| 1 | /* ELF STT_GNU_IFUNC support. |
| 2 | Copyright (C) 2009-2019 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 (s, bed->s->log_file_align)) |
| 66 | return FALSE; |
| 67 | htab->irelifunc = s; |
| 68 | } |
| 69 | else |
| 70 | { |
| 71 | /* We need to create .iplt, .rel[a].iplt, .igot and .igot.plt |
| 72 | for static executables. */ |
| 73 | s = bfd_make_section_with_flags (abfd, ".iplt", pltflags); |
| 74 | if (s == NULL |
| 75 | || !bfd_set_section_alignment (s, bed->plt_alignment)) |
| 76 | return FALSE; |
| 77 | htab->iplt = s; |
| 78 | |
| 79 | s = bfd_make_section_with_flags (abfd, |
| 80 | (bed->rela_plts_and_copies_p |
| 81 | ? ".rela.iplt" : ".rel.iplt"), |
| 82 | flags | SEC_READONLY); |
| 83 | if (s == NULL |
| 84 | || !bfd_set_section_alignment (s, bed->s->log_file_align)) |
| 85 | return FALSE; |
| 86 | htab->irelplt = s; |
| 87 | |
| 88 | /* We don't need the .igot section if we have the .igot.plt |
| 89 | section. */ |
| 90 | if (bed->want_got_plt) |
| 91 | s = bfd_make_section_with_flags (abfd, ".igot.plt", flags); |
| 92 | else |
| 93 | s = bfd_make_section_with_flags (abfd, ".igot", flags); |
| 94 | if (s == NULL |
| 95 | || !bfd_set_section_alignment (s, bed->s->log_file_align)) |
| 96 | return FALSE; |
| 97 | htab->igotplt = s; |
| 98 | } |
| 99 | |
| 100 | return TRUE; |
| 101 | } |
| 102 | |
| 103 | /* Allocate space in .plt, .got and associated reloc sections for |
| 104 | dynamic relocs against a STT_GNU_IFUNC symbol definition. */ |
| 105 | |
| 106 | bfd_boolean |
| 107 | _bfd_elf_allocate_ifunc_dyn_relocs (struct bfd_link_info *info, |
| 108 | struct elf_link_hash_entry *h, |
| 109 | struct elf_dyn_relocs **head, |
| 110 | bfd_boolean *readonly_dynrelocs_against_ifunc_p, |
| 111 | unsigned int plt_entry_size, |
| 112 | unsigned int plt_header_size, |
| 113 | unsigned int got_entry_size, |
| 114 | bfd_boolean avoid_plt) |
| 115 | { |
| 116 | asection *plt, *gotplt, *relplt; |
| 117 | struct elf_dyn_relocs *p; |
| 118 | unsigned int sizeof_reloc; |
| 119 | const struct elf_backend_data *bed; |
| 120 | struct elf_link_hash_table *htab; |
| 121 | bfd_boolean readonly_dynrelocs_against_ifunc; |
| 122 | /* If AVOID_PLT is TRUE, don't use PLT if possible. */ |
| 123 | bfd_boolean use_plt = !avoid_plt || h->plt.refcount > 0; |
| 124 | bfd_boolean need_dynreloc = !use_plt || bfd_link_pic (info); |
| 125 | |
| 126 | /* When a PIC object references a STT_GNU_IFUNC symbol defined |
| 127 | in executable or it isn't referenced via PLT, the address of |
| 128 | the resolved function may be used. But in non-PIC executable, |
| 129 | the address of its .plt slot may be used. Pointer equality may |
| 130 | not work correctly. PIE or non-PLT reference should be used if |
| 131 | pointer equality is required here. |
| 132 | |
| 133 | If STT_GNU_IFUNC symbol is defined in position-dependent executable, |
| 134 | backend should change it to the normal function and set its address |
| 135 | to its PLT entry which should be resolved by R_*_IRELATIVE at |
| 136 | run-time. All external references should be resolved to its PLT in |
| 137 | executable. */ |
| 138 | if (!need_dynreloc |
| 139 | && !(bfd_link_pde (info) && h->def_regular) |
| 140 | && (h->dynindx != -1 |
| 141 | || info->export_dynamic) |
| 142 | && h->pointer_equality_needed) |
| 143 | { |
| 144 | info->callbacks->einfo |
| 145 | /* xgettext:c-format */ |
| 146 | (_("%F%P: dynamic STT_GNU_IFUNC symbol `%s' with pointer " |
| 147 | "equality in `%pB' can not be used when making an " |
| 148 | "executable; recompile with -fPIE and relink with -pie\n"), |
| 149 | h->root.root.string, |
