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6de2ae4a | 1 | /* ELF STT_GNU_IFUNC support. |
b3adc24a | 2 | Copyright (C) 2009-2020 Free Software Foundation, Inc. |
6de2ae4a L |
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 | ||
0e1862bb | 56 | if (bfd_link_pic (info)) |
6de2ae4a | 57 | { |
233cc9c1 | 58 | /* We need to create .rel[a].ifunc for PIC objects. */ |
6de2ae4a L |
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 | |
fd361982 | 65 | || !bfd_set_section_alignment (s, bed->s->log_file_align)) |
6de2ae4a L |
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 | |
fd361982 | 75 | || !bfd_set_section_alignment (s, bed->plt_alignment)) |
6de2ae4a L |
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 | |
fd361982 | 84 | || !bfd_set_section_alignment (s, bed->s->log_file_align)) |
6de2ae4a L |
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 | |
fd361982 | 95 | || !bfd_set_section_alignment (s, bed->s->log_file_align)) |
6de2ae4a L |
96 | return FALSE; |
97 | htab->igotplt = s; | |
98 | } | |
99 | ||
100 | return TRUE; | |
101 | } | |
e03a8ed8 | 102 | |
e03a8ed8 L |
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 | unsigned int plt_entry_size, | |
7b70956d | 111 | unsigned int plt_header_size, |
233cc9c1 L |
112 | unsigned int got_entry_size, |
113 | bfd_boolean avoid_plt) | |
e03a8ed8 L |
114 | { |
115 | asection *plt, *gotplt, *relplt; | |
116 | struct elf_dyn_relocs *p; | |
117 | unsigned int sizeof_reloc; | |
118 | const struct elf_backend_data *bed; | |
119 | struct elf_link_hash_table *htab; | |
233cc9c1 L |
120 | /* If AVOID_PLT is TRUE, don't use PLT if possible. */ |
121 | bfd_boolean use_plt = !avoid_plt || h->plt.refcount > 0; | |
122 | bfd_boolean need_dynreloc = !use_plt || bfd_link_pic (info); | |
123 | ||
124 | /* When a PIC object references a STT_GNU_IFUNC symbol defined | |
125 | in executable or it isn't referenced via PLT, the address of | |
126 | the resolved function may be used. But in non-PIC executable, | |
127 | the address of its .plt slot may be used. Pointer equality may | |
128 | not work correctly. PIE or non-PLT reference should be used if | |
4ec09950 L |
129 | pointer equality is required here. |
130 | ||
131 | If STT_GNU_IFUNC symbol is defined in position-dependent executable, | |
132 | backend should change it to the normal function and set its address | |
133 | to its PLT entry which should be resolved by R_*_IRELATIVE at | |
134 | run-time. All external references should be resolved to its PLT in | |
135 | executable. */ | |
233cc9c1 | 136 | if (!need_dynreloc |
4ec09950 | 137 | && !(bfd_link_pde (info) && h->def_regular) |
e03a8ed8 L |
138 | && (h->dynindx != -1 |
139 | || info->export_dynamic) | |
140 | && h->pointer_equality_needed) | |
141 | { | |
68ffbac6 | 142 | info->callbacks->einfo |
695344c0 | 143 | /* xgettext:c-format */ |
e03a8ed8 | 144 | (_("%F%P: dynamic STT_GNU_IFUNC symbol `%s' with pointer " |
871b3ab2 | 145 | "equality in `%pB' can not be used when making an " |
e03a8ed8 L |
146 | "executable; recompile with -fPIE and relink with -pie\n"), |
147 | h->root.root.string, | |
148 | h->root.u.def.section->owner); | |
149 | bfd_set_error (bfd_error_bad_value); | |
150 | return FALSE; | |
151 | } | |
152 | ||
004fb780 L |
153 | htab = elf_hash_table (info); |
154 | ||
233cc9c1 L |
155 | /* When the symbol is marked with regular reference, if PLT isn't used |
156 | or we are building a PIC object, we must keep dynamic relocation | |
