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- /* ELF STT_GNU_IFUNC support.
- Copyright (C) 2009-2022 Free Software Foundation, Inc.
- This file is part of BFD, the Binary File Descriptor library.
- This program is free software; you can redistribute it and/or modify
- it under the terms of the GNU General Public License as published by
- the Free Software Foundation; either version 3 of the License, or
- (at your option) any later version.
- This program is distributed in the hope that it will be useful,
- but WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- GNU General Public License for more details.
- You should have received a copy of the GNU General Public License
- along with this program; if not, write to the Free Software
- Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
- MA 02110-1301, USA. */
- #include "sysdep.h"
- #include "bfd.h"
- #include "bfdlink.h"
- #include "libbfd.h"
- #define ARCH_SIZE 0
- #include "elf-bfd.h"
- #include "safe-ctype.h"
- #include "libiberty.h"
- #include "objalloc.h"
- /* Create sections needed by STT_GNU_IFUNC symbol. */
- bool
- _bfd_elf_create_ifunc_sections (bfd *abfd, struct bfd_link_info *info)
- {
- flagword flags, pltflags;
- asection *s;
- const struct elf_backend_data *bed = get_elf_backend_data (abfd);
- struct elf_link_hash_table *htab = elf_hash_table (info);
- if (htab->irelifunc != NULL || htab->iplt != NULL)
- return true;
- flags = bed->dynamic_sec_flags;
- pltflags = flags;
- if (bed->plt_not_loaded)
- /* We do not clear SEC_ALLOC here because we still want the OS to
- allocate space for the section; it's just that there's nothing
- to read in from the object file. */
- pltflags &= ~ (SEC_CODE | SEC_LOAD | SEC_HAS_CONTENTS);
- else
- pltflags |= SEC_ALLOC | SEC_CODE | SEC_LOAD;
- if (bed->plt_readonly)
- pltflags |= SEC_READONLY;
- if (bfd_link_pic (info))
- {
- /* We need to create .rel[a].ifunc for PIC objects. */
- const char *rel_sec = (bed->rela_plts_and_copies_p
- ? ".rela.ifunc" : ".rel.ifunc");
- s = bfd_make_section_with_flags (abfd, rel_sec,
- flags | SEC_READONLY);
- if (s == NULL
- || !bfd_set_section_alignment (s, bed->s->log_file_align))
- return false;
- htab->irelifunc = s;
- }
- else
- {
- /* We need to create .iplt, .rel[a].iplt, .igot and .igot.plt
- for static executables. */
- s = bfd_make_section_with_flags (abfd, ".iplt", pltflags);
- if (s == NULL
- || !bfd_set_section_alignment (s, bed->plt_alignment))
- return false;
- htab->iplt = s;
- s = bfd_make_section_with_flags (abfd,
- (bed->rela_plts_and_copies_p
- ? ".rela.iplt" : ".rel.iplt"),
- flags | SEC_READONLY);
- if (s == NULL
- || !bfd_set_section_alignment (s, bed->s->log_file_align))
- return false;
- htab->irelplt = s;
- /* We don't need the .igot section if we have the .igot.plt
- section. */
- if (bed->want_got_plt)
- s = bfd_make_section_with_flags (abfd, ".igot.plt", flags);
- else
- s = bfd_make_section_with_flags (abfd, ".igot", flags);
- if (s == NULL
- || !bfd_set_section_alignment (s, bed->s->log_file_align))
- return false;
- htab->igotplt = s;
- }
- return true;
- }
- /* Allocate space in .plt, .got and associated reloc sections for
- dynamic relocs against a STT_GNU_IFUNC symbol definition. */
- bool
- _bfd_elf_allocate_ifunc_dyn_relocs (struct bfd_link_info *info,
- struct elf_link_hash_entry *h,
- struct elf_dyn_relocs **head,
- unsigned int plt_entry_size,
- unsigned int plt_header_size,
- unsigned int got_entry_size,
- bool avoid_plt)
- {
- asection *plt, *gotplt, *relplt;
- struct elf_dyn_relocs *p;
- unsigned int sizeof_reloc;
- const struct elf_backend_data *bed;
- struct elf_link_hash_table *htab;
- /* If AVOID_PLT is TRUE, don't use PLT if possible. */
- bool use_plt = !avoid_plt || h->plt.refcount > 0;
- bool need_dynreloc = !use_plt || bfd_link_pic (info);
- /* When a PIC object references a STT_GNU_IFUNC symbol defined
- in executable or it isn't referenced via PLT, the address of
- the resolved function may be used. But in non-PIC executable,
- the address of its .plt slot may be used. Pointer equality may
- not work correctly. PIE or non-PLT reference should be used if
- pointer equality is required here.