| 150 | h->root.u.def.section->owner); |
| 151 | bfd_set_error (bfd_error_bad_value); |
| 152 | return FALSE; |
| 153 | } |
| 154 | |
| 155 | htab = elf_hash_table (info); |
| 156 | |
| 157 | /* When the symbol is marked with regular reference, if PLT isn't used |
| 158 | or we are building a PIC object, we must keep dynamic relocation |
| 159 | if there is non-GOT reference and use PLT if there is PC-relative |
| 160 | reference. */ |
| 161 | if (need_dynreloc && h->ref_regular) |
| 162 | { |
| 163 | bfd_boolean keep = FALSE; |
| 164 | for (p = *head; p != NULL; p = p->next) |
| 165 | if (p->count) |
| 166 | { |
| 167 | h->non_got_ref = 1; |
| 168 | /* Need dynamic relocations for non-GOT reference. */ |
| 169 | keep = TRUE; |
| 170 | if (p->pc_count) |
| 171 | { |
| 172 | /* Must use PLT for PC-relative reference. */ |
| 173 | use_plt = TRUE; |
| 174 | need_dynreloc = bfd_link_pic (info); |
| 175 | break; |
| 176 | } |
| 177 | } |
| 178 | if (keep) |
| 179 | goto keep; |
| 180 | } |
| 181 | |
| 182 | /* Support garbage collection against STT_GNU_IFUNC symbols. */ |
| 183 | if (h->plt.refcount <= 0 && h->got.refcount <= 0) |
| 184 | { |
| 185 | h->got = htab->init_got_offset; |
| 186 | h->plt = htab->init_plt_offset; |
| 187 | *head = NULL; |
| 188 | return TRUE; |
| 189 | } |
| 190 | |
| 191 | /* Return and discard space for dynamic relocations against it if |
| 192 | it is never referenced. */ |
| 193 | if (!h->ref_regular) |
| 194 | { |
| 195 | if (h->plt.refcount > 0 |
| 196 | || h->got.refcount > 0) |
| 197 | abort (); |
| 198 | h->got = htab->init_got_offset; |
| 199 | h->plt = htab->init_plt_offset; |
| 200 | *head = NULL; |
| 201 | return TRUE; |
| 202 | } |
| 203 | |
| 204 | keep: |
| 205 | bed = get_elf_backend_data (info->output_bfd); |
| 206 | if (bed->rela_plts_and_copies_p) |
| 207 | sizeof_reloc = bed->s->sizeof_rela; |
| 208 | else |
| 209 | sizeof_reloc = bed->s->sizeof_rel; |
| 210 | |
| 211 | /* When building a static executable, use .iplt, .igot.plt and |
| 212 | .rel[a].iplt sections for STT_GNU_IFUNC symbols. */ |
| 213 | if (htab->splt != NULL) |
| 214 | { |
| 215 | plt = htab->splt; |
| 216 | gotplt = htab->sgotplt; |
| 217 | relplt = htab->srelplt; |
| 218 | |
| 219 | /* If this is the first .plt entry and PLT is used, make room for |
| 220 | the special first entry. */ |
| 221 | if (plt->size == 0 && use_plt) |
| 222 | plt->size += plt_header_size; |
| 223 | } |
| 224 | else |
| 225 | { |
| 226 | plt = htab->iplt; |
| 227 | gotplt = htab->igotplt; |
| 228 | relplt = htab->irelplt; |
| 229 | } |
| 230 | |
| 231 | if (use_plt) |
| 232 | { |
| 233 | /* Don't update value of STT_GNU_IFUNC symbol to PLT. We need |
| 234 | the original value for R_*_IRELATIVE. */ |
| 235 | h->plt.offset = plt->size; |
| 236 | |
| 237 | /* Make room for this entry in the .plt/.iplt section. */ |
| 238 | plt->size += plt_entry_size; |
| 239 | |
| 240 | /* We also need to make an entry in the .got.plt/.got.iplt section, |
| 241 | which will be placed in the .got section by the linker script. */ |
| 242 | gotplt->size += got_entry_size; |
| 243 | } |
| 244 | |
| 245 | /* We also need to make an entry in the .rel[a].plt/.rel[a].iplt |
| 246 | section for GOTPLT relocation if PLT is used. */ |
| 247 | if (use_plt) |
| 248 | { |
| 249 | relplt->size += sizeof_reloc; |
| 250 | relplt->reloc_count++; |
| 251 | } |
| 252 | |
| 253 | /* We need dynamic relocation for STT_GNU_IFUNC symbol only when |
| 254 | there is a non-GOT reference in a PIC object or PLT isn't used. */ |
| 255 | if (!need_dynreloc || !h->non_got_ref) |
| 256 | *head = NULL; |