157 | if there is non-GOT reference and use PLT if there is PC-relative | |
158 | reference. */ | |
159 | if (need_dynreloc && h->ref_regular) | |
160 | { | |
161 | bfd_boolean keep = FALSE; | |
162 | for (p = *head; p != NULL; p = p->next) | |
163 | if (p->count) | |
164 | { | |
165 | h->non_got_ref = 1; | |
166 | /* Need dynamic relocations for non-GOT reference. */ | |
167 | keep = TRUE; | |
168 | if (p->pc_count) | |
169 | { | |
170 | /* Must use PLT for PC-relative reference. */ | |
171 | use_plt = TRUE; | |
172 | need_dynreloc = bfd_link_pic (info); | |
173 | break; | |
174 | } | |
175 | } | |
176 | if (keep) | |
177 | goto keep; | |
178 | } | |
1622ff3b | 179 | |
bb1cb422 L |
180 | /* Support garbage collection against STT_GNU_IFUNC symbols. */ |
181 | if (h->plt.refcount <= 0 && h->got.refcount <= 0) | |
182 | { | |
7be86737 L |
183 | h->got = htab->init_got_offset; |
184 | h->plt = htab->init_plt_offset; | |
185 | *head = NULL; | |
186 | return TRUE; | |
bb1cb422 L |
187 | } |
188 | ||
e03a8ed8 | 189 | /* Return and discard space for dynamic relocations against it if |
233cc9c1 | 190 | it is never referenced. */ |
e03a8ed8 L |
191 | if (!h->ref_regular) |
192 | { | |
193 | if (h->plt.refcount > 0 | |
194 | || h->got.refcount > 0) | |
195 | abort (); | |
004fb780 L |
196 | h->got = htab->init_got_offset; |
197 | h->plt = htab->init_plt_offset; | |
e03a8ed8 L |
198 | *head = NULL; |
199 | return TRUE; | |
200 | } | |
201 | ||
dc1e8a47 | 202 | keep: |
e03a8ed8 L |
203 | bed = get_elf_backend_data (info->output_bfd); |
204 | if (bed->rela_plts_and_copies_p) | |
205 | sizeof_reloc = bed->s->sizeof_rela; | |
206 | else | |
207 | sizeof_reloc = bed->s->sizeof_rel; | |
208 | ||
e03a8ed8 L |
209 | /* When building a static executable, use .iplt, .igot.plt and |
210 | .rel[a].iplt sections for STT_GNU_IFUNC symbols. */ | |
211 | if (htab->splt != NULL) | |
212 | { | |
213 | plt = htab->splt; | |
214 | gotplt = htab->sgotplt; | |
215 | relplt = htab->srelplt; | |
216 | ||
233cc9c1 L |
217 | /* If this is the first .plt entry and PLT is used, make room for |
218 | the special first entry. */ | |
219 | if (plt->size == 0 && use_plt) | |
7b70956d | 220 | plt->size += plt_header_size; |
e03a8ed8 L |
221 | } |
222 | else | |
223 | { | |
224 | plt = htab->iplt; | |
225 | gotplt = htab->igotplt; | |
226 | relplt = htab->irelplt; | |
227 | } | |
228 | ||
233cc9c1 L |
229 | if (use_plt) |
230 | { | |
231 | /* Don't update value of STT_GNU_IFUNC symbol to PLT. We need | |
232 | the original value for R_*_IRELATIVE. */ | |
233 | h->plt.offset = plt->size; | |
e03a8ed8 | 234 | |
233cc9c1 L |
235 | /* Make room for this entry in the .plt/.iplt section. */ |
236 | plt->size += plt_entry_size; | |
e03a8ed8 | 237 | |
233cc9c1 L |
238 | /* We also need to make an entry in the .got.plt/.got.iplt section, |
239 | which will be placed in the .got section by the linker script. */ | |
240 | gotplt->size += got_entry_size; | |
241 | } | |
e03a8ed8 L |
242 | |
243 | /* We also need to make an entry in the .rel[a].plt/.rel[a].iplt | |
233cc9c1 L |
244 | section for GOTPLT relocation if PLT is used. */ |
245 | if (use_plt) | |
246 | { | |
247 | relplt->size += sizeof_reloc; | |
248 | relplt->reloc_count++; | |
249 | } | |
e03a8ed8 L |
250 | |
251 | /* We need dynamic relocation for STT_GNU_IFUNC symbol only when | |
233cc9c1 L |
252 | there is a non-GOT reference in a PIC object or PLT isn't used. */ |