- If STT_GNU_IFUNC symbol is defined in position-dependent executable,
- backend should change it to the normal function and set its address
- to its PLT entry which should be resolved by R_*_IRELATIVE at
- run-time. All external references should be resolved to its PLT in
- executable. */
- if (!need_dynreloc
- && !(bfd_link_pde (info) && h->def_regular)
- && (h->dynindx != -1
- || info->export_dynamic)
- && h->pointer_equality_needed)
- {
- info->callbacks->einfo
- /* xgettext:c-format */
- (_("%F%P: dynamic STT_GNU_IFUNC symbol `%s' with pointer "
- "equality in `%pB' can not be used when making an "
- "executable; recompile with -fPIE and relink with -pie\n"),
- h->root.root.string,
- h->root.u.def.section->owner);
- bfd_set_error (bfd_error_bad_value);
- return false;
- }
- htab = elf_hash_table (info);
- /* When the symbol is marked with regular reference, if PLT isn't used
- or we are building a PIC object, we must keep dynamic relocation
- if there is non-GOT reference and use PLT if there is PC-relative
- reference. */
- if (need_dynreloc && h->ref_regular)
- {
- bool keep = false;
- for (p = *head; p != NULL; p = p->next)
- if (p->count)
- {
- h->non_got_ref = 1;
- /* Need dynamic relocations for non-GOT reference. */
- keep = true;
- if (p->pc_count)
- {
- /* Must use PLT for PC-relative reference. */
- use_plt = true;
- need_dynreloc = bfd_link_pic (info);
- break;
- }
- }
- if (keep)
- goto keep;
- }
- /* Support garbage collection against STT_GNU_IFUNC symbols. */
- if (h->plt.refcount <= 0 && h->got.refcount <= 0)
- {
- h->got = htab->init_got_offset;
- h->plt = htab->init_plt_offset;
- *head = NULL;
- return true;
- }
- /* Return and discard space for dynamic relocations against it if
- it is never referenced. */
- if (!h->ref_regular)
- {
- if (h->plt.refcount > 0
- || h->got.refcount > 0)
- abort ();
- h->got = htab->init_got_offset;
- h->plt = htab->init_plt_offset;
- *head = NULL;
- return true;
- }
- keep:
- bed = get_elf_backend_data (info->output_bfd);
- if (bed->rela_plts_and_copies_p)
- sizeof_reloc = bed->s->sizeof_rela;
- else
- sizeof_reloc = bed->s->sizeof_rel;
- /* When building a static executable, use .iplt, .igot.plt and
- .rel[a].iplt sections for STT_GNU_IFUNC symbols. */
- if (htab->splt != NULL)
- {
- plt = htab->splt;
- gotplt = htab->sgotplt;
- relplt = htab->srelplt;
- /* If this is the first .plt entry and PLT is used, make room for
- the special first entry. */
- if (plt->size == 0 && use_plt)
- plt->size += plt_header_size;
- }
- else
- {
- plt = htab->iplt;
- gotplt = htab->igotplt;
- relplt = htab->irelplt;
- }
- if (use_plt)
- {
- /* Don't update value of STT_GNU_IFUNC symbol to PLT. We need
- the original value for R_*_IRELATIVE. */
- h->plt.offset = plt->size;
- /* Make room for this entry in the .plt/.iplt section. */
- plt->size += plt_entry_size;
- /* We also need to make an entry in the .got.plt/.got.iplt section,
- which will be placed in the .got section by the linker script. */
