| 1 | /* ELF STT_GNU_IFUNC support. |
| 2 | Copyright (C) 2009-2016 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 "bfdlink.h" |
| 24 | #include "libbfd.h" |
| 25 | #define ARCH_SIZE 0 |
| 26 | #include "elf-bfd.h" |
| 27 | #include "safe-ctype.h" |
| 28 | #include "libiberty.h" |
| 29 | #include "objalloc.h" |
| 30 | |
| 31 | /* Create sections needed by STT_GNU_IFUNC symbol. */ |
| 32 | |
| 33 | bfd_boolean |
| 34 | _bfd_elf_create_ifunc_sections (bfd *abfd, struct bfd_link_info *info) |
| 35 | { |
| 36 | flagword flags, pltflags; |
| 37 | asection *s; |
| 38 | const struct elf_backend_data *bed = get_elf_backend_data (abfd); |
| 39 | struct elf_link_hash_table *htab = elf_hash_table (info); |
| 40 | |
| 41 | if (htab->irelifunc != NULL || htab->iplt != NULL) |
| 42 | return TRUE; |
| 43 | |
| 44 | flags = bed->dynamic_sec_flags; |
| 45 | pltflags = flags; |
| 46 | if (bed->plt_not_loaded) |
| 47 | /* We do not clear SEC_ALLOC here because we still want the OS to |
| 48 | allocate space for the section; it's just that there's nothing |
| 49 | to read in from the object file. */ |
| 50 | pltflags &= ~ (SEC_CODE | SEC_LOAD | SEC_HAS_CONTENTS); |
| 51 | else |
| 52 | pltflags |= SEC_ALLOC | SEC_CODE | SEC_LOAD; |
| 53 | if (bed->plt_readonly) |
| 54 | pltflags |= SEC_READONLY; |
| 55 | |
| 56 | if (bfd_link_pic (info)) |
| 57 | { |
| 58 | /* We need to create .rel[a].ifunc for PIC objects. */ |
| 59 | const char *rel_sec = (bed->rela_plts_and_copies_p |
| 60 | ? ".rela.ifunc" : ".rel.ifunc"); |
| 61 | |
| 62 | s = bfd_make_section_with_flags (abfd, rel_sec, |
| 63 | flags | SEC_READONLY); |
| 64 | if (s == NULL |
| 65 | || ! bfd_set_section_alignment (abfd, s, |
| 66 | bed->s->log_file_align)) |
| 67 | return FALSE; |
| 68 | htab->irelifunc = s; |
| 69 | } |
| 70 | else |
| 71 | { |
| 72 | /* We need to create .iplt, .rel[a].iplt, .igot and .igot.plt |
| 73 | for static executables. */ |
| 74 | s = bfd_make_section_with_flags (abfd, ".iplt", pltflags); |
| 75 | if (s == NULL |
| 76 | || ! bfd_set_section_alignment (abfd, s, bed->plt_alignment)) |
| 77 | return FALSE; |
| 78 | htab->iplt = s; |
| 79 | |
| 80 | s = bfd_make_section_with_flags (abfd, |
| 81 | (bed->rela_plts_and_copies_p |
| 82 | ? ".rela.iplt" : ".rel.iplt"), |
| 83 | flags | SEC_READONLY); |
| 84 | if (s == NULL |
| 85 | || ! bfd_set_section_alignment (abfd, s, |
| 86 | bed->s->log_file_align)) |
| 87 | return FALSE; |
| 88 | htab->irelplt = s; |
| 89 | |
| 90 | /* We don't need the .igot section if we have the .igot.plt |
| 91 | section. */ |
| 92 | if (bed->want_got_plt) |
| 93 | s = bfd_make_section_with_flags (abfd, ".igot.plt", flags); |
| 94 | else |
| 95 | s = bfd_make_section_with_flags (abfd, ".igot", flags); |
| 96 | if (s == NULL |
| 97 | || !bfd_set_section_alignment (abfd, s, |
| 98 | bed->s->log_file_align)) |
| 99 | return FALSE; |
| 100 | htab->igotplt = s; |
| 101 | } |
| 102 | |
| 103 | return TRUE; |
| 104 | } |
| 105 | |
| 106 | /* Allocate space in .plt, .got and associated reloc sections for |
| 107 | dynamic relocs against a STT_GNU_IFUNC symbol definition. */ |
| 108 | |
| 109 | bfd_boolean |
| 110 | _bfd_elf_allocate_ifunc_dyn_relocs (struct bfd_link_info *info, |
| 111 | struct elf_link_hash_entry *h, |
