dlfcn/dlerror.c

   1 /* Return error detail for failing <dlfcn.h> functions.
   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 #include <dlfcn.h>
  20 #include <libintl.h>
  21 #include <stdbool.h>
  22 #include <stdio.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <libc-lock.h>
  26 #include <ldsodefs.h>
  27
  28 #if !defined SHARED && IS_IN (libdl)
  29
  30 char *
  31 dlerror (void)
  32 {
  33   return __dlerror ();
  34 }
  35
  36 #else
  37
  38 /* Type for storing results of dynamic loading actions.  */
  39 struct dl_action_result
  40   {
  41     int errcode;
  42     int returned;
  43     bool malloced;
  44     const char *objname;
  45     const char *errstring;
  46   };
  47 static struct dl_action_result last_result;
  48 static struct dl_action_result *static_buf;
  49
  50 /* This is the key for the thread specific memory.  */
  51 static __libc_key_t key;
  52 __libc_once_define (static, once);
  53
  54 /* Destructor for the thread-specific data.  */
  55 static void init (void);
  56 static void free_key_mem (void *mem);
  57
  58
  59 char *
  60 __dlerror (void)
  61 {
  62   char *buf = NULL;
  63   struct dl_action_result *result;
  64
  65 # ifdef SHARED
  66   if (__glibc_unlikely (_dlfcn_hook != NULL))
  67     return _dlfcn_hook->dlerror ();
  68 # endif
  69
  70   /* If we have not yet initialized the buffer do it now.  */
  71   __libc_once (once, init);
  72
  73   /* Get error string.  */
  74   result = (struct dl_action_result *) __libc_getspecific (key);
  75   if (result == NULL)
  76     result = &last_result;
  77
  78   /* Test whether we already returned the string.  */
  79   if (result->returned != 0)
  80     {
  81       /* We can now free the string.  */
  82       if (result->errstring != NULL)
  83         {
  84           if (strcmp (result->errstring, "out of memory") != 0)
  85             free ((char *) result->errstring);
  86           result->errstring = NULL;
  87         }
  88     }
  89   else if (result->errstring != NULL)
  90     {
  91       buf = (char *) result->errstring;
  92       int n;
  93       if (result->errcode == 0)
  94         n = __asprintf (&buf, "%s%s%s",
  95                         result->objname,
  96                         result->objname[0] == '\0' ? "" : ": ",
  97                         _(result->errstring));
  98       else
  99         n = __asprintf (&buf, "%s%s%s: %s",
 100                         result->objname,
 101                         result->objname[0] == '\0' ? "" : ": ",
 102                         _(result->errstring),
 103                         strerror (result->errcode));
 104       if (n != -1)
 105         {
 106           /* We don't need the error string anymore.  */
 107           if (strcmp (result->errstring, "out of memory") != 0)
 108             free ((char *) result->errstring);
 109           result->errstring = buf;
 110         }
 111
 112       /* Mark the error as returned.  */
 113       result->returned = 1;
 114     }
 115
 116   return buf;
 117 }
 118 # ifdef SHARED
 119 strong_alias (__dlerror, dlerror)
 120 # endif
 121
 122 int
 123 internal_function
 124 _dlerror_run (void (*operate) (void *), void *args)
 125 {
 126   struct dl_action_result *result;
 127
 128   /* If we have not yet initialized the buffer do it now.  */
 129   __libc_once (once, init);
 130
 131   /* Get error string and number.  */
 132   if (static_buf != NULL)
 133     result = static_buf;
 134   else
 135     {
 136       /* We don't use the static buffer and so we have a key.  Use it
 137          to get the thread-specific buffer.  */
 138       result = __libc_getspecific (key);
 139       if (result == NULL)
 140         {
 141           result = (struct dl_action_result *) calloc (1, sizeof (*result));
 142           if (result == NULL)
 143             /* We are out of memory.  Since this is no really critical
 144                situation we carry on by using the global variable.
 145                This might lead to conflicts between the threads but
 146                they soon all will have memory problems.  */
 147             result = &last_result;
 148           else
 149             /* Set the tsd.  */
 150             __libc_setspecific (key, result);
 151         }
 152     }
 153
 154   if (result->errstring != NULL)
 155     {
 156       /* Free the error string from the last failed command.  This can
 157          happen if `dlerror' was not run after an error was found.  */
 158       if (result->malloced)
 159         free ((char *) result->errstring);
 160       result->errstring = NULL;
 161     }
 162
 163   result->errcode = _dl_catch_error (&result->objname, &result->errstring,
 164                                      &result->malloced, operate, args);
 165
 166   /* If no error we mark that no error string is available.  */
 167   result->returned = result->errstring == NULL;
 168
 169   return result->errstring != NULL;
 170 }
 171
 172
 173 /* Initialize buffers for results.  */
 174 static void
 175 init (void)
 176 {
 177   if (__libc_key_create (&key, free_key_mem))
 178     /* Creating the key failed.  This means something really went
 179        wrong.  In any case use a static buffer which is better than
 180        nothing.  */
 181     static_buf = &last_result;
 182 }
 183
 184
 185 static void
 186 check_free (struct dl_action_result *rec)
 187 {
 188   if (rec->errstring != NULL
 189       && strcmp (rec->errstring, "out of memory") != 0)
 190     {
 191       /* We can free the string only if the allocation happened in the
 192          C library used by the dynamic linker.  This means, it is
 193          always the C library in the base namespace.  When we're statically
 194          linked, the dynamic linker is part of the program and so always
 195          uses the same C library we use here.  */
 196 #ifdef SHARED
 197       struct link_map *map = NULL;
 198       Dl_info info;
 199       if (_dl_addr (check_free, &info, &map, NULL) != 0 && map->l_ns == 0)
 200 #endif
 201         free ((char *) rec->errstring);
 202     }
 203 }
 204
 205
 206 static void
 207 __attribute__ ((destructor))
 208 fini (void)
 209 {
 210   check_free (&last_result);
 211 }
 212
 213
 214 /* Free the thread specific data, this is done if a thread terminates.  */
 215 static void
 216 free_key_mem (void *mem)
 217 {
 218   check_free ((struct dl_action_result *) mem);
 219
 220   free (mem);
 221   __libc_setspecific (key, NULL);
 222 }
 223
 224 # ifdef SHARED
 225
 226 struct dlfcn_hook *_dlfcn_hook __attribute__((nocommon));
 227 libdl_hidden_data_def (_dlfcn_hook)
 228
 229 # else
 230
 231 static struct dlfcn_hook _dlfcn_hooks =
 232   {
 233     .dlopen = __dlopen,
 234     .dlclose = __dlclose,
 235     .dlsym = __dlsym,
 236     .dlvsym = __dlvsym,
 237     .dlerror = __dlerror,
 238     .dladdr = __dladdr,
 239     .dladdr1 = __dladdr1,
 240     .dlinfo = __dlinfo,
 241     .dlmopen = __dlmopen
 242   };
 243
 244 void
 245 __libc_register_dlfcn_hook (struct link_map *map)
 246 {
 247   struct dlfcn_hook **hook;
 248
 249   hook = (struct dlfcn_hook **) __libc_dlsym_private (map, "_dlfcn_hook");
 250   if (hook != NULL)
 251     *hook = &_dlfcn_hooks;
 252 }
 253 # endif
 254 #endif