253 | if (!need_dynreloc || !h->non_got_ref) | |
e03a8ed8 L |
254 | *head = NULL; |
255 | ||
256 | /* Finally, allocate space. */ | |
7be86737 L |
257 | p = *head; |
258 | if (p != NULL) | |
259 | { | |
260 | bfd_size_type count = 0; | |
261 | do | |
262 | { | |
263 | count += p->count; | |
264 | p = p->next; | |
265 | } | |
266 | while (p != NULL); | |
233cc9c1 | 267 | |
cebd6b8a L |
268 | htab->ifunc_resolvers = count != 0; |
269 | ||
233cc9c1 L |
270 | /* Dynamic relocations are stored in |
271 | 1. .rel[a].ifunc section in PIC object. | |
272 | 2. .rel[a].got section in dynamic executable. | |
273 | 3. .rel[a].iplt section in static executable. */ | |
274 | if (bfd_link_pic (info)) | |
275 | htab->irelifunc->size += count * sizeof_reloc; | |
276 | else if (htab->splt != NULL) | |
277 | htab->srelgot->size += count * sizeof_reloc; | |
278 | else | |
279 | { | |
280 | relplt->size += count * sizeof_reloc; | |
281 | relplt->reloc_count += count; | |
282 | } | |
7be86737 | 283 | } |
e03a8ed8 | 284 | |
7be86737 | 285 | /* For STT_GNU_IFUNC symbol, .got.plt has the real function address |
e03a8ed8 L |
286 | and .got has the PLT entry adddress. We will load the GOT entry |
287 | with the PLT entry in finish_dynamic_symbol if it is used. For | |
233cc9c1 L |
288 | branch, it uses .got.plt. For symbol value, if PLT is used, |
289 | 1. Use .got.plt in a PIC object if it is forced local or not | |
e03a8ed8 | 290 | dynamic. |
233cc9c1 | 291 | 2. Use .got.plt in a non-PIC object if pointer equality isn't |
e03a8ed8 L |
292 | needed. |
293 | 3. Use .got.plt in PIE. | |
294 | 4. Use .got.plt if .got isn't used. | |
295 | 5. Otherwise use .got so that it can be shared among different | |
296 | objects at run-time. | |
233cc9c1 L |
297 | If PLT isn't used, always use .got for symbol value. |
298 | We only need to relocate .got entry in PIC object or in dynamic | |
299 | executable without PLT. */ | |
300 | if (use_plt | |
301 | && (h->got.refcount <= 0 | |
302 | || (bfd_link_pic (info) | |
303 | && (h->dynindx == -1 | |
304 | || h->forced_local)) | |
305 | || (!bfd_link_pic (info) | |
306 | && !h->pointer_equality_needed) | |
307 | || bfd_link_pie (info) | |
308 | || htab->sgot == NULL)) | |
e03a8ed8 L |
309 | { |
310 | /* Use .got.plt. */ | |
311 | h->got.offset = (bfd_vma) -1; | |
312 | } | |
313 | else | |
314 | { | |
233cc9c1 L |
315 | if (!use_plt) |
316 | { | |
317 | /* PLT isn't used. */ | |
318 | h->plt.offset = (bfd_vma) -1; | |
319 | } | |
320 | if (h->got.refcount <= 0) | |
321 | { | |
322 | /* GOT isn't need when there are only relocations for static | |
323 | pointers. */ | |
324 | h->got.offset = (bfd_vma) -1; | |
325 | } | |
326 | else | |
327 | { | |
328 | h->got.offset = htab->sgot->size; | |
329 | htab->sgot->size += got_entry_size; | |
330 | /* Need to relocate the GOT entry in a PIC object or PLT isn't | |
331 | used. Otherwise, the GOT entry will be filled with the PLT | |
332 | entry and dynamic GOT relocation isn't needed. */ | |
333 | if (need_dynreloc) | |
334 | { | |
335 | /* For non-static executable, dynamic GOT relocation is in | |
336 | .rel[a].got section, but for static executable, it is | |
337 | in .rel[a].iplt section. */ | |
338 | if (htab->splt != NULL) | |
339 | htab->srelgot->size += sizeof_reloc; | |
340 | else | |
341 | { | |
342 | relplt->size += sizeof_reloc; | |
343 | relplt->reloc_count++; | |
344 | } | |
345 | } | |
346 | } | |
e03a8ed8 L |
347 | } |
348 | ||
349 | return TRUE; | |
350 | } |