| 1 | /* ELF STT_GNU_IFUNC support. |
| 2 | Copyright 2009 |
| 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 "bfdlink.h" |
| 25 | #include "libbfd.h" |
| 26 | #define ARCH_SIZE 0 |
| 27 | #include "elf-bfd.h" |
| 28 | #include "safe-ctype.h" |
| 29 | #include "libiberty.h" |
| 30 | #include "objalloc.h" |
| 31 | |
| 32 | /* Create sections needed by STT_GNU_IFUNC symbol. */ |
| 33 | |
| 34 | bfd_boolean |
| 35 | _bfd_elf_create_ifunc_sections (bfd *abfd, struct bfd_link_info *info) |
| 36 | { |
| 37 | flagword flags, pltflags; |
| 38 | asection *s; |
| 39 | const struct elf_backend_data *bed = get_elf_backend_data (abfd); |
| 40 | struct elf_link_hash_table *htab = elf_hash_table (info); |
| 41 | |
| 42 | if (htab->irelifunc != NULL || htab->iplt != NULL) |
| 43 | return TRUE; |
| 44 | |
| 45 | flags = bed->dynamic_sec_flags; |
| 46 | pltflags = flags; |
| 47 | if (bed->plt_not_loaded) |
| 48 | /* We do not clear SEC_ALLOC here because we still want the OS to |
| 49 | allocate space for the section; it's just that there's nothing |
| 50 | to read in from the object file. */ |
| 51 | pltflags &= ~ (SEC_CODE | SEC_LOAD | SEC_HAS_CONTENTS); |
| 52 | else |
| 53 | pltflags |= SEC_ALLOC | SEC_CODE | SEC_LOAD; |
| 54 | if (bed->plt_readonly) |
| 55 | pltflags |= SEC_READONLY; |
| 56 | |
| 57 | if (info->shared) |
| 58 | { |
| 59 | /* We need to create .rel[a].ifunc for shared objects. */ |
| 60 | const char *rel_sec = (bed->rela_plts_and_copies_p |
| 61 | ? ".rela.ifunc" : ".rel.ifunc"); |
| 62 | |
| 63 | s = bfd_make_section_with_flags (abfd, rel_sec, |
| 64 | flags | SEC_READONLY); |
| 65 | if (s == NULL |
| 66 | || ! bfd_set_section_alignment (abfd, s, |
| 67 | bed->s->log_file_align)) |
| 68 | return FALSE; |
| 69 | htab->irelifunc = s; |
| 70 | } |
| 71 | else |
| 72 | { |
| 73 | /* We need to create .iplt, .rel[a].iplt, .igot and .igot.plt |
| 74 | for static executables. */ |
| 75 | s = bfd_make_section_with_flags (abfd, ".iplt", pltflags); |
| 76 | if (s == NULL |
| 77 | || ! bfd_set_section_alignment (abfd, s, bed->plt_alignment)) |
| 78 | return FALSE; |
| 79 | htab->iplt = s; |
| 80 | |
| 81 | s = bfd_make_section_with_flags (abfd, |
| 82 | (bed->rela_plts_and_copies_p |
| 83 | ? ".rela.iplt" : ".rel.iplt"), |
| 84 | flags | SEC_READONLY); |
| 85 | if (s == NULL |
| 86 | || ! bfd_set_section_alignment (abfd, s, |
| 87 | bed->s->log_file_align)) |
| 88 | return FALSE; |
| 89 | htab->irelplt = s; |
| 90 | |
| 91 | /* We don't need the .igot section if we have the .igot.plt |
| 92 | section. */ |
| 93 | if (bed->want_got_plt) |
| 94 | s = bfd_make_section_with_flags (abfd, ".igot.plt", flags); |
| 95 | else |
| 96 | s = bfd_make_section_with_flags (abfd, ".igot", flags); |
| 97 | if (s == NULL |
| 98 | || !bfd_set_section_alignment (abfd, s, |
| 99 | bed->s->log_file_align)) |
| 100 | return FALSE; |
| 101 | htab->igotplt = s; |
| 102 | } |
| 103 | |
| 104 | return TRUE; |
| 105 | } |
| 106 | |
| 107 | /* For a STT_GNU_IFUNC symbol, create a dynamic reloc section, SRELOC, |
| 108 | for the input section, SEC, and append this reloc to HEAD. */ |
| 109 | |
| 110 | asection * |
| 111 | _bfd_elf_create_ifunc_dyn_reloc (bfd *abfd, struct bfd_link_info *info, |
| 112 | asection *sec, asection *sreloc, |
