dlfcn/dlerror.c

   1 /* Return error detail for failing <dlfcn.h> functions.
   2    Copyright (C) 1995-2021 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    <https://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 #include <libc-symbols.h>
  28
  29 #if !defined SHARED && IS_IN (libdl)
  30
  31 char *
  32 dlerror (void)
  33 {
  34   return __dlerror ();
  35 }
  36
  37 #else
  38
  39 /* Type for storing results of dynamic loading actions.  */
  40 struct dl_action_result
  41   {
  42     int errcode;
  43     int returned;
  44     bool malloced;
  45     const char *objname;
  46     const char *errstring;
  47   };
  48 static struct dl_action_result last_result;
  49 static struct dl_action_result *static_buf;
  50
  51 /* This is the key for the thread specific memory.  */
  52 static __libc_key_t key;
  53 __libc_once_define (static, once);
  54
  55 /* Destructor for the thread-specific data.  */
  56 static void init (void);
  57 static void free_key_mem (void *mem);
  58
  59
  60 char *
  61 __dlerror (void)
  62 {
  63   char *buf = NULL;
  64   struct dl_action_result *result;
  65
  66 # ifdef SHARED
  67   if (!rtld_active ())
  68     return _dlfcn_hook->dlerror ();
  69 # endif
  70
  71   /* If we have not yet initialized the buffer do it now.  */
  72   __libc_once (once, init);
  73
  74   /* Get error string.  */
  75   if (static_buf != NULL)
  76     result = static_buf;
  77   else
  78     {
  79       /* init () has been run and we don't use the static buffer.
  80          So we have a valid key.  */
  81       result = (struct dl_action_result *) __libc_getspecific (key);
  82       if (result == NULL)
  83         result = &last_result;
  84     }
  85
  86   /* Test whether we already returned the string.  */
  87   if (result->returned != 0)
  88     {
  89       /* We can now free the string.  */
  90       if (result->errstring != NULL)
  91         {
  92           if (strcmp (result->errstring, "out of memory") != 0)
  93             free ((char *) result->errstring);
  94           result->errstring = NULL;
  95         }
  96     }
  97   else if (result->errstring != NULL)
  98     {
  99       buf = (char *) result->errstring;
 100       int n;
 101       if (result->errcode == 0)
 102         n = __asprintf (&buf, "%s%s%s",
 103                         result->objname,
 104                         result->objname[0] == '\0' ? "" : ": ",
 105                         _(result->errstring));
 106       else
 107         n = __asprintf (&buf, "%s%s%s: %s",
 108                         result->objname,
 109                         result->objname[0] == '\0' ? "" : ": ",
 110                         _(result->errstring),
 111                         strerror (result->errcode));
 112       if (n != -1)
 113         {
 114           /* We don't need the error string anymore.  */
 115           if (strcmp (result->errstring, "out of memory") != 0)
 116             free ((char *) result->errstring);
 117           result->errstring = buf;
 118         }
 119
 120       /* Mark the error as returned.  */
 121       result->returned = 1;
 122     }
 123
 124   return buf;
 125 }
 126 # ifdef SHARED
 127 strong_alias (__dlerror, dlerror)
 128 # endif
 129
 130 int
 131 _dlerror_run (void (*operate) (void *), void *args)
 132 {
 133   struct dl_action_result *result;
 134
 135   /* If we have not yet initialized the buffer do it now.  */
 136   __libc_once (once, init);
 137
 138   /* Get error string and number.  */
 139   if (static_buf != NULL)
 140     result = static_buf;
 141   else
 142     {
 143       /* We don't use the static buffer and so we have a key.  Use it
 144          to get the thread-specific buffer.  */
 145       result = __libc_getspecific (key);
 146       if (result == NULL)
 147         {
 148           result = (struct dl_action_result *) calloc (1, sizeof (*result));
 149           if (result == NULL)
 150             /* We are out of memory.  Since this is no really critical
 151                situation we carry on by using the global variable.