| 112 | struct elf_dyn_relocs **head, |
| 113 | bfd_boolean *readonly_dynrelocs_against_ifunc_p, |
| 114 | unsigned int plt_entry_size, |
| 115 | unsigned int plt_header_size, |
| 116 | unsigned int got_entry_size, |
| 117 | bfd_boolean avoid_plt) |
| 118 | { |
| 119 | asection *plt, *gotplt, *relplt; |
| 120 | struct elf_dyn_relocs *p; |
| 121 | unsigned int sizeof_reloc; |
| 122 | const struct elf_backend_data *bed; |
| 123 | struct elf_link_hash_table *htab; |
| 124 | bfd_boolean readonly_dynrelocs_against_ifunc; |
| 125 | /* If AVOID_PLT is TRUE, don't use PLT if possible. */ |
| 126 | bfd_boolean use_plt = !avoid_plt || h->plt.refcount > 0; |
| 127 | bfd_boolean need_dynreloc = !use_plt || bfd_link_pic (info); |
| 128 | |
| 129 | /* When a PIC object references a STT_GNU_IFUNC symbol defined |
| 130 | in executable or it isn't referenced via PLT, the address of |
| 131 | the resolved function may be used. But in non-PIC executable, |
| 132 | the address of its .plt slot may be used. Pointer equality may |
| 133 | not work correctly. PIE or non-PLT reference should be used if |
| 134 | pointer equality is required here. */ |
| 135 | if (!need_dynreloc |
| 136 | && (h->dynindx != -1 |
| 137 | || info->export_dynamic) |
| 138 | && h->pointer_equality_needed) |
| 139 | { |
| 140 | info->callbacks->einfo |
| 141 | (_("%F%P: dynamic STT_GNU_IFUNC symbol `%s' with pointer " |
| 142 | "equality in `%B' can not be used when making an " |
| 143 | "executable; recompile with -fPIE and relink with -pie\n"), |
| 144 | h->root.root.string, |
| 145 | h->root.u.def.section->owner); |
| 146 | bfd_set_error (bfd_error_bad_value); |
| 147 | return FALSE; |
| 148 | } |
| 149 | |
| 150 | htab = elf_hash_table (info); |
| 151 | |
| 152 | /* When the symbol is marked with regular reference, if PLT isn't used |
| 153 | or we are building a PIC object, we must keep dynamic relocation |
| 154 | if there is non-GOT reference and use PLT if there is PC-relative |
| 155 | reference. */ |
| 156 | if (need_dynreloc && h->ref_regular) |
| 157 | { |
| 158 | bfd_boolean keep = FALSE; |
| 159 | for (p = *head; p != NULL; p = p->next) |
| 160 | if (p->count) |
| 161 | { |
| 162 | h->non_got_ref = 1; |
| 163 | /* Need dynamic relocations for non-GOT reference. */ |
| 164 | keep = TRUE; |
| 165 | if (p->pc_count) |
| 166 | { |
| 167 | /* Must use PLT for PC-relative reference. */ |
| 168 | use_plt = TRUE; |
| 169 | need_dynreloc = bfd_link_pic (info); |
| 170 | break; |
| 171 | } |
| 172 | } |
| 173 | if (keep) |
| 174 | goto keep; |
| 175 | } |
| 176 | |
| 177 | /* Support garbage collection against STT_GNU_IFUNC symbols. */ |
| 178 | if (h->plt.refcount <= 0 && h->got.refcount <= 0) |
| 179 | { |
| 180 | h->got = htab->init_got_offset; |
| 181 | h->plt = htab->init_plt_offset; |
| 182 | *head = NULL; |
| 183 | return TRUE; |
| 184 | } |
| 185 | |
| 186 | /* Return and discard space for dynamic relocations against it if |
| 187 | it is never referenced. */ |
| 188 | if (!h->ref_regular) |
| 189 | { |
| 190 | if (h->plt.refcount > 0 |
| 191 | || h->got.refcount > 0) |
| 192 | abort (); |
| 193 | h->got = htab->init_got_offset; |
| 194 | h->plt = htab->init_plt_offset; |
| 195 | *head = NULL; |
