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 _dlerror_run (void (*operate) (void *), void *args)
 124 {
 125   struct dl_action_result *result;
 126
 127   /* If we have not yet initialized the buffer do it now.  */
 128   __libc_once (once, init);
 129
 130   /* Get error string and number.  */
 131   if (static_buf != NULL)
 132     result = static_buf;
 133   else
 134     {
 135       /* We don't use the static buffer and so we have a key.  Use it
 136          to get the thread-specific buffer.  */
 137       result = __libc_getspecific (key);
 138       if (result == NULL)
 139         {
 140           result = (struct dl_action_result *) calloc (1, sizeof (*result));
 141           if (result == NULL)
 142             /* We are out of memory.  Since this is no really critical
 143                situation we carry on by using the global variable.
 144                This might lead to conflicts between the threads but
 145                they soon all will have memory problems.  */
 146             result = &last_result;
 147           else
 148             /* Set the tsd.  */
 149             __libc_setspecific (key, result);
 150         }
 151     }
 152
 153   if (result->errstring != NULL)
 154     {
 155       /* Free the error string from the last failed command.  This can
 156          happen if `dlerror' was not run after an error was found.  */
 157       if (result->malloced)
 158         free ((char *) result->errstring);
 159       result->errstring = NULL;
 160     }
 161
 162   result->errcode = _dl_catch_error (&result->objname, &result->errstring,
 163                                      &result->malloced, operate, args);
 164
 165   /* If no error we mark that no error string is available.  */
 166   result->returned = result->errstring == NULL;
 167
 168   return result->errstring != NULL;
 169 }
 170
 171
 172 /* Initialize buffers for results.  */
 173 static void
 174 init (void)
 175 {
 176   if (__libc_key_create (&key, free_key_mem))
 177     /* Creating the key failed.  This means something really went
 178        wrong.  In any case use a static buffer which is better than
 179        nothing.  */
 180     static_buf = &last_result;
 181 }
 182
 183
 184 static void
 185 check_free (struct dl_action_result *rec)
 186 {
 187   if (rec->errstring != NULL
 188       && strcmp (rec->errstring, "out of memory") != 0)
 189     {
 190       /* We can free the string only if the allocation happened in the
 191          C library used by the dynamic linker.  This means, it is
 192          always the C library in the base namespace.  When we're statically
 193          linked, the dynamic linker is part of the program and so always
 194          uses the same C library we use here.  */
 195 #ifdef SHARED
 196       struct link_map *map = NULL;
 197       Dl_info info;
 198       if (_dl_addr (check_free, &info, &map, NULL) != 0 && map->l_ns == 0)
 199 #endif
 200         free ((char *) rec->errstring);
 201     }
 202 }
 203
 204
 205 static void
 206 __attribute__ ((destructor))
 207 fini (void)
 208 {
 209   check_free (&last_result);
 210 }
 211
 212
 213 /* Free the thread specific data, this is done if a thread terminates.  */
 214 static void
 215 free_key_mem (void *mem)
 216 {
 217   check_free ((struct dl_action_result *) mem);
 218
 219   free (mem);
 220   __libc_setspecific (key, NULL);
 221 }
 222
 223 # ifdef SHARED
 224
 225 struct dlfcn_hook *_dlfcn_hook __attribute__((nocommon));
 226 libdl_hidden_data_def (_dlfcn_hook)
 227
 228 # else
 229
 230 static struct dlfcn_hook _dlfcn_hooks =
 231   {
 232     .dlopen = __dlopen,
 233     .dlclose = __dlclose,
 234     .dlsym = __dlsym,
 235     .dlvsym = __dlvsym,
 236     .dlerror = __dlerror,
 237     .dladdr = __dladdr,
 238     .dladdr1 = __dladdr1,
 239     .dlinfo = __dlinfo,
 240     .dlmopen = __dlmopen
 241   };
 242
 243 void
 244 __libc_register_dlfcn_hook (struct link_map *map)
 245 {
 246   struct dlfcn_hook **hook;
 247
 248   hook = (struct dlfcn_hook **) __libc_dlsym_private (map, "_dlfcn_hook");
 249   if (hook != NULL)
 250     *hook = &_dlfcn_hooks;
 251 }
 252 # endif
 253 #endif