/* ELF STT_GNU_IFUNC support.
- Copyright 2009
- Free Software Foundation, Inc.
+ Copyright (C) 2009-2016 Free Software Foundation, Inc.
This file is part of BFD, the Binary File Descriptor library.
if (bed->plt_readonly)
pltflags |= SEC_READONLY;
- if (info->shared)
+ if (bfd_link_pic (info))
{
- /* We need to create .rel[a].ifunc for shared objects. */
+ /* We need to create .rel[a].ifunc for PIC objects. */
const char *rel_sec = (bed->rela_plts_and_copies_p
? ".rela.ifunc" : ".rel.ifunc");
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,
+ bfd_boolean *readonly_dynrelocs_against_ifunc_p,
+ 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;
+ bfd_boolean readonly_dynrelocs_against_ifunc;
+ /* 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 (!need_dynreloc
+ && (h->dynindx != -1
+ || info->export_dynamic)
+ && h->pointer_equality_needed)
+ {
+ info->callbacks->einfo
+ (_("%F%P: dynamic STT_GNU_IFUNC symbol `%s' with pointer "
+ "equality in `%B' 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;
+
+ readonly_dynrelocs_against_ifunc = FALSE;
+
+ /* Finally, allocate space. */
+ p = *head;
+ if (p != NULL)
+ {
+ bfd_size_type count = 0;
+ do
+ {
+ if (!readonly_dynrelocs_against_ifunc)
+ {
+ asection *s = p->sec->output_section;
+ if (s != NULL && (s->flags & SEC_READONLY) != 0)
+ readonly_dynrelocs_against_ifunc = TRUE;
+ }
+ count += p->count;
+ p = p->next;
+ }
+ while (p != NULL);
+
+ /* 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;
+ }
+ }
+
+ if (readonly_dynrelocs_against_ifunc_p)
+ *readonly_dynrelocs_against_ifunc_p = readonly_dynrelocs_against_ifunc;
+
+ /* 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;
+}
+
+/* Similar to _bfd_elf_get_synthetic_symtab, optimized for unsorted PLT
+ entries. PLT is the PLT section. PLT_SYM_VAL is a function pointer
+ which returns an array of PLT entry symbol values. */
+
+long
+_bfd_elf_ifunc_get_synthetic_symtab
+ (bfd *abfd, long symcount ATTRIBUTE_UNUSED,
+ asymbol **syms ATTRIBUTE_UNUSED, long dynsymcount, asymbol **dynsyms,
+ asymbol **ret, asection *plt,
+ bfd_vma *(*get_plt_sym_val) (bfd *, asymbol **, asection *, asection *))
+{
+ const struct elf_backend_data *bed = get_elf_backend_data (abfd);
+ asection *relplt;
+ asymbol *s;
+ const char *relplt_name;
+ bfd_boolean (*slurp_relocs) (bfd *, asection *, asymbol **, bfd_boolean);
+ arelent *p;
+ long count, i, n;
+ size_t size;
+ Elf_Internal_Shdr *hdr;
+ char *names;
+ bfd_vma *plt_sym_val;
+
+ *ret = NULL;
+
+ if (plt == NULL)
+ return 0;
+
+ if ((abfd->flags & (DYNAMIC | EXEC_P)) == 0)
+ return 0;
+
+ if (dynsymcount <= 0)
+ return 0;
+
+ relplt_name = bed->relplt_name;
+ if (relplt_name == NULL)
+ relplt_name = bed->rela_plts_and_copies_p ? ".rela.plt" : ".rel.plt";
+ relplt = bfd_get_section_by_name (abfd, relplt_name);
+ if (relplt == NULL)
+ return 0;
+
+ hdr = &elf_section_data (relplt)->this_hdr;
+ if (hdr->sh_link != elf_dynsymtab (abfd)
+ || (hdr->sh_type != SHT_REL && hdr->sh_type != SHT_RELA))
+ return 0;
+
+ slurp_relocs = get_elf_backend_data (abfd)->s->slurp_reloc_table;
+ if (! (*slurp_relocs) (abfd, relplt, dynsyms, TRUE))
+ return -1;
+
+ count = relplt->size / hdr->sh_entsize;
+ size = count * sizeof (asymbol);
+ p = relplt->relocation;
+ for (i = 0; i < count; i++, p += bed->s->int_rels_per_ext_rel)
+ {
+ size += strlen ((*p->sym_ptr_ptr)->name) + sizeof ("@plt");
+ if (p->addend != 0)
+ {
+#ifdef BFD64
+ size += sizeof ("+0x") - 1 + 8 + 8 * (bed->s->elfclass == ELFCLASS64);
+#else
+ size += sizeof ("+0x") - 1 + 8;
+#endif
+ }
+ }
+
+ plt_sym_val = get_plt_sym_val (abfd, dynsyms, plt, relplt);
+ if (plt_sym_val == NULL)
+ return -1;
+
+ s = *ret = (asymbol *) bfd_malloc (size);
+ if (s == NULL)
+ {
+ free (plt_sym_val);
+ return -1;
+ }
+
+ names = (char *) (s + count);
+ p = relplt->relocation;
+ n = 0;
+ for (i = 0; i < count; i++, p += bed->s->int_rels_per_ext_rel)
+ {
+ size_t len;
+ bfd_vma addr;
+
+ addr = plt_sym_val[i];
+ if (addr == (bfd_vma) -1)
+ continue;
+
+ *s = **p->sym_ptr_ptr;
+ /* Undefined syms won't have BSF_LOCAL or BSF_GLOBAL set. Since
+ we are defining a symbol, ensure one of them is set. */
+ if ((s->flags & BSF_LOCAL) == 0)
+ s->flags |= BSF_GLOBAL;
+ s->flags |= BSF_SYNTHETIC;
+ s->section = plt;
+ s->value = addr - plt->vma;
+ s->name = names;
+ s->udata.p = NULL;
+ len = strlen ((*p->sym_ptr_ptr)->name);
+ memcpy (names, (*p->sym_ptr_ptr)->name, len);
+ names += len;
+ if (p->addend != 0)
+ {
+ char buf[30], *a;
+
+ memcpy (names, "+0x", sizeof ("+0x") - 1);
+ names += sizeof ("+0x") - 1;
+ bfd_sprintf_vma (abfd, buf, p->addend);
+ for (a = buf; *a == '0'; ++a)
+ ;
+ len = strlen (a);
+ memcpy (names, a, len);
+ names += len;
+ }
+ memcpy (names, "@plt", sizeof ("@plt"));
+ names += sizeof ("@plt");
+ ++s, ++n;
+ }
+
+ free (plt_sym_val);
+
+ return n;
+}
projects / deliverable / binutils-gdb.git / blobdiff