| 196 | return TRUE; |
| 197 | } |
| 198 | |
| 199 | keep: |
| 200 | bed = get_elf_backend_data (info->output_bfd); |
| 201 | if (bed->rela_plts_and_copies_p) |
| 202 | sizeof_reloc = bed->s->sizeof_rela; |
| 203 | else |
| 204 | sizeof_reloc = bed->s->sizeof_rel; |
| 205 | |
| 206 | /* When building a static executable, use .iplt, .igot.plt and |
| 207 | .rel[a].iplt sections for STT_GNU_IFUNC symbols. */ |
| 208 | if (htab->splt != NULL) |
| 209 | { |
| 210 | plt = htab->splt; |
| 211 | gotplt = htab->sgotplt; |
| 212 | relplt = htab->srelplt; |
| 213 | |
| 214 | /* If this is the first .plt entry and PLT is used, make room for |
| 215 | the special first entry. */ |
| 216 | if (plt->size == 0 && use_plt) |
| 217 | plt->size += plt_header_size; |
| 218 | } |
| 219 | else |
| 220 | { |
| 221 | plt = htab->iplt; |
| 222 | gotplt = htab->igotplt; |
| 223 | relplt = htab->irelplt; |
| 224 | } |
| 225 | |
| 226 | if (use_plt) |
| 227 | { |
| 228 | /* Don't update value of STT_GNU_IFUNC symbol to PLT. We need |
| 229 | the original value for R_*_IRELATIVE. */ |
| 230 | h->plt.offset = plt->size; |
| 231 | |
| 232 | /* Make room for this entry in the .plt/.iplt section. */ |
| 233 | plt->size += plt_entry_size; |
| 234 | |
| 235 | /* We also need to make an entry in the .got.plt/.got.iplt section, |
| 236 | which will be placed in the .got section by the linker script. */ |
| 237 | gotplt->size += got_entry_size; |
| 238 | } |
| 239 | |
| 240 | /* We also need to make an entry in the .rel[a].plt/.rel[a].iplt |
| 241 | section for GOTPLT relocation if PLT is used. */ |
| 242 | if (use_plt) |
| 243 | { |
| 244 | relplt->size += sizeof_reloc; |
| 245 | relplt->reloc_count++; |
| 246 | } |
| 247 | |
| 248 | /* We need dynamic relocation for STT_GNU_IFUNC symbol only when |
| 249 | there is a non-GOT reference in a PIC object or PLT isn't used. */ |
| 250 | if (!need_dynreloc || !h->non_got_ref) |
| 251 | *head = NULL; |
| 252 | |
| 253 | readonly_dynrelocs_against_ifunc = FALSE; |
| 254 | |
| 255 | /* Finally, allocate space. */ |
| 256 | p = *head; |
| 257 | if (p != NULL) |
| 258 | { |
| 259 | bfd_size_type count = 0; |
| 260 | do |
| 261 | { |
| 262 | if (!readonly_dynrelocs_against_ifunc) |
| 263 | { |
| 264 | asection *s = p->sec->output_section; |
| 265 | if (s != NULL && (s->flags & SEC_READONLY) != 0) |
| 266 | readonly_dynrelocs_against_ifunc = TRUE; |
| 267 | } |
| 268 | count += p->count; |
| 269 | p = p->next; |
| 270 | } |
| 271 | while (p != NULL); |
| 272 | |
| 273 | /* Dynamic relocations are stored in |
| 274 | 1. .rel[a].ifunc section in PIC object. |
| 275 | 2. .rel[a].got section in dynamic executable. |
| 276 | 3. .rel[a].iplt section in static executable. */ |
| 277 | if (bfd_link_pic (info)) |
| 278 | htab->irelifunc->size += count * sizeof_reloc; |
| 279 | else if (htab->splt != NULL) |
| 280 | htab->srelgot->size += count * sizeof_reloc; |
| 281 | else |
| 282 | { |
| 283 | relplt->size += count * sizeof_reloc; |
| 284 | relplt->reloc_count += count; |
| 285 | } |
| 286 | } |
| 287 | |
| 288 | if (readonly_dynrelocs_against_ifunc_p) |
| 289 | *readonly_dynrelocs_against_ifunc_p = readonly_dynrelocs_against_ifunc; |
| 290 | |
| 291 | /* For STT_GNU_IFUNC symbol, .got.plt has the real function address |
