resolv/res_libc.c

   1 /* Definitions related to res_init linked into libc instead of libresolv.
   2    Copyright (C) 1995-2017 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 /*
  20  * Copyright (c) 1995-1999 by Internet Software Consortium.
  21  *
  22  * Permission to use, copy, modify, and distribute this software for any
  23  * purpose with or without fee is hereby granted, provided that the above
  24  * copyright notice and this permission notice appear in all copies.
  25  *
  26  * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
  27  * ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
  28  * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
  29  * CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
  30  * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
  31  * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
  32  * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
  33  * SOFTWARE.
  34  */
  35
  36 #include <atomic.h>
  37 #include <limits.h>
  38 #include <sys/types.h>
  39 #include <netinet/in.h>
  40 #include <arpa/nameser.h>
  41 #include <resolv.h>
  42 #include <libc-lock.h>
  43 #include <resolv-internal.h>
  44
  45 int
  46 res_init (void)
  47 {
  48   /* These three fields used to be statically initialized.  This made
  49      it hard to use this code in a shared library.  It is necessary,
  50      now that we're doing dynamic initialization here, that we
  51      preserve the old semantics: if an application modifies one of
  52      these three fields of _res before res_init is called,
  53      res_init will not alter them.  Of course, if an application is
  54      setting them to _zero_ before calling res_init, hoping to
  55      override what used to be the static default, we can't detect it
  56      and unexpected results will follow.  Zero for any of these fields
  57      would make no sense, so one can safely assume that the
  58      applications were already getting unexpected results.
  59
  60      _res.options is tricky since some apps were known to diddle the
  61      bits before res_init was first called. We can't replicate that
  62      semantic with dynamic initialization (they may have turned bits
  63      off that are set in RES_DEFAULT).  Our solution is to declare
  64      such applications "broken".  They could fool us by setting
  65      RES_INIT but none do (yet).  */
  66   if (!_res.retrans)
  67     _res.retrans = RES_TIMEOUT;
  68   if (!_res.retry)
  69     _res.retry = RES_DFLRETRY;
  70   if (!(_res.options & RES_INIT))
  71     _res.options = RES_DEFAULT;
  72   else if (_res.nscount > 0)
  73     __res_iclose (&_res, true); /* Close any VC sockets.  */
  74
  75   /* This one used to initialize implicitly to zero, so unless the app
  76      has set it to something in particular, we can randomize it *
  77      now.  */
  78   if (!_res.id)
  79     _res.id = res_randomid ();
  80
  81   return __res_vinit (&_res, 1);
  82 }
  83 \f
  84 /* This needs to be after the use of _res in res_init, above.  */
  85 #undef _res
  86
  87 /* The resolver state for use by single-threaded programs.
  88    This differs from plain `struct __res_state _res;' in that it doesn't
  89    create a common definition, but a plain symbol that resides in .bss,
  90    which can have an alias.  */
  91 struct __res_state _res __attribute__ ((nocommon));
  92
  93 #undef __resp
  94 __thread struct __res_state *__resp = &_res;
  95 extern __thread struct __res_state *__libc_resp
  96   __attribute__ ((alias ("__resp"))) attribute_hidden;
  97
  98 #include <shlib-compat.h>
  99
 100 /* We declare this with compat_symbol so that it's not
 101    visible at link time.  Programs must use the accessor functions.  */
 102 #ifdef SHARED
 103 compat_symbol (libc, _res, _res, GLIBC_2_0);
 104 #endif
 105
 106 #if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_2)
 107 # undef res_init
 108 extern int __res_init_weak (void);
 109 weak_extern (__res_init_weak);
 110 strong_alias (__res_init, __res_init_weak);
 111 compat_symbol (libc, __res_init_weak, res_init, GLIBC_2_0);
 112 #endif