 152                This might lead to conflicts between the threads but
 153                they soon all will have memory problems.  */
 154             result = &last_result;
 155           else
 156             /* Set the tsd.  */
 157             __libc_setspecific (key, result);
 158         }
 159     }
 160
 161   if (result->errstring != NULL)
 162     {
 163       /* Free the error string from the last failed command.  This can
 164          happen if `dlerror' was not run after an error was found.  */
 165       if (result->malloced)
 166         free ((char *) result->errstring);
 167       result->errstring = NULL;
 168     }
 169
 170   result->errcode = _dl_catch_error (&result->objname, &result->errstring,
 171                                      &result->malloced, operate, args);
 172
 173   /* If no error we mark that no error string is available.  */
 174   result->returned = result->errstring == NULL;
 175
 176   return result->errstring != NULL;
 177 }
 178
 179
 180 /* Initialize buffers for results.  */
 181 static void
 182 init (void)
 183 {
 184   if (__libc_key_create (&key, free_key_mem))
 185     /* Creating the key failed.  This means something really went
 186        wrong.  In any case use a static buffer which is better than
 187        nothing.  */
 188     static_buf = &last_result;
 189 }
 190
 191
 192 static void
 193 check_free (struct dl_action_result *rec)
 194 {
 195   if (rec->errstring != NULL
 196       && strcmp (rec->errstring, "out of memory") != 0)
 197     {
 198       /* We can free the string only if the allocation happened in the
 199          C library used by the dynamic linker.  This means, it is
 200          always the C library in the base namespace.  When we're statically
 201          linked, the dynamic linker is part of the program and so always
 202          uses the same C library we use here.  */
 203 #ifdef SHARED
 204       struct link_map *map = NULL;
 205       Dl_info info;
 206       if (_dl_addr (check_free, &info, &map, NULL) != 0 && map->l_ns == 0)
 207 #endif
 208         {
 209           free ((char *) rec->errstring);
 210           rec->errstring = NULL;
 211         }
 212     }
 213 }
 214
 215
 216 static void
 217 __attribute__ ((destructor))
 218 fini (void)
 219 {
 220   check_free (&last_result);
 221 }
 222
 223
 224 /* Free the thread specific data, this is done if a thread terminates.  */
 225 static void
 226 free_key_mem (void *mem)
 227 {
 228   check_free ((struct dl_action_result *) mem);
 229
 230   free (mem);
 231   __libc_setspecific (key, NULL);
 232 }
 233
 234 # ifdef SHARED
 235
 236 /* Free the dlerror-related resources.  */
 237 void
 238 __dlerror_main_freeres (void)
 239 {
 240   /* Free the global memory if used.  */
 241   check_free (&last_result);
 242
 243   if (__libc_once_get (once) && static_buf == NULL)
 244     {
 245       /* init () has been run and we don't use the static buffer.
 246          So we have a valid key.  */
 247       void *mem;
 248       /* Free the TSD memory if used.  */
 249       mem = __libc_getspecific (key);
 250       if (mem != NULL)
 251         free_key_mem (mem);
 252     }
 253 }
 254
 255 struct dlfcn_hook *_dlfcn_hook __attribute__((nocommon));
 256 libdl_hidden_data_def (_dlfcn_hook)
 257
 258 # else
 259
 260 static struct dlfcn_hook _dlfcn_hooks =
 261   {
 262     .dlopen = __dlopen,
 263     .dlclose = __dlclose,
 264     .dlsym = __dlsym,
 265     .dlvsym = __dlvsym,
 266     .dlerror = __dlerror,
 267     .dladdr = __dladdr,
 268     .dladdr1 = __dladdr1,
 269     .dlinfo = __dlinfo,
 270     .dlmopen = __dlmopen
 271   };
 272
 273 void
 274 __libc_register_dlfcn_hook (struct link_map *map)
 275 {
 276   struct dlfcn_hook **hook;
 277
 278   hook = (struct dlfcn_hook **) __libc_dlsym_private (map, "_dlfcn_hook");
 279   if (hook != NULL)
 280     *hook = &_dlfcn_hooks;
 281 }
 282 # endif
 283 #endif