elf/dl-minimal.c

   1 /* Minimal replacements for basic facilities used in the dynamic linker.
   2    Copyright (C) 1995-2023 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 <assert.h>
  20 #include <ldsodefs.h>
  21 #include <dl-irel.h>
  22 #include <dl-hash.h>
  23 #include <dl-sym-post.h>
  24 #include <_itoa.h>
  25 #include <dl-minimal-malloc.h>
  26 #include <stdio.h>
  27 #include <unistd.h>
  28 #include <errno.h>
  29
  30 /* The rtld startup code calls __rtld_malloc_init_stubs after the
  31   first self-relocation to adjust the pointers to the minimal
  32   implementation below.  Before the final relocation,
  33   __rtld_malloc_init_real is called to replace the pointers with the
  34   real implementation.  */
  35 __typeof (calloc) *__rtld_calloc attribute_relro;
  36 __typeof (free) *__rtld_free attribute_relro;
  37 __typeof (malloc) *__rtld_malloc attribute_relro;
  38 __typeof (realloc) *__rtld_realloc attribute_relro;
  39
  40 void
  41 __rtld_malloc_init_stubs (void)
  42 {
  43   __rtld_calloc = &__minimal_calloc;
  44   __rtld_free = &__minimal_free;
  45   __rtld_malloc = &__minimal_malloc;
  46   __rtld_realloc = &__minimal_realloc;
  47 }
  48
  49 bool
  50 __rtld_malloc_is_complete (void)
  51 {
  52   /* The caller assumes that there is an active malloc.  */
  53   assert (__rtld_malloc != NULL);
  54   return __rtld_malloc != &__minimal_malloc;
  55 }
  56
  57 /* Lookup NAME at VERSION in the scope of MATCH.  */
  58 static void *
  59 lookup_malloc_symbol (struct link_map *main_map, const char *name,
  60                       struct r_found_version *version)
  61 {
  62
  63   const ElfW(Sym) *ref = NULL;
  64   lookup_t result = _dl_lookup_symbol_x (name, main_map, &ref,
  65                                          main_map->l_scope,
  66                                          version, 0, 0, NULL);
  67
  68   assert (ELFW(ST_TYPE) (ref->st_info) != STT_TLS);
  69   void *value = DL_SYMBOL_ADDRESS (result, ref);
  70
  71   return _dl_sym_post (result, ref, value, 0, main_map);
  72 }
  73
  74 void
  75 __rtld_malloc_init_real (struct link_map *main_map)
  76 {
  77   /* We cannot use relocations and initializers for this because the
  78      changes made by __rtld_malloc_init_stubs break REL-style
  79      (non-RELA) relocations that depend on the previous pointer
  80      contents.  Also avoid direct relocation depedencies for the
  81      malloc symbols so this function can be called before the final
  82      rtld relocation (which enables RELRO, after which the pointer
  83      variables cannot be written to).  */
  84
  85   struct r_found_version version;
  86   version.name = symbol_version_string (libc, GLIBC_2_0);
  87   version.hidden = 0;
  88   version.hash = _dl_elf_hash (version.name);
  89   version.filename = NULL;
  90
  91   void *new_calloc = lookup_malloc_symbol (main_map, "calloc", &version);
  92   void *new_free = lookup_malloc_symbol (main_map, "free", &version);
  93   void *new_malloc = lookup_malloc_symbol (main_map, "malloc", &version);
  94   void *new_realloc = lookup_malloc_symbol (main_map, "realloc", &version);
  95
  96   /* Update the pointers in one go, so that any internal allocations
  97      performed by lookup_malloc_symbol see a consistent
  98      implementation.  */
  99   __rtld_calloc = new_calloc;
 100   __rtld_free = new_free;
 101   __rtld_malloc = new_malloc;
 102   __rtld_realloc = new_realloc;
 103 }
 104
 105 \f
 106 /* Avoid signal frobnication in setjmp/longjmp.  Keeps things smaller.  */
 107
 108 #include <setjmp.h>
 109
 110 int weak_function
 111 __sigjmp_save (sigjmp_buf env, int savemask __attribute__ ((unused)))
 112 {
 113   env[0].__mask_was_saved = 0;
 114   return 0;
 115 }
 116 \f
 117 /* Define our own version of the internal function used by strerror.  We
 118    only provide the messages for some common errors.  This avoids pulling
 119    in the whole error list.  */
 120
 121 char * weak_function
 122 __strerror_r (int errnum, char *buf, size_t buflen)
 123 {
 124   char *msg;
 125
 126   switch (errnum)
 127     {
 128     case ENOMEM:
 129       msg = (char *) "Cannot allocate memory";