| 292 | and .got has the PLT entry adddress. We will load the GOT entry |
| 293 | with the PLT entry in finish_dynamic_symbol if it is used. For |
| 294 | branch, it uses .got.plt. For symbol value, if PLT is used, |
| 295 | 1. Use .got.plt in a PIC object if it is forced local or not |
| 296 | dynamic. |
| 297 | 2. Use .got.plt in a non-PIC object if pointer equality isn't |
| 298 | needed. |
| 299 | 3. Use .got.plt in PIE. |
| 300 | 4. Use .got.plt if .got isn't used. |
| 301 | 5. Otherwise use .got so that it can be shared among different |
| 302 | objects at run-time. |
| 303 | If PLT isn't used, always use .got for symbol value. |
| 304 | We only need to relocate .got entry in PIC object or in dynamic |
| 305 | executable without PLT. */ |
| 306 | if (use_plt |
| 307 | && (h->got.refcount <= 0 |
| 308 | || (bfd_link_pic (info) |
| 309 | && (h->dynindx == -1 |
| 310 | || h->forced_local)) |
| 311 | || (!bfd_link_pic (info) |
| 312 | && !h->pointer_equality_needed) |
| 313 | || bfd_link_pie (info) |
| 314 | || htab->sgot == NULL)) |
| 315 | { |
| 316 | /* Use .got.plt. */ |
| 317 | h->got.offset = (bfd_vma) -1; |
| 318 | } |
| 319 | else |
| 320 | { |
| 321 | if (!use_plt) |
| 322 | { |
| 323 | /* PLT isn't used. */ |
| 324 | h->plt.offset = (bfd_vma) -1; |
| 325 | } |
| 326 | if (h->got.refcount <= 0) |
| 327 | { |
| 328 | /* GOT isn't need when there are only relocations for static |
| 329 | pointers. */ |
| 330 | h->got.offset = (bfd_vma) -1; |
| 331 | } |
| 332 | else |
| 333 | { |
| 334 | h->got.offset = htab->sgot->size; |
| 335 | htab->sgot->size += got_entry_size; |
| 336 | /* Need to relocate the GOT entry in a PIC object or PLT isn't |
| 337 | used. Otherwise, the GOT entry will be filled with the PLT |
| 338 | entry and dynamic GOT relocation isn't needed. */ |
| 339 | if (need_dynreloc) |
| 340 | { |
| 341 | /* For non-static executable, dynamic GOT relocation is in |
| 342 | .rel[a].got section, but for static executable, it is |
| 343 | in .rel[a].iplt section. */ |
| 344 | if (htab->splt != NULL) |
| 345 | htab->srelgot->size += sizeof_reloc; |
| 346 | else |
| 347 | { |
| 348 | relplt->size += sizeof_reloc; |
| 349 | relplt->reloc_count++; |
| 350 | } |
| 351 | } |
| 352 | } |
| 353 | } |
| 354 | |
| 355 | return TRUE; |
| 356 | } |
| 357 | |
| 358 | /* Similar to _bfd_elf_get_synthetic_symtab, optimized for unsorted PLT |
| 359 | entries. PLT is the PLT section. PLT_SYM_VAL is a function pointer |
| 360 | which returns an array of PLT entry symbol values. */ |
| 361 | |
| 362 | long |
| 363 | _bfd_elf_ifunc_get_synthetic_symtab |
| 364 | (bfd *abfd, long symcount ATTRIBUTE_UNUSED, |
| 365 | asymbol **syms ATTRIBUTE_UNUSED, long dynsymcount, asymbol **dynsyms, |
| 366 | asymbol **ret, asection *plt, |
| 367 | bfd_vma *(*get_plt_sym_val) (bfd *, asymbol **, asection *, asection *)) |
| 368 | { |
| 369 | const struct elf_backend_data *bed = get_elf_backend_data (abfd); |
| 370 | asection *relplt; |
| 371 | asymbol *s; |
| 372 | const char *relplt_name; |
| 373 | bfd_boolean (*slurp_relocs) (bfd *, asection *, asymbol **, bfd_boolean); |
| 374 | arelent *p; |
| 375 | long count, i, n; |
| 376 | size_t size; |
| 377 | Elf_Internal_Shdr *hdr; |
