1 /* ELF STT_GNU_IFUNC support.
3 Free Software Foundation, Inc.
5 This file is part of BFD, the Binary File Descriptor library.
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.
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.
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. */
28 #include "safe-ctype.h"
29 #include "libiberty.h"
32 /* Create sections needed by STT_GNU_IFUNC symbol. */
35 _bfd_elf_create_ifunc_sections (bfd
*abfd
, struct bfd_link_info
*info
)
37 flagword flags
, pltflags
;
39 const struct elf_backend_data
*bed
= get_elf_backend_data (abfd
);
40 struct elf_link_hash_table
*htab
= elf_hash_table (info
);
42 if (htab
->irelifunc
!= NULL
|| htab
->iplt
!= NULL
)
45 flags
= bed
->dynamic_sec_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
);
53 pltflags
|= SEC_ALLOC
| SEC_CODE
| SEC_LOAD
;
54 if (bed
->plt_readonly
)
55 pltflags
|= SEC_READONLY
;
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");
63 s
= bfd_make_section_with_flags (abfd
, rel_sec
,
64 flags
| SEC_READONLY
);
66 || ! bfd_set_section_alignment (abfd
, s
,
67 bed
->s
->log_file_align
))
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
);
77 || ! bfd_set_section_alignment (abfd
, s
, bed
->plt_alignment
))
81 s
= bfd_make_section_with_flags (abfd
,
82 (bed
->rela_plts_and_copies_p
83 ? ".rela.iplt" : ".rel.iplt"),
84 flags
| SEC_READONLY
);
86 || ! bfd_set_section_alignment (abfd
, s
,
87 bed
->s
->log_file_align
))
91 /* We don't need the .igot section if we have the .igot.plt
93 if (bed
->want_got_plt
)
94 s
= bfd_make_section_with_flags (abfd
, ".igot.plt", flags
);
96 s
= bfd_make_section_with_flags (abfd
, ".igot", flags
);
98 || !bfd_set_section_alignment (abfd
, s
,
99 bed
->s
->log_file_align
))
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. */
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
)
115 struct elf_dyn_relocs
*p
;
116 struct elf_link_hash_table
*htab
= elf_hash_table (info
);
120 const struct elf_backend_data
*bed
= get_elf_backend_data (abfd
);
122 if (htab
->dynobj
== NULL
)
125 sreloc
= _bfd_elf_make_dynamic_reloc_section (sec
, htab
->dynobj
,
126 bed
->s
->log_file_align
,
128 bed
->rela_plts_and_copies_p
);
134 if (p
== NULL
|| p
->sec
!= sec
)
136 bfd_size_type amt
= sizeof *p
;
138 p
= ((struct elf_dyn_relocs
*) bfd_alloc (htab
->dynobj
, amt
));
152 /* Allocate space in .plt, .got and associated reloc sections for
153 dynamic relocs against a STT_GNU_IFUNC symbol definition. */
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
)
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
;
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. */
175 || info
->export_dynamic
)
176 && h
->pointer_equality_needed
)
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"),
183 h
->root
.u
.def
.section
->owner
);
184 bfd_set_error (bfd_error_bad_value
);
188 htab
= elf_hash_table (info
);
190 /* Support garbage collection against STT_GNU_IFUNC symbols. */
191 if (h
->plt
.refcount
<= 0 && h
->got
.refcount
<= 0)
193 h
->got
= htab
->init_got_offset
;
194 h
->plt
= htab
->init_plt_offset
;
199 /* Return and discard space for dynamic relocations against it if
200 it is never referenced in a non-shared object. */
203 if (h
->plt
.refcount
> 0
204 || h
->got
.refcount
> 0)
206 h
->got
= htab
->init_got_offset
;
207 h
->plt
= htab
->init_plt_offset
;
212 bed
= get_elf_backend_data (info
->output_bfd
);
213 if (bed
->rela_plts_and_copies_p
)
214 sizeof_reloc
= bed
->s
->sizeof_rela
;
216 sizeof_reloc
= bed
->s
->sizeof_rel
;
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
)
223 gotplt
= htab
->sgotplt
;
224 relplt
= htab
->srelplt
;
226 /* If this is the first .plt entry, make room for the special
229 plt
->size
+= plt_entry_size
;
234 gotplt
= htab
->igotplt
;
235 relplt
= htab
->irelplt
;
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
;
242 /* Make room for this entry in the .plt/.iplt section. */
243 plt
->size
+= plt_entry_size
;
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
;
249 /* We also need to make an entry in the .rel[a].plt/.rel[a].iplt
251 relplt
->size
+= sizeof_reloc
;
252 relplt
->reloc_count
++;
254 /* We need dynamic relocation for STT_GNU_IFUNC symbol only when
255 there is a non-GOT reference in a shared object. */
260 /* Finally, allocate space. */
261 for (p
= *head
; p
!= NULL
; p
= p
->next
)
262 htab
->irelifunc
->size
+= p
->count
* sizeof_reloc
;
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
270 2. Use .got.plt in a non-shared object if pointer equality isn't
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
276 We only need to relocate .got entry in shared object. */
281 && !h
->pointer_equality_needed
)
282 || (info
->executable
&& info
->shared
)
283 || htab
->sgot
== NULL
)
286 h
->got
.offset
= (bfd_vma
) -1;
290 h
->got
.offset
= htab
->sgot
->size
;
291 htab
->sgot
->size
+= got_entry_size
;
293 htab
->srelgot
->size
+= sizeof_reloc
;
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