 130       break;
 131     case EINVAL:
 132       msg = (char *) "Invalid argument";
 133       break;
 134     case ENOENT:
 135       msg = (char *) "No such file or directory";
 136       break;
 137     case EPERM:
 138       msg = (char *) "Operation not permitted";
 139       break;
 140     case EIO:
 141       msg = (char *) "Input/output error";
 142       break;
 143     case EACCES:
 144       msg = (char *) "Permission denied";
 145       break;
 146     default:
 147       /* No need to check buffer size, all calls in the dynamic linker
 148          provide enough space.  */
 149       buf[buflen - 1] = '\0';
 150       msg = _itoa (errnum, buf + buflen - 1, 10, 0);
 151       msg = memcpy (msg - (sizeof ("Error ") - 1), "Error ",
 152                     sizeof ("Error ") - 1);
 153       break;
 154     }
 155
 156   return msg;
 157 }
 158 \f
 159 void
 160 __libc_fatal (const char *message)
 161 {
 162   _dl_fatal_printf ("%s", message);
 163 }
 164 rtld_hidden_def (__libc_fatal)
 165
 166 void
 167 __attribute__ ((noreturn))
 168 __chk_fail (void)
 169 {
 170   _exit (127);
 171 }
 172 rtld_hidden_def (__chk_fail)
 173
 174 #ifndef NDEBUG
 175 /* Define (weakly) our own assert failure function which doesn't use stdio.
 176    If we are linked into the user program (-ldl), the normal __assert_fail
 177    defn can override this one.  */
 178
 179 void weak_function
 180 __assert_fail (const char *assertion,
 181                const char *file, unsigned int line, const char *function)
 182 {
 183   _dl_fatal_printf ("\
 184 Inconsistency detected by ld.so: %s: %u: %s%sAssertion `%s' failed!\n",
 185                     file, line, function ?: "", function ? ": " : "",
 186                     assertion);
 187
 188 }
 189 # ifndef NO_RTLD_HIDDEN
 190 rtld_hidden_weak (__assert_fail)
 191 # endif
 192
 193 void weak_function
 194 __assert_perror_fail (int errnum,
 195                       const char *file, unsigned int line,
 196                       const char *function)
 197 {
 198   char errbuf[400];
 199   _dl_fatal_printf ("\
 200 Inconsistency detected by ld.so: %s: %u: %s%sUnexpected error: %s.\n",
 201                     file, line, function ?: "", function ? ": " : "",
 202                     __strerror_r (errnum, errbuf, sizeof errbuf));
 203
 204 }
 205 # ifndef NO_RTLD_HIDDEN
 206 rtld_hidden_weak (__assert_perror_fail)
 207 # endif
 208 #endif
 209 \f
 210 #undef _itoa
 211 /* We always use _itoa instead of _itoa_word in ld.so since the former
 212    also has to be present and it is never about speed when these
 213    functions are used.  */
 214 char *
 215 _itoa (unsigned long long int value, char *buflim, unsigned int base,
 216        int upper_case)
 217 {
 218   assert (! upper_case);
 219
 220   do
 221     *--buflim = _itoa_lower_digits[value % base];
 222   while ((value /= base) != 0);
 223
 224   return buflim;
 225 }
 226
 227 /* The '_itoa_lower_digits' variable in libc.so is able to handle bases
 228    up to 36.  We don't need this here.  */
 229 const char _itoa_lower_digits[16] = "0123456789abcdef";
 230 rtld_hidden_data_def (_itoa_lower_digits)
 231 \f
 232 /* The following is not a complete strsep implementation.  It cannot
 233    handle empty delimiter strings.  But this isn't necessary for the
 234    execution of ld.so.  */
 235 #undef strsep
 236 #undef __strsep
 237 char *
 238 __strsep (char **stringp, const char *delim)
 239 {
 240   char *begin;
 241
 242   assert (delim[0] != '\0');
 243
 244   begin = *stringp;
 245   if (begin != NULL)
 246     {
 247       char *end = begin;
 248
 249       while (*end != '\0' || (end = NULL))
 250         {
 251           const char *dp = delim;
 252
 253           do
 254             if (*dp == *end)
 255               break;
 256           while (*++dp != '\0');
 257
 258           if (*dp != '\0')
 259             {
 260               *end++ = '\0';
 261               break;
 262             }
 263
 264           ++end;
 265         }
 266
 267       *stringp = end;
 268     }
 269
 270   return begin;
 271 }
 272 weak_alias (__strsep, strsep)
 273 strong_alias (__strsep, __strsep_g)