stdlib/setenv.c

   1 /* Copyright (C) 1992-2015 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <http://www.gnu.org/licenses/>.  */
  17
  18 #if HAVE_CONFIG_H
  19 # include <config.h>
  20 #endif
  21
  22 #include <errno.h>
  23 #if !_LIBC
  24 # if !defined errno && !defined HAVE_ERRNO_DECL
  25 extern int errno;
  26 # endif
  27 # define __set_errno(ev) ((errno) = (ev))
  28 #endif
  29
  30 #if _LIBC || HAVE_STDLIB_H
  31 # include <stdlib.h>
  32 #endif
  33 #if _LIBC || HAVE_STRING_H
  34 # include <string.h>
  35 #endif
  36 #if _LIBC || HAVE_UNISTD_H
  37 # include <unistd.h>
  38 #endif
  39
  40 #if !_LIBC
  41 # define __environ      environ
  42 # ifndef HAVE_ENVIRON_DECL
  43 extern char **environ;
  44 # endif
  45 #endif
  46
  47 #if _LIBC
  48 /* This lock protects against simultaneous modifications of `environ'.  */
  49 # include <bits/libc-lock.h>
  50 __libc_lock_define_initialized (static, envlock)
  51 # define LOCK   __libc_lock_lock (envlock)
  52 # define UNLOCK __libc_lock_unlock (envlock)
  53 #else
  54 # define LOCK
  55 # define UNLOCK
  56 #endif
  57
  58 /* In the GNU C library we must keep the namespace clean.  */
  59 #ifdef _LIBC
  60 # define setenv __setenv
  61 # define unsetenv __unsetenv
  62 # define clearenv __clearenv
  63 # define tfind __tfind
  64 # define tsearch __tsearch
  65 #endif
  66
  67 /* In the GNU C library implementation we try to be more clever and
  68    allow arbitrarily many changes of the environment given that the used
  69    values are from a small set.  Outside glibc this will eat up all
  70    memory after a while.  */
  71 #if defined _LIBC || (defined HAVE_SEARCH_H && defined HAVE_TSEARCH \
  72                       && defined __GNUC__)
  73 # define USE_TSEARCH    1
  74 # include <search.h>
  75
  76 /* This is a pointer to the root of the search tree with the known
  77    values.  */
  78 static void *known_values;
  79
  80 # define KNOWN_VALUE(Str) \
  81   ({                                                                          \
  82     void *value = tfind (Str, &known_values, (__compar_fn_t) strcmp);         \
  83     value != NULL ? *(char **) value : NULL;                                  \
  84   })
  85 # define STORE_VALUE(Str) \
  86   tsearch (Str, &known_values, (__compar_fn_t) strcmp)
  87
  88 #else
  89 # undef USE_TSEARCH
  90
  91 # define KNOWN_VALUE(Str) NULL
  92 # define STORE_VALUE(Str) do { } while (0)
  93
  94 #endif
  95
  96
  97 /* If this variable is not a null pointer we allocated the current
  98    environment.  */
  99 static char **last_environ;
 100
 101
 102 /* This function is used by `setenv' and `putenv'.  The difference between
 103    the two functions is that for the former must create a new string which
 104    is then placed in the environment, while the argument of `putenv'
 105    must be used directly.  This is all complicated by the fact that we try
 106    to reuse values once generated for a `setenv' call since we can never
 107    free the strings.  */
 108 int
 109 __add_to_environ (name, value, combined, replace)
 110      const char *name;
 111      const char *value;
 112      const char *combined;
 113      int replace;
 114 {
 115   char **ep;
 116   size_t size;
 117   const size_t namelen = strlen (name);
 118   const size_t vallen = value != NULL ? strlen (value) + 1 : 0;
 119
 120   LOCK;
 121
 122   /* We have to get the pointer now that we have the lock and not earlier
 123      since another thread might have created a new environment.  */
 124   ep = __environ;
 125
 126   size = 0;
 127   if (ep != NULL)
 128     {
 129       for (; *ep != NULL; ++ep)
 130         if (!strncmp (*ep, name, namelen) && (*ep)[namelen] == '=')
 131           break;
 132         else
 133           ++size;
 134     }
 135
 136   if (ep == NULL || __builtin_expect (*ep == NULL, 1))
 137     {
 138       char **new_environ;
 139
 140       /* We allocated this space; we can extend it.  */
 141       new_environ = (char **) realloc (last_environ,
 142                                        (size + 2) * sizeof (char *));
 143       if (new_environ == NULL)
 144         {
 145           UNLOCK;
 146           return -1;
 147         }
 148
 149       if (__environ != last_environ)
 150         memcpy ((char *) new_environ, (char *) __environ,
 151                 size * sizeof (char *));
 152
 153       new_environ[size] = NULL;
 154       new_environ[size + 1] = NULL;