- gotplt->size += got_entry_size;
- }
- /* We also need to make an entry in the .rel[a].plt/.rel[a].iplt
- section for GOTPLT relocation if PLT is used. */
- if (use_plt)
- {
- relplt->size += sizeof_reloc;
- relplt->reloc_count++;
- }
- /* We need dynamic relocation for STT_GNU_IFUNC symbol only when
- there is a non-GOT reference in a PIC object or PLT isn't used. */
- if (!need_dynreloc || !h->non_got_ref)
- *head = NULL;
- /* Finally, allocate space. */
- p = *head;
- if (p != NULL)
- {
- bfd_size_type count = 0;
- do
- {
- count += p->count;
- p = p->next;
- }
- while (p != NULL);
- htab->ifunc_resolvers = count != 0;
- /* Dynamic relocations are stored in
- 1. .rel[a].ifunc section in PIC object.
- 2. .rel[a].got section in dynamic executable.
- 3. .rel[a].iplt section in static executable. */
- if (bfd_link_pic (info))
- htab->irelifunc->size += count * sizeof_reloc;
- else if (htab->splt != NULL)
- htab->srelgot->size += count * sizeof_reloc;
- else
- {
- relplt->size += count * sizeof_reloc;
- relplt->reloc_count += count;
- }
- }
- /* For STT_GNU_IFUNC symbol, .got.plt has the real function address
- and .got has the PLT entry adddress. We will load the GOT entry
- with the PLT entry in finish_dynamic_symbol if it is used. For
- branch, it uses .got.plt. For symbol value, if PLT is used,
- 1. Use .got.plt in a PIC object if it is forced local or not
- dynamic.
- 2. Use .got.plt in a non-PIC object if pointer equality isn't
- needed.
- 3. Use .got.plt in PIE.
- 4. Use .got.plt if .got isn't used.
- 5. Otherwise use .got so that it can be shared among different
- objects at run-time.
- If PLT isn't used, always use .got for symbol value.
- We only need to relocate .got entry in PIC object or in dynamic
- executable without PLT. */
- if (use_plt
- && (h->got.refcount <= 0
- || (bfd_link_pic (info)
- && (h->dynindx == -1
- || h->forced_local))
- || (!bfd_link_pic (info)
- && !h->pointer_equality_needed)
- || bfd_link_pie (info)
- || htab->sgot == NULL))
- {
- /* Use .got.plt. */
- h->got.offset = (bfd_vma) -1;
- }
- else
- {
- if (!use_plt)
- {
- /* PLT isn't used. */
- h->plt.offset = (bfd_vma) -1;
- }
- if (h->got.refcount <= 0)
- {
- /* GOT isn't need when there are only relocations for static
- pointers. */
- h->got.offset = (bfd_vma) -1;
- }
- else
- {
- h->got.offset = htab->sgot->size;
- htab->sgot->size += got_entry_size;
- /* Need to relocate the GOT entry in a PIC object or PLT isn't
- used. Otherwise, the GOT entry will be filled with the PLT
- entry and dynamic GOT relocation isn't needed. */
- if (need_dynreloc)
- {
- /* For non-static executable, dynamic GOT relocation is in
- .rel[a].got section, but for static executable, it is
- in .rel[a].iplt section. */
- if (htab->splt != NULL)
- htab->srelgot->size += sizeof_reloc;
- else
- {
- relplt->size += sizeof_reloc;
- relplt->reloc_count++;
- }
- }
- }
- }
- return true;
- }
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