| 113 | struct elf_dyn_relocs **head) |
| 114 | { |
| 115 | struct elf_dyn_relocs *p; |
| 116 | struct elf_link_hash_table *htab = elf_hash_table (info); |
| 117 | |
| 118 | if (sreloc == NULL) |
| 119 | { |
| 120 | const struct elf_backend_data *bed = get_elf_backend_data (abfd); |
| 121 | |
| 122 | if (htab->dynobj == NULL) |
| 123 | htab->dynobj = abfd; |
| 124 | |
| 125 | sreloc = _bfd_elf_make_dynamic_reloc_section (sec, htab->dynobj, |
| 126 | bed->s->log_file_align, |
| 127 | abfd, |
| 128 | bed->rela_plts_and_copies_p); |
| 129 | if (sreloc == NULL) |
| 130 | return NULL; |
| 131 | } |
| 132 | |
| 133 | p = *head; |
| 134 | if (p == NULL || p->sec != sec) |
| 135 | { |
| 136 | bfd_size_type amt = sizeof *p; |
| 137 | |
| 138 | p = ((struct elf_dyn_relocs *) bfd_alloc (htab->dynobj, amt)); |
| 139 | if (p == NULL) |
| 140 | return NULL; |
| 141 | p->next = *head; |
| 142 | *head = p; |
| 143 | p->sec = sec; |
| 144 | p->count = 0; |
| 145 | p->pc_count = 0; |
| 146 | } |
| 147 | p->count += 1; |
| 148 | |
| 149 | return sreloc; |
| 150 | } |
| 151 | |
| 152 | /* Allocate space in .plt, .got and associated reloc sections for |
| 153 | dynamic relocs against a STT_GNU_IFUNC symbol definition. */ |
| 154 | |
| 155 | bfd_boolean |
| 156 | _bfd_elf_allocate_ifunc_dyn_relocs (struct bfd_link_info *info, |
| 157 | struct elf_link_hash_entry *h, |
| 158 | struct elf_dyn_relocs **head, |
| 159 | unsigned int plt_entry_size, |
| 160 | unsigned int got_entry_size) |
| 161 | { |
| 162 | asection *plt, *gotplt, *relplt; |
| 163 | struct elf_dyn_relocs *p; |
| 164 | unsigned int sizeof_reloc; |
| 165 | const struct elf_backend_data *bed; |
| 166 | struct elf_link_hash_table *htab; |
| 167 | |
| 168 | /* When a shared library references a STT_GNU_IFUNC symbol defined |
| 169 | in executable, the address of the resolved function may be used. |
| 170 | But in non-shared executable, the address of its .plt slot may |
| 171 | be used. Pointer equality may not work correctly. PIE should |
| 172 | be used if pointer equality is required here. */ |
| 173 | if (!info->shared |
| 174 | && (h->dynindx != -1 |
| 175 | || info->export_dynamic) |
| 176 | && h->pointer_equality_needed) |
| 177 | { |
| 178 | info->callbacks->einfo |
| 179 | (_("%F%P: dynamic STT_GNU_IFUNC symbol `%s' with pointer " |
| 180 | "equality in `%B' can not be used when making an " |
| 181 | "executable; recompile with -fPIE and relink with -pie\n"), |
| 182 | h->root.root.string, |
| 183 | h->root.u.def.section->owner); |
| 184 | bfd_set_error (bfd_error_bad_value); |
| 185 | return FALSE; |
| 186 | } |
| 187 | |
| 188 | htab = elf_hash_table (info); |
| 189 | |
| 190 | /* Support garbage collection against STT_GNU_IFUNC symbols. */ |
| 191 | if (h->plt.refcount <= 0 && h->got.refcount <= 0) |
| 192 | { |
| 193 | h->got = htab->init_got_offset; |
| 194 | h->plt = htab->init_plt_offset; |
| 195 | *head = NULL; |
| 196 | return TRUE; |
| 197 | } |
| 198 | |
| 199 | /* Return and discard space for dynamic relocations against it if |
| 200 | it is never referenced in a non-shared object. */ |
| 201 | if (!h->ref_regular) |
| 202 | { |
| 203 | if (h->plt.refcount > 0 |
| 204 | || h->got.refcount > 0) |
| 205 | abort (); |
| 206 | h->got = htab->init_got_offset; |
