Go to most recent revision | Details | Last modification | View Log | RSS feed
Rev | Author | Line No. | Line |
---|---|---|---|
5197 | serge | 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 | }=>=>=> |