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/* ldctor.c -- constructor support routines
Copyright (C) 1991-2023 Free Software Foundation, Inc.
By Steve Chamberlain <>
This file is part of the GNU Binutils.
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
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 "libiberty.h"
#include "bfd.h"
#include "bfdlink.h"
#include "safe-ctype.h"
#include "ctf-api.h"
#include "ld.h"
#include "ldexp.h"
#include "ldlang.h"
#include "ldmisc.h"
#include <ldgram.h>
#include "ldmain.h"
#include "ldctor.h"
/* The list of statements needed to handle constructors. These are
invoked by the command CONSTRUCTORS in the linker script. */
lang_statement_list_type constructor_list;
/* Whether the constructors should be sorted. Note that this is
global for the entire link; we assume that there is only a single
CONSTRUCTORS command in the linker script. */
bool constructors_sorted;
/* The sets we have seen. */
struct set_info *sets;
/* Add an entry to a set. H is the entry in the linker hash table.
RELOC is the relocation to use for an entry in the set. SECTION
and VALUE are the value to add. This is called during the first
phase of the link, when we are still gathering symbols together.
We just record the information now. The ldctor_build_sets
function will construct the sets. */
ldctor_add_set_entry (struct bfd_link_hash_entry *h,
bfd_reloc_code_real_type reloc,
const char *name,
asection *section,
bfd_vma value)
struct set_info *p;
struct set_element *e;
struct set_element **epp;
for (p = sets; p != NULL; p = p->next)
if (p->h == h)
if (p == NULL)
p = (struct set_info *) xmalloc (sizeof (struct set_info));
p->next = sets;
sets = p;
p->h = h;
p->reloc = reloc;
p->count = 0;
p->elements = NULL;
if (p->reloc != reloc)
einfo (_("%X%P: different relocs used in set %s\n"),
/* Don't permit a set to be constructed from different object
file formats. The same reloc may have different results. We
actually could sometimes handle this, but the case is
unlikely to ever arise. Sometimes constructor symbols are in
unusual sections, such as the absolute section--this appears
to be the case in Linux a.out--and in such cases we just
assume everything is OK. */
if (p->elements != NULL
&& section->owner != NULL
&& p->elements->section->owner != NULL
&& strcmp (bfd_get_target (section->owner),
bfd_get_target (p->elements->section->owner)) != 0)
einfo (_("%X%P: different object file formats composing set %s\n"),
e = (struct set_element *) xmalloc (sizeof (struct set_element));
e-> = NULL;
e->name = name;
e->section = section;
e->value = value;
for (epp = &p->elements; *epp != NULL; epp = &(*epp)->
*epp = e;
/* Get the priority of a g++ global constructor or destructor from the
symbol name. */
static int
ctor_prio (const char *name)
/* The name will look something like _GLOBAL_$I$65535$test02__Fv.
There might be extra leading underscores, and the $ characters
might be something else. The I might be a D. */
while (*name == '_')
if (!startswith (name, "GLOBAL_"))
return -1;
name += sizeof "GLOBAL_" - 1;
if (name[0] != name[2])
return -1;
if (name[1] != 'I' && name[1] != 'D')
return -1;
if (!ISDIGIT (name[3]))
return -1;
return atoi (name + 3);
/* This function is used to sort constructor elements by priority. It
is called via qsort. */
static int
ctor_cmp (const void *p1, const void *p2)
const struct set_element *pe1 = *(const struct set_element **) p1;
const struct set_element *pe2 = *(const struct set_element **) p2;
const char *n1;
const char *n2;
int prio1;
int prio2;
n1 = pe1->name;
if (n1 == NULL)
n1 = "";
n2 = pe2->name;
if (n2 == NULL)
n2 = "";
/* We need to sort in reverse order by priority. When two
constructors have the same priority, we should maintain their
current relative position. */
prio1 = ctor_prio (n1);
prio2 = ctor_prio (n2);
/* We sort in reverse order because that is what g++ expects. */
