bfd/elf-attrs.c

   1 /* ELF attributes support (based on ARM EABI attributes).
   2    Copyright (C) 2005-2015 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);
 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);
 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);
 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 }