| 207 | h->plt = htab->init_plt_offset; |
| 208 | *head = NULL; |
| 209 | return TRUE; |
| 210 | } |
| 211 | |
| 212 | bed = get_elf_backend_data (info->output_bfd); |
| 213 | if (bed->rela_plts_and_copies_p) |
| 214 | sizeof_reloc = bed->s->sizeof_rela; |
| 215 | else |
| 216 | sizeof_reloc = bed->s->sizeof_rel; |
| 217 | |
| 218 | /* When building a static executable, use .iplt, .igot.plt and |
| 219 | .rel[a].iplt sections for STT_GNU_IFUNC symbols. */ |
| 220 | if (htab->splt != NULL) |
| 221 | { |
| 222 | plt = htab->splt; |
| 223 | gotplt = htab->sgotplt; |
| 224 | relplt = htab->srelplt; |
| 225 | |
| 226 | /* If this is the first .plt entry, make room for the special |
| 227 | first entry. */ |
| 228 | if (plt->size == 0) |
| 229 | plt->size += plt_entry_size; |
| 230 | } |
| 231 | else |
| 232 | { |
| 233 | plt = htab->iplt; |
| 234 | gotplt = htab->igotplt; |
| 235 | relplt = htab->irelplt; |
| 236 | } |
| 237 | |
| 238 | /* Don't update value of STT_GNU_IFUNC symbol to PLT. We need |
| 239 | the original value for R_*_IRELATIVE. */ |
| 240 | h->plt.offset = plt->size; |
| 241 | |
| 242 | /* Make room for this entry in the .plt/.iplt section. */ |
| 243 | plt->size += plt_entry_size; |
| 244 | |
| 245 | /* We also need to make an entry in the .got.plt/.got.iplt section, |
| 246 | which will be placed in the .got section by the linker script. */ |
| 247 | gotplt->size += got_entry_size; |
| 248 | |
| 249 | /* We also need to make an entry in the .rel[a].plt/.rel[a].iplt |
| 250 | section. */ |
| 251 | relplt->size += sizeof_reloc; |
| 252 | relplt->reloc_count++; |
| 253 | |
| 254 | /* We need dynamic relocation for STT_GNU_IFUNC symbol only when |
| 255 | there is a non-GOT reference in a shared object. */ |
| 256 | if (!info->shared |
| 257 | || !h->non_got_ref) |
| 258 | *head = NULL; |
| 259 | |
| 260 | /* Finally, allocate space. */ |
| 261 | for (p = *head; p != NULL; p = p->next) |
| 262 | htab->irelifunc->size += p->count * sizeof_reloc; |
| 263 | |
| 264 | /* For STT_GNU_IFUNC symbol, .got.plt has the real function addres |
| 265 | and .got has the PLT entry adddress. We will load the GOT entry |
| 266 | with the PLT entry in finish_dynamic_symbol if it is used. For |
| 267 | branch, it uses .got.plt. For symbol value, |
| 268 | 1. Use .got.plt in a shared object if it is forced local or not |
| 269 | dynamic. |
| 270 | 2. Use .got.plt in a non-shared object if pointer equality isn't |
| 271 | needed. |
| 272 | 3. Use .got.plt in PIE. |
| 273 | 4. Use .got.plt if .got isn't used. |
| 274 | 5. Otherwise use .got so that it can be shared among different |
| 275 | objects at run-time. |
| 276 | We only need to relocate .got entry in shared object. */ |
| 277 | if ((info->shared |
| 278 | && (h->dynindx == -1 |
| 279 | || h->forced_local)) |
| 280 | || (!info->shared |
| 281 | && !h->pointer_equality_needed) |
| 282 | || (info->executable && info->shared) |
| 283 | || htab->sgot == NULL) |
| 284 | { |
| 285 | /* Use .got.plt. */ |
| 286 | h->got.offset = (bfd_vma) -1; |
| 287 | } |
| 288 | else |
| 289 | { |
| 290 | h->got.offset = htab->sgot->size; |
| 291 | htab->sgot->size += got_entry_size; |
| 292 | if (info->shared) |
| 293 | htab->srelgot->size += sizeof_reloc; |
| 294 | } |
| 295 | |
| 296 | return TRUE; |
| 297 | } |