1 /* ELF STT_GNU_IFUNC support. 2 Copyright 2009-2013 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 /* Allocate space in .plt, .got and associated reloc sections for 108 dynamic relocs against a STT_GNU_IFUNC symbol definition. */ 109 110 bfd_boolean 111 _bfd_elf_allocate_ifunc_dyn_relocs (struct bfd_link_info *info, 112 struct elf_link_hash_entry *h, 113 struct elf_dyn_relocs **head, 114 unsigned int plt_entry_size, 115 unsigned int plt_header_size, 116 unsigned int got_entry_size) 117 { 118 asection *plt, *gotplt, *relplt; 119 struct elf_dyn_relocs *p; 120 unsigned int sizeof_reloc; 121 const struct elf_backend_data *bed; 122 struct elf_link_hash_table *htab; 123 124 /* When a shared library references a STT_GNU_IFUNC symbol defined 125 in executable, the address of the resolved function may be used. 126 But in non-shared executable, the address of its .plt slot may 127 be used. Pointer equality may not work correctly. PIE should 128 be used if pointer equality is required here. */ 129 if (!info->shared 130 && (h->dynindx != -1 131 || info->export_dynamic) 132 && h->pointer_equality_needed) 133 { 134 info->callbacks->einfo 135 (_("%F%P: dynamic STT_GNU_IFUNC symbol `%s' with pointer " 136 "equality in `%B' can not be used when making an " 137 "executable; recompile with -fPIE and relink with -pie\n"), 138 h->root.root.string, 139 h->root.u.def.section->owner); 140 bfd_set_error (bfd_error_bad_value); 141 return FALSE; 142 } 143 144 htab = elf_hash_table (info); 145 146 /* When building shared library, we need to handle the case where it is 147 marked with regular reference, but not non-GOT reference since the 148 non-GOT reference bit may not be set here. */ 149 if (info->shared && !h->non_got_ref && h->ref_regular) 150 for (p = *head; p != NULL; p = p->next) 151 if (p->count) 152 { 153 h->non_got_ref = 1; 154 goto keep; 155 } 156 157 /* Support garbage collection against STT_GNU_IFUNC symbols. */ 158 if (h->plt.refcount <= 0 && h->got.refcount <= 0) 159 { 160 h->got = htab->init_got_offset; 161 h->plt = htab->init_plt_offset; 162 *head = NULL; 163 return TRUE; 164 } 165 166 /* Return and discard space for dynamic relocations against it if 167 it is never referenced in a non-shared object. */ 168 if (!h->ref_regular) 169 { 170 if (h->plt.refcount > 0 171 || h->got.refcount > 0) 172 abort (); 173 h->got = htab->init_got_offset; 174 h->plt = htab->init_plt_offset; 175 *head = NULL; 176 return TRUE; 177 } 178 179 keep: 180 bed = get_elf_backend_data (info->output_bfd); 181 if (bed->rela_plts_and_copies_p) 182 sizeof_reloc = bed->s->sizeof_rela; 183 else 184 sizeof_reloc = bed->s->sizeof_rel; 185 186 /* When building a static executable, use .iplt, .igot.plt and 187 .rel[a].iplt sections for STT_GNU_IFUNC symbols. */ 188 if (htab->splt != NULL) 189 { 190 plt = htab->splt; 191 gotplt = htab->sgotplt; 192 relplt = htab->srelplt; 193 194 /* If this is the first .plt entry, make room for the special 195 first entry. */ 196 if (plt->size == 0) 197 plt->size += plt_header_size; 198 } 199 else 200 { 201 plt = htab->iplt; 202 gotplt = htab->igotplt; 203 relplt = htab->irelplt; 204 } 205 206 /* Don't update value of STT_GNU_IFUNC symbol to PLT. We need 207 the original value for R_*_IRELATIVE. */ 208 h->plt.offset = plt->size; 209 210 /* Make room for this entry in the .plt/.iplt section. */ 211 plt->size += plt_entry_size; 212 213 /* We also need to make an entry in the .got.plt/.got.iplt section, 214 which will be placed in the .got section by the linker script. */ 215 gotplt->size += got_entry_size; 216 217 /* We also need to make an entry in the .rel[a].plt/.rel[a].iplt 218 section. */ 219 relplt->size += sizeof_reloc; 220 relplt->reloc_count++; 221 222 /* We need dynamic relocation for STT_GNU_IFUNC symbol only when 223 there is a non-GOT reference in a shared object. */ 224 if (!info->shared 225 || !h->non_got_ref) 226 *head = NULL; 227 228 /* Finally, allocate space. */ 229 p = *head; 230 if (p != NULL) 231 { 232 bfd_size_type count = 0; 233 do 234 { 235 count += p->count; 236 p = p->next; 237 } 238 while (p != NULL); 239 htab->irelifunc->size += count * sizeof_reloc; 240 } 241 242 /* For STT_GNU_IFUNC symbol, .got.plt has the real function address 243 and .got has the PLT entry adddress. We will load the GOT entry 244 with the PLT entry in finish_dynamic_symbol if it is used. For 245 branch, it uses .got.plt. For symbol value, 246 1. Use .got.plt in a shared object if it is forced local or not 247 dynamic. 248 2. Use .got.plt in a non-shared object if pointer equality isn't 249 needed. 250 3. Use .got.plt in PIE. 251 4. Use .got.plt if .got isn't used. 252 5. Otherwise use .got so that it can be shared among different 253 objects at run-time. 254 We only need to relocate .got entry in shared object. */ 255 if (h->got.refcount <= 0 256 || (info->shared 257 && (h->dynindx == -1 258 || h->forced_local)) 259 || (!info->shared 260 && !h->pointer_equality_needed) 261 || (info->executable && info->shared) 262 || htab->sgot == NULL) 263 { 264 /* Use .got.plt. */ 265 h->got.offset = (bfd_vma) -1; 266 } 267 else 268 { 269 h->got.offset = htab->sgot->size; 270 htab->sgot->size += got_entry_size; 271 if (info->shared) 272 htab->srelgot->size += sizeof_reloc; 273 } 274 275 return TRUE; 276 } 277