ? in_attr->s : "",
 582                               out_attr->i, out_attr->s ? out_attr->s : "");
 583           return FALSE;
 584         }
 585     }
 586
 587   return TRUE;
 588 }
 589
 590 /* Merge an unknown processor-specific attribute TAG, within the range
 591    of known attributes, from IBFD into OBFD; return TRUE if the link
 592    is OK, FALSE if it must fail.  */
 593
 594 bfd_boolean
 595 _bfd_elf_merge_unknown_attribute_low (bfd *ibfd, bfd *obfd, int tag)
 596 {
 597   obj_attribute *in_attr;
 598   obj_attribute *out_attr;
 599   bfd *err_bfd = NULL;
 600   bfd_boolean result = TRUE;
 601
 602   in_attr = elf_known_obj_attributes_proc (ibfd);
 603   out_attr = elf_known_obj_attributes_proc (obfd);
 604
 605   if (out_attr[tag].i != 0 || out_attr[tag].s != NULL)
 606     err_bfd = obfd;
 607   else if (in_attr[tag].i != 0 || in_attr[tag].s != NULL)
 608     err_bfd = ibfd;
 609
 610   if (err_bfd != NULL)
 611     result
 612       = get_elf_backend_data (err_bfd)->obj_attrs_handle_unknown (err_bfd, tag);
 613
 614   /* Only pass on attributes that match in both inputs.  */
 615   if (in_attr[tag].i != out_attr[tag].i
 616       || (in_attr[tag].s == NULL) != (out_attr[tag].s == NULL)
 617       || (in_attr[tag].s != NULL && out_attr[tag].s != NULL
 618           && strcmp (in_attr[tag].s, out_attr[tag].s) != 0))
 619     {
 620       out_attr[tag].i = 0;
 621       out_attr[tag].s = NULL;
 622     }
 623
 624   return result;
 625 }
 626
 627 /* Merge the lists of unknown processor-specific attributes, outside
 628    the known range, from IBFD into OBFD; return TRUE if the link is
 629    OK, FALSE if it must fail.  */
 630
 631 bfd_boolean
 632 _bfd_elf_merge_unknown_attribute_list (bfd *ibfd, bfd *obfd)
 633 {
 634   obj_attribute_list *in_list;
 635   obj_attribute_list *out_list;
 636   obj_attribute_list **out_listp;
 637   bfd_boolean result = TRUE;
 638
 639   in_list = elf_other_obj_attributes_proc (ibfd);
 640   out_listp = &elf_other_obj_attributes_proc (obfd);
 641   out_list = *out_listp;
 642
 643   for (; in_list || out_list; )
 644     {
 645       bfd *err_bfd = NULL;
 646       int err_tag = 0;
 647
 648       /* The tags for each list are in numerical order.  */
 649       /* If the tags are equal, then merge.  */
 650       if (out_list && (!in_list || in_list->tag > out_list->tag))
 651         {
 652           /* This attribute only exists in obfd.  We can't merge, and we don't
 653              know what the tag means, so delete it.  */
 654           err_bfd = obfd;
 655           err_tag = out_list->tag;
 656           *out_listp = out_list->next;
 657           out_list = *out_listp;
 658         }
 659       else if (in_list && (!out_list || in_list->tag < out_list->tag))
 660         {
 661           /* This attribute only exists in ibfd. We can't merge, and we don't
 662              know what the tag means, so ignore it.  */
 663           err_bfd = ibfd;
 664           err_tag = in_list->tag;
 665           in_list = in_list->next;
 666         }
 667       else /* The tags are equal.  */
 668         {
 669           /* As present, all attributes in the list are unknown, and
 670              therefore can't be merged meaningfully.  */
 671           err_bfd = obfd;
 672           err_tag = out_list->tag;
 673
 674           /*  Only pass on attributes that match in both inputs.  */
 675           if (in_list->attr.i != out_list->attr.i
 676               || (in_list->attr.s == NULL) != (out_list->attr.s == NULL)
 677               || (in_list->attr.s && out_list->attr.s
 678                   && strcmp (in_list->attr.s, out_list->attr.s) != 0))
 679             {
 680               /* No match.  Delete the attribute.  */
 681               *out_listp = out_list->next;
 682               out_list = *out_listp;
 683             }
 684           else
 685             {
 686               /* Matched.  Keep the attribute and move to the next.  */
 687               out_list = out_list->next;
 688               in_list = in_list->next;
 689             }
 690         }
 691
 692       if (err_bfd)
 693         result = result
 694           && get_elf_backend_data (err_bfd)->obj_attrs_handle_unknown (err_bfd,
 695                                                                        err_tag);
 696     }
 697
 698   return result;
 699 }