| 257 | |
| 258 | readonly_dynrelocs_against_ifunc = FALSE; |
| 259 | |
| 260 | /* Finally, allocate space. */ |
| 261 | p = *head; |
| 262 | if (p != NULL) |
| 263 | { |
| 264 | bfd_size_type count = 0; |
| 265 | do |
| 266 | { |
| 267 | if (!readonly_dynrelocs_against_ifunc) |
| 268 | { |
| 269 | asection *s = p->sec->output_section; |
| 270 | if (s != NULL && (s->flags & SEC_READONLY) != 0) |
| 271 | readonly_dynrelocs_against_ifunc = TRUE; |
| 272 | } |
| 273 | count += p->count; |
| 274 | p = p->next; |
| 275 | } |
| 276 | while (p != NULL); |
| 277 | |
| 278 | /* Dynamic relocations are stored in |
| 279 | 1. .rel[a].ifunc section in PIC object. |
| 280 | 2. .rel[a].got section in dynamic executable. |
| 281 | 3. .rel[a].iplt section in static executable. */ |
| 282 | if (bfd_link_pic (info)) |
| 283 | htab->irelifunc->size += count * sizeof_reloc; |
| 284 | else if (htab->splt != NULL) |
| 285 | htab->srelgot->size += count * sizeof_reloc; |
| 286 | else |
| 287 | { |
| 288 | relplt->size += count * sizeof_reloc; |
| 289 | relplt->reloc_count += count; |
| 290 | } |
| 291 | } |
| 292 | |
| 293 | if (readonly_dynrelocs_against_ifunc_p) |
| 294 | *readonly_dynrelocs_against_ifunc_p = readonly_dynrelocs_against_ifunc; |
| 295 | |
| 296 | /* For STT_GNU_IFUNC symbol, .got.plt has the real function address |
| 297 | and .got has the PLT entry adddress. We will load the GOT entry |
| 298 | with the PLT entry in finish_dynamic_symbol if it is used. For |
| 299 | branch, it uses .got.plt. For symbol value, if PLT is used, |
| 300 | 1. Use .got.plt in a PIC object if it is forced local or not |
| 301 | dynamic. |
| 302 | 2. Use .got.plt in a non-PIC object if pointer equality isn't |
| 303 | needed. |
| 304 | 3. Use .got.plt in PIE. |
| 305 | 4. Use .got.plt if .got isn't used. |
| 306 | 5. Otherwise use .got so that it can be shared among different |
| 307 | objects at run-time. |
| 308 | If PLT isn't used, always use .got for symbol value. |
| 309 | We only need to relocate .got entry in PIC object or in dynamic |
| 310 | executable without PLT. */ |
| 311 | if (use_plt |
| 312 | && (h->got.refcount <= 0 |
| 313 | || (bfd_link_pic (info) |
| 314 | && (h->dynindx == -1 |
| 315 | || h->forced_local)) |
| 316 | || (!bfd_link_pic (info) |
| 317 | && !h->pointer_equality_needed) |
| 318 | || bfd_link_pie (info) |
| 319 | || htab->sgot == NULL)) |
| 320 | { |
| 321 | /* Use .got.plt. */ |
| 322 | h->got.offset = (bfd_vma) -1; |
| 323 | } |
| 324 | else |
| 325 | { |
| 326 | if (!use_plt) |
| 327 | { |
| 328 | /* PLT isn't used. */ |
| 329 | h->plt.offset = (bfd_vma) -1; |
| 330 | } |
| 331 | if (h->got.refcount <= 0) |
| 332 | { |
| 333 | /* GOT isn't need when there are only relocations for static |
| 334 | pointers. */ |
| 335 | h->got.offset = (bfd_vma) -1; |
| 336 | } |
| 337 | else |
| 338 | { |
| 339 | h->got.offset = htab->sgot->size; |
| 340 | htab->sgot->size += got_entry_size; |
| 341 | /* Need to relocate the GOT entry in a PIC object or PLT isn't |
| 342 | used. Otherwise, the GOT entry will be filled with the PLT |
| 343 | entry and dynamic GOT relocation isn't needed. */ |
| 344 | if (need_dynreloc) |
| 345 | { |
| 346 | /* For non-static executable, dynamic GOT relocation is in |
| 347 | .rel[a].got section, but for static executable, it is |
| 348 | in .rel[a].iplt section. */ |
| 349 | if (htab->splt != NULL) |
| 350 | htab->srelgot->size += sizeof_reloc; |
| 351 | else |
| 352 | { |
| 353 | relplt->size += sizeof_reloc; |
| 354 | relplt->reloc_count++; |
| 355 | } |
| 356 | } |
| 357 | } |
| 358 | } |
| 359 | |
| 360 | return TRUE; |
| 361 | } |