 155       ep = new_environ + size;
 156
 157       last_environ = __environ = new_environ;
 158     }
 159   if (*ep == NULL || replace)
 160     {
 161       char *np;
 162
 163       /* Use the user string if given.  */
 164       if (combined != NULL)
 165         np = (char *) combined;
 166       else
 167         {
 168           const size_t varlen = namelen + 1 + vallen;
 169 #ifdef USE_TSEARCH
 170           char *new_value;
 171           int use_alloca = __libc_use_alloca (varlen);
 172           if (__builtin_expect (use_alloca, 1))
 173             new_value = (char *) alloca (varlen);
 174           else
 175             {
 176               new_value = malloc (varlen);
 177               if (new_value == NULL)
 178                 {
 179                   UNLOCK;
 180                   return -1;
 181                 }
 182             }
 183 # ifdef _LIBC
 184           __mempcpy (__mempcpy (__mempcpy (new_value, name, namelen), "=", 1),
 185                      value, vallen);
 186 # else
 187           memcpy (new_value, name, namelen);
 188           new_value[namelen] = '=';
 189           memcpy (&new_value[namelen + 1], value, vallen);
 190 # endif
 191
 192           np = KNOWN_VALUE (new_value);
 193           if (__glibc_likely (np == NULL))
 194 #endif
 195             {
 196 #ifdef USE_TSEARCH
 197               if (__glibc_unlikely (! use_alloca))
 198                 np = new_value;
 199               else
 200 #endif
 201                 {
 202                   np = malloc (varlen);
 203                   if (__glibc_unlikely (np == NULL))
 204                     {
 205                       UNLOCK;
 206                       return -1;
 207                     }
 208
 209 #ifdef USE_TSEARCH
 210                   memcpy (np, new_value, varlen);
 211 #else
 212                   memcpy (np, name, namelen);
 213                   np[namelen] = '=';
 214                   memcpy (&np[namelen + 1], value, vallen);
 215 #endif
 216                 }
 217               /* And remember the value.  */
 218               STORE_VALUE (np);
 219             }
 220         }
 221
 222       *ep = np;
 223     }
 224
 225   UNLOCK;
 226
 227   return 0;
 228 }
 229
 230 int
 231 setenv (name, value, replace)
 232      const char *name;
 233      const char *value;
 234      int replace;
 235 {
 236   if (name == NULL || *name == '\0' || strchr (name, '=') != NULL)
 237     {
 238       __set_errno (EINVAL);
 239       return -1;
 240     }
 241
 242   return __add_to_environ (name, value, NULL, replace);
 243 }
 244
 245 int
 246 unsetenv (name)
 247      const char *name;
 248 {
 249   size_t len;
 250   char **ep;
 251
 252   if (name == NULL || *name == '\0' || strchr (name, '=') != NULL)
 253     {
 254       __set_errno (EINVAL);
 255       return -1;
 256     }
 257
 258   len = strlen (name);
 259
 260   LOCK;
 261
 262   ep = __environ;
 263   if (ep != NULL)
 264     while (*ep != NULL)
 265       if (!strncmp (*ep, name, len) && (*ep)[len] == '=')
 266         {
 267           /* Found it.  Remove this pointer by moving later ones back.  */
 268           char **dp = ep;
 269
 270           do
 271             dp[0] = dp[1];
 272           while (*dp++);
 273           /* Continue the loop in case NAME appears again.  */
 274         }
 275       else
 276         ++ep;
 277
 278   UNLOCK;
 279
 280   return 0;
 281 }
 282
 283 /* The `clearenv' was planned to be added to POSIX.1 but probably
 284    never made it.  Nevertheless the POSIX.9 standard (POSIX bindings
 285    for Fortran 77) requires this function.  */
 286 int
 287 clearenv (void)
 288 {
 289   LOCK;
 290
 291   if (__environ == last_environ && __environ != NULL)
 292     {
 293       /* We allocated this environment so we can free it.  */
 294       free (__environ);
 295       last_environ = NULL;
 296     }
 297
 298   /* Clear the environment pointer removes the whole environment.  */
 299   __environ = NULL;
 300
 301   UNLOCK;
 302
 303   return 0;
 304 }
 305 #ifdef _LIBC
 306 libc_freeres_fn (free_mem)
 307 {
 308   /* Remove all traces.  */
 309   clearenv ();
 310
 311   /* Now remove the search tree.  */
 312   __tdestroy (known_values, free);
 313   known_values = NULL;
 314 }
 315
 316 # undef setenv
 317 # undef unsetenv
 318 # undef clearenv
 319 weak_alias (__setenv, setenv)
 320 weak_alias (__unsetenv, unsetenv)
 321 weak_alias (__clearenv, clearenv)
 322 #endif