if (prio1 < prio2)
return 1;
if (prio1 > prio2)
return -1;
/* Force a stable sort. */
if (pe1->u.idx < pe2->u.idx)
return -1;
if (pe1->u.idx > pe2->u.idx)
return 1;
return 0;
/* This function is called after the first phase of the link and
before the second phase. At this point all set information has
been gathered. We now put the statements to build the sets
themselves into constructor_list. */
ldctor_build_sets (void)
static bool called;
bool header_printed;
struct set_info *p;
/* The emulation code may call us directly, but we only want to do
this once. */
if (called)
called = true;
if (constructors_sorted)
for (p = sets; p != NULL; p = p->next)
int c, i;
struct set_element *e, *enext;
struct set_element **array;
if (p->elements == NULL)
c = 0;
for (e = p->elements; e != NULL; e = e->
array = (struct set_element **) xmalloc (c * sizeof *array);
i = 0;
for (e = p->elements; e != NULL; e = enext)
array[i] = e;
enext = e->;
e->u.idx = i;
qsort (array, c, sizeof *array, ctor_cmp);
e = array[0];
p->elements = e;
for (i = 0; i < c - 1; i++)
array[i]-> = array[i + 1];
array[i]-> = NULL;
free (array);
lang_list_init (&constructor_list);
push_stat_ptr (&constructor_list);
header_printed = false;
for (p = sets; p != NULL; p = p->next)
struct set_element *e;
reloc_howto_type *howto;
int reloc_size, size;
/* If the symbol is defined, we may have been invoked from
collect, and the sets may already have been built, so we do
not do anything. */
if (p->h->type == bfd_link_hash_defined
|| p->h->type == bfd_link_hash_defweak)
/* For each set we build:
.long number_of_elements
.long element0
.long elementN
.long 0
except that we use the right size instead of .long. When
generating relocatable output, we generate relocs instead of
addresses. */
howto = bfd_reloc_type_lookup (link_info.output_bfd, p->reloc);
if (howto == NULL)
if (bfd_link_relocatable (&link_info))
einfo (_("%X%P: %s does not support reloc %s for set %s\n"),
bfd_get_target (link_info.output_bfd),
bfd_get_reloc_code_name (p->reloc),
/* If this is not a relocatable link, all we need is the
size, which we can get from the input BFD. */
if (p->elements->section->owner != NULL)
howto = bfd_reloc_type_lookup (p->elements->section->owner,
if (howto == NULL)
/* See PR 20911 for a reproducer. */
if (p->elements->section->owner == NULL)
einfo (_("%X%P: special section %s does not support reloc %s for set %s\n"),
bfd_section_name (p->elements->section),
bfd_get_reloc_code_name (p->reloc),
einfo (_("%X%P: %s does not support reloc %s for set %s\n"),
bfd_get_target (p->elements->section->owner),
bfd_get_reloc_code_name (p->reloc),
reloc_size = bfd_get_reloc_size (howto);
switch (reloc_size)
case 1: size = BYTE; break;
case 2: size = SHORT; break;
case 4: size = LONG; break;
case 8:
if (howto->complain_on_overflow == complain_overflow_signed)
size = SQUAD;
size = QUAD;
einfo (_("%X%P: unsupported size %d for set %s\n"),
bfd_get_reloc_size (howto), p->h->root.string);
size = LONG;
lang_add_assignment (exp_assign (".",
exp_unop (ALIGN_K,
exp_intop (reloc_size)),
lang_add_assignment (exp_assign (p->h->root.string,
exp_nameop (NAME, "."),
lang_add_data (size, exp_intop (p->count));
for (e = p->elements; e != NULL; e = e->
if (config.map_file != NULL)
int len;
if (!header_printed)
minfo (_("\nSet Symbol\n\n"));
header_printed = true;
minfo ("%s", p->h->root.string);
len = strlen (p->h->root.string);
if (len >= 19)
print_nl ();
len = 0;
print_spaces (20 - len);
if (e->name != NULL)
minfo ("%pT\n", e->name);
minfo ("%G\n", e->section->owner, e->section, e->value);
/* Need SEC_KEEP for --gc-sections. */
if (!bfd_is_abs_section (e->section))
e->section->flags |= SEC_KEEP;
if (bfd_link_relocatable (&link_info))
lang_add_reloc (p->reloc, howto, e->section, e->name,
exp_intop (e->value));
lang_add_data (size, exp_relop (e->section, e->value));
lang_add_data (size, exp_intop (0));
pop_stat_ptr ();