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binutils-gdb/bfd/elf-ifunc.c

351 lines
10 KiB
C

/* ELF STT_GNU_IFUNC support.
Copyright (C) 2009-2021 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. */
bfd_boolean
_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. */
bfd_boolean
_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,
bfd_boolean 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. */
bfd_boolean use_plt = !avoid_plt || h->plt.refcount > 0;
bfd_boolean 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)
{
bfd_boolean 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;
}