glibc/elf/dl-init.c

/* Run initializers for newly loaded objects.
   Copyright (C) 1995-2023 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#include <assert.h>
#include <stddef.h>
#include <ldsodefs.h>
#include <elf-initfini.h>

struct link_map *_dl_init_called_list;

static void
call_init (struct link_map *l, int argc, char **argv, char **env)
{
  /* Do not run constructors for proxy objects.  */
  if (l != l->l_real)
    return;

  /* If the object has not been relocated, this is a bug.  The
     function pointers are invalid in this case.  (Executables do not
     need relocation.)  */
  assert (l->l_relocated || l->l_type == lt_executable);

  if (l->l_init_called)
    /* This object is all done.  */
    return;

  /* Avoid handling this constructor again in case we have a circular
     dependency.  */
  l->l_init_called = 1;

  /* Help an already-running dlclose: The just-loaded object must not
     be removed during the current pass.  (No effect if no dlclose in
     progress.)  */
  l->l_map_used = 1;

  /* Record execution before starting any initializers.  This way, if
     the initializers themselves call dlopen, their ELF destructors
     will eventually be run before this object is destructed, matching
     that their ELF constructors have run before this object was
     constructed.  _dl_fini uses this list for audit callbacks, so
     register objects on the list even if they do not have a
     constructor.  */
  l->l_init_called_next = _dl_init_called_list;
  _dl_init_called_list = l;

  /* Check for object which constructors we do not run here.  */
  if (__builtin_expect (l->l_name[0], 'a') == '\0'
      && l->l_type == lt_executable)
    return;

  /* Print a debug message if wanted.  */
  if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_IMPCALLS))
    _dl_debug_printf ("\ncalling init: %s\n\n",
		      DSO_FILENAME (l->l_name));

  /* Now run the local constructors.  There are two forms of them:
     - the one named by DT_INIT
     - the others in the DT_INIT_ARRAY.
  */
  if (ELF_INITFINI && l->l_info[DT_INIT] != NULL)
    DL_CALL_DT_INIT(l, l->l_addr + l->l_info[DT_INIT]->d_un.d_ptr, argc, argv, env);

  /* Next see whether there is an array with initialization functions.  */
  ElfW(Dyn) *init_array = l->l_info[DT_INIT_ARRAY];
  if (init_array != NULL)
    {
      unsigned int j;
      unsigned int jm;
      ElfW(Addr) *addrs;

      jm = l->l_info[DT_INIT_ARRAYSZ]->d_un.d_val / sizeof (ElfW(Addr));

      addrs = (ElfW(Addr) *) (init_array->d_un.d_ptr + l->l_addr);
      for (j = 0; j < jm; ++j)
	((dl_init_t) addrs[j]) (argc, argv, env);
    }
}


void
_dl_init (struct link_map *main_map, int argc, char **argv, char **env)
{
  ElfW(Dyn) *preinit_array = main_map->l_info[DT_PREINIT_ARRAY];
  ElfW(Dyn) *preinit_array_size = main_map->l_info[DT_PREINIT_ARRAYSZ];
  unsigned int i;

  if (__glibc_unlikely (GL(dl_initfirst) != NULL))
    {
      call_init (GL(dl_initfirst), argc, argv, env);
      GL(dl_initfirst) = NULL;
    }

  /* Don't do anything if there is no preinit array.  */
  if (__builtin_expect (preinit_array != NULL, 0)
      && preinit_array_size != NULL
      && (i = preinit_array_size->d_un.d_val / sizeof (ElfW(Addr))) > 0)
    {
      ElfW(Addr) *addrs;
      unsigned int cnt;

      if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_IMPCALLS))
	_dl_debug_printf ("\ncalling preinit: %s\n\n",
			  DSO_FILENAME (main_map->l_name));

      addrs = (ElfW(Addr) *) (preinit_array->d_un.d_ptr + main_map->l_addr);
      for (cnt = 0; cnt < i; ++cnt)
	((dl_init_t) addrs[cnt]) (argc, argv, env);
    }

  /* Stupid users forced the ELF specification to be changed.  It now
     says that the dynamic loader is responsible for determining the
     order in which the constructors have to run.  The constructors
     for all dependencies of an object must run before the constructor
     for the object itself.  Circular dependencies are left unspecified.

     This is highly questionable since it puts the burden on the dynamic
     loader which has to find the dependencies at runtime instead of
     letting the user do it right.  Stupidity rules!  */

  i = main_map->l_searchlist.r_nlist;
  while (i-- > 0)
    call_init (main_map->l_initfini[i], argc, argv, env);

#ifndef HAVE_INLINED_SYSCALLS
  /* Finished starting up.  */
  _dl_starting_up = 0;
#endif
}