1 /* ELF STT_GNU_IFUNC support. 2 Copyright (C) 2009-2014 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 (info->shared) 57 { 58 /* We need to create .rel[a].ifunc for shared 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 unsigned int plt_entry_size, 114 unsigned int plt_header_size, 115 unsigned int got_entry_size) 116 { 117 asection *plt, *gotplt, *relplt; 118 struct elf_dyn_relocs *p; 119 unsigned int sizeof_reloc; 120 const struct elf_backend_data *bed; 121 struct elf_link_hash_table *htab; 122 123 /* When a shared library references a STT_GNU_IFUNC symbol defined 124 in executable, the address of the resolved function may be used. 125 But in non-shared executable, the address of its .plt slot may 126 be used. Pointer equality may not work correctly. PIE should 127 be used if pointer equality is required here. */ 128 if (!info->shared 129 && (h->dynindx != -1 130 || info->export_dynamic) 131 && h->pointer_equality_needed) 132 { 133 info->callbacks->einfo 134 (_("%F%P: dynamic STT_GNU_IFUNC symbol `%s' with pointer " 135 "equality in `%B' can not be used when making an " 136 "executable; recompile with -fPIE and relink with -pie\n"), 137 h->root.root.string, 138 h->root.u.def.section->owner); 139 bfd_set_error (bfd_error_bad_value); 140 return FALSE; 141 } 142 143 htab = elf_hash_table (info); 144 145 /* When building shared library, we need to handle the case where it is 146 marked with regular reference, but not non-GOT reference since the 147 non-GOT reference bit may not be set here. */ 148 if (info->shared && !h->non_got_ref && h->ref_regular) 149 for (p = *head; p != NULL; p = p->next) 150 if (p->count) 151 { 152 h->non_got_ref = 1; 153 goto keep; 154 } 155 156 /* Support garbage collection against STT_GNU_IFUNC symbols. */ 157 if (h->plt.refcount <= 0 && h->got.refcount <= 0) 158 { 159 h->got = htab->init_got_offset; 160 h->plt = htab->init_plt_offset; 161 *head = NULL; 162 return TRUE; 163 } 164 165 /* Return and discard space for dynamic relocations against it if 166 it is never referenced in a non-shared object. */ 167 if (!h->ref_regular) 168 { 169 if (h->plt.refcount > 0 170 || h->got.refcount > 0) 171 abort (); 172 h->got = htab->init_got_offset; 173 h->plt = htab->init_plt_offset; 174 *head = NULL; 175 return TRUE; 176 } 177 178 keep: 179 bed = get_elf_backend_data (info->output_bfd); 180 if (bed->rela_plts_and_copies_p) 181 sizeof_reloc = bed->s->sizeof_rela; 182 else 183 sizeof_reloc = bed->s->sizeof_rel; 184 185 /* When building a static executable, use .iplt, .igot.plt and 186 .rel[a].iplt sections for STT_GNU_IFUNC symbols. */ 187 if (htab->splt != NULL) 188 { 189 plt = htab->splt; 190 gotplt = htab->sgotplt; 191 relplt = htab->srelplt; 192 193 /* If this is the first .plt entry, make room for the special 194 first entry. */ 195 if (plt->size == 0) 196 plt->size += plt_header_size; 197 } 198 else 199 { 200 plt = htab->iplt; 201 gotplt = htab->igotplt; 202 relplt = htab->irelplt; 203 } 204 205 /* Don't update value of STT_GNU_IFUNC symbol to PLT. We need 206 the original value for R_*_IRELATIVE. */ 207 h->plt.offset = plt->size; 208 209 /* Make room for this entry in the .plt/.iplt section. */ 210 plt->size += plt_entry_size; 211 212 /* We also need to make an entry in the .got.plt/.got.iplt section, 213 which will be placed in the .got section by the linker script. */ 214 gotplt->size += got_entry_size; 215 216 /* We also need to make an entry in the .rel[a].plt/.rel[a].iplt 217 section. */ 218 relplt->size += sizeof_reloc; 219 relplt->reloc_count++; 220 221 /* We need dynamic relocation for STT_GNU_IFUNC symbol only when 222 there is a non-GOT reference in a shared object. */ 223 if (!info->shared 224 || !h->non_got_ref) 225 *head = NULL; 226 227 /* Finally, allocate space. */ 228 p = *head; 229 if (p != NULL) 230 { 231 bfd_size_type count = 0; 232 do 233 { 234 count += p->count; 235 p = p->next; 236 } 237 while (p != NULL); 238 htab->irelifunc->size += count * sizeof_reloc; 239 } 240 241 /* For STT_GNU_IFUNC symbol, .got.plt has the real function address 242 and .got has the PLT entry adddress. We will load the GOT entry 243 with the PLT entry in finish_dynamic_symbol if it is used. For 244 branch, it uses .got.plt. For symbol value, 245 1. Use .got.plt in a shared object if it is forced local or not 246 dynamic. 247 2. Use .got.plt in a non-shared object if pointer equality isn't 248 needed. 249 3. Use .got.plt in PIE. 250 4. Use .got.plt if .got isn't used. 251 5. Otherwise use .got so that it can be shared among different 252 objects at run-time. 253 We only need to relocate .got entry in shared object. */ 254 if (h->got.refcount <= 0 255 || (info->shared 256 && (h->dynindx == -1 257 || h->forced_local)) 258 || (!info->shared 259 && !h->pointer_equality_needed) 260 || (info->executable && info->shared) 261 || htab->sgot == NULL) 262 { 263 /* Use .got.plt. */ 264 h->got.offset = (bfd_vma) -1; 265 } 266 else 267 { 268 h->got.offset = htab->sgot->size; 269 htab->sgot->size += got_entry_size; 270 if (info->shared) 271 htab->srelgot->size += sizeof_reloc; 272 } 273 274 return TRUE; 275 } 276
