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 /* Allocate space in .plt, .got and associated reloc sections for
108 dynamic relocs against a STT_GNU_IFUNC symbol definition. */
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
)
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
;
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. */
131 || info
->export_dynamic
)
132 && h
->pointer_equality_needed
)
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"),
139 h
->root
.u
.def
.section
->owner
);
140 bfd_set_error (bfd_error_bad_value
);
144 htab
= elf_hash_table (info
);
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
)
157 /* Support garbage collection against STT_GNU_IFUNC symbols. */
158 if (h
->plt
.refcount
<= 0 && h
->got
.refcount
<= 0)
160 h
->got
= htab
->init_got_offset
;
161 h
->plt
= htab
->init_plt_offset
;
166 /* Return and discard space for dynamic relocations against it if
167 it is never referenced in a non-shared object. */
170 if (h
->plt
.refcount
> 0
171 || h
->got
.refcount
> 0)
173 h
->got
= htab
->init_got_offset
;
174 h
->plt
= htab
->init_plt_offset
;
180 bed
= get_elf_backend_data (info
->output_bfd
);
181 if (bed
->rela_plts_and_copies_p
)
182 sizeof_reloc
= bed
->s
->sizeof_rela
;
184 sizeof_reloc
= bed
->s
->sizeof_rel
;
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
)
191 gotplt
= htab
->sgotplt
;
192 relplt
= htab
->srelplt
;
194 /* If this is the first .plt entry, make room for the special
197 plt
->size
+= plt_header_size
;
202 gotplt
= htab
->igotplt
;
203 relplt
= htab
->irelplt
;
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
;
210 /* Make room for this entry in the .plt/.iplt section. */
211 plt
->size
+= plt_entry_size
;
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
;
217 /* We also need to make an entry in the .rel[a].plt/.rel[a].iplt
219 relplt
->size
+= sizeof_reloc
;
220 relplt
->reloc_count
++;
222 /* We need dynamic relocation for STT_GNU_IFUNC symbol only when
223 there is a non-GOT reference in a shared object. */
228 /* Finally, allocate space. */
232 bfd_size_type count
= 0;
239 htab
->irelifunc
->size
+= count
* sizeof_reloc
;
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
248 2. Use .got.plt in a non-shared object if pointer equality isn't
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
254 We only need to relocate .got entry in shared object. */
255 if (h
->got
.refcount
<= 0
260 && !h
->pointer_equality_needed
)
261 || (info
->executable
&& info
->shared
)
262 || htab
->sgot
== NULL
)
265 h
->got
.offset
= (bfd_vma
) -1;
269 h
->got
.offset
= htab
->sgot
->size
;
270 htab
->sgot
->size
+= got_entry_size
;
272 htab
->srelgot
->size
+= sizeof_reloc
;
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