| 378 | char *names; |
| 379 | bfd_vma *plt_sym_val; |
| 380 | |
| 381 | *ret = NULL; |
| 382 | |
| 383 | if (plt == NULL) |
| 384 | return 0; |
| 385 | |
| 386 | if ((abfd->flags & (DYNAMIC | EXEC_P)) == 0) |
| 387 | return 0; |
| 388 | |
| 389 | if (dynsymcount <= 0) |
| 390 | return 0; |
| 391 | |
| 392 | relplt_name = bed->relplt_name; |
| 393 | if (relplt_name == NULL) |
| 394 | relplt_name = bed->rela_plts_and_copies_p ? ".rela.plt" : ".rel.plt"; |
| 395 | relplt = bfd_get_section_by_name (abfd, relplt_name); |
| 396 | if (relplt == NULL) |
| 397 | return 0; |
| 398 | |
| 399 | hdr = &elf_section_data (relplt)->this_hdr; |
| 400 | if (hdr->sh_link != elf_dynsymtab (abfd) |
| 401 | || (hdr->sh_type != SHT_REL && hdr->sh_type != SHT_RELA)) |
| 402 | return 0; |
| 403 | |
| 404 | slurp_relocs = get_elf_backend_data (abfd)->s->slurp_reloc_table; |
| 405 | if (! (*slurp_relocs) (abfd, relplt, dynsyms, TRUE)) |
| 406 | return -1; |
| 407 | |
| 408 | count = relplt->size / hdr->sh_entsize; |
| 409 | size = count * sizeof (asymbol); |
| 410 | p = relplt->relocation; |
| 411 | for (i = 0; i < count; i++, p += bed->s->int_rels_per_ext_rel) |
| 412 | { |
| 413 | size += strlen ((*p->sym_ptr_ptr)->name) + sizeof ("@plt"); |
| 414 | if (p->addend != 0) |
| 415 | { |
| 416 | #ifdef BFD64 |
| 417 | size += sizeof ("+0x") - 1 + 8 + 8 * (bed->s->elfclass == ELFCLASS64); |
| 418 | #else |
| 419 | size += sizeof ("+0x") - 1 + 8; |
| 420 | #endif |
| 421 | } |
| 422 | } |
| 423 | |
| 424 | plt_sym_val = get_plt_sym_val (abfd, dynsyms, plt, relplt); |
| 425 | if (plt_sym_val == NULL) |
| 426 | return -1; |
| 427 | |
| 428 | s = *ret = (asymbol *) bfd_malloc (size); |
| 429 | if (s == NULL) |
| 430 | { |
| 431 | free (plt_sym_val); |
| 432 | return -1; |
| 433 | } |
| 434 | |
| 435 | names = (char *) (s + count); |
| 436 | p = relplt->relocation; |
| 437 | n = 0; |
| 438 | for (i = 0; i < count; i++, p += bed->s->int_rels_per_ext_rel) |
| 439 | { |
| 440 | size_t len; |
| 441 | bfd_vma addr; |
| 442 | |
| 443 | addr = plt_sym_val[i]; |
| 444 | if (addr == (bfd_vma) -1) |
| 445 | continue; |
| 446 | |
| 447 | *s = **p->sym_ptr_ptr; |
| 448 | /* Undefined syms won't have BSF_LOCAL or BSF_GLOBAL set. Since |
| 449 | we are defining a symbol, ensure one of them is set. */ |
| 450 | if ((s->flags & BSF_LOCAL) == 0) |
| 451 | s->flags |= BSF_GLOBAL; |
| 452 | s->flags |= BSF_SYNTHETIC; |
| 453 | s->section = plt; |
| 454 | s->value = addr - plt->vma; |
| 455 | s->name = names; |
| 456 | s->udata.p = NULL; |
| 457 | len = strlen ((*p->sym_ptr_ptr)->name); |
| 458 | memcpy (names, (*p->sym_ptr_ptr)->name, len); |
| 459 | names += len; |
| 460 | if (p->addend != 0) |
| 461 | { |
| 462 | char buf[30], *a; |
| 463 | |
| 464 | memcpy (names, "+0x", sizeof ("+0x") - 1); |
| 465 | names += sizeof ("+0x") - 1; |
| 466 | bfd_sprintf_vma (abfd, buf, p->addend); |
| 467 | for (a = buf; *a == '0'; ++a) |
| 468 | ; |
| 469 | len = strlen (a); |
| 470 | memcpy (names, a, len); |
| 471 | names += len; |
| 472 | } |
| 473 | memcpy (names, "@plt", sizeof ("@plt")); |
| 474 | names += sizeof ("@plt"); |
| 475 | ++s, ++n; |
| 476 | } |
| 477 | |
| 478 | free (plt_sym_val); |
| 479 | |
| 480 | return n; |
| 481 | } |