elf/rtld.c

   1 /* Run time dynamic linker.
   2 Copyright (C) 1995 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 Library General Public License as
   7 published by the Free Software Foundation; either version 2 of the
   8 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 Library General Public License for more details.
  14
  15 You should have received a copy of the GNU Library General Public
  16 License along with the GNU C Library; see the file COPYING.LIB.  If
  17 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  18 Cambridge, MA 02139, USA.  */
  19
  20 #include <link.h>
  21 #include "dynamic-link.h"
  22 #include <stddef.h>
  23 #include <stdlib.h>
  24 #include <unistd.h>
  25
  26
  27 #ifdef RTLD_START
  28 RTLD_START
  29 #else
  30 #error "sysdeps/MACHINE/dl-machine.h fails to define RTLD_START"
  31 #endif
  32
  33 /* System-specific function to do initial startup for the dynamic linker.
  34    After this, file access calls and getenv must work.  This is responsible
  35    for setting _dl_secure if we need to be secure (e.g. setuid),
  36    and for setting _dl_argc and _dl_argv, and then calling _dl_main.  */
  37 extern Elf32_Addr _dl_sysdep_start (void **start_argptr,
  38                                     void (*dl_main) (const Elf32_Phdr *phdr,
  39                                                      Elf32_Word phent,
  40                                                      Elf32_Addr *user_entry));
  41
  42 int _dl_secure;
  43 int _dl_argc;
  44 char **_dl_argv;
  45
  46 struct r_debug dl_r_debug;
  47
  48 static void dl_main (const Elf32_Phdr *phdr,
  49                      Elf32_Word phent,
  50                      Elf32_Addr *user_entry);
  51
  52 Elf32_Addr
  53 _dl_start (void *arg)
  54 {
  55   struct link_map rtld_map;
  56
  57   /* Figure out the run-time load address of the dynamic linker itself.  */
  58   rtld_map.l_addr = elf_machine_load_address ();
  59
  60   /* Read our own dynamic section and fill in the info array.
  61      Conveniently, the first element of the GOT contains the
  62      offset of _DYNAMIC relative to the run-time load address.  */
  63   rtld_map.l_ld = (void *) rtld_map.l_addr + *elf_machine_got ();
  64   elf_get_dynamic_info (rtld_map.l_ld, rtld_map.l_info);
  65
  66 #ifdef ELF_MACHINE_BEFORE_RTLD_RELOC
  67   ELF_MACHINE_BEFORE_RTLD_RELOC (rtld_map.l_info);
  68 #endif
  69
  70   /* Relocate ourselves so we can do normal function calls and
  71      data access using the global offset table.  */
  72
  73   ELF_DYNAMIC_RELOCATE (&rtld_map, 0, NULL);
  74
  75
  76   /* Now life is sane; we can call functions and access global data.
  77      Set up to use the operating system facilities, and find out from
  78      the operating system's program loader where to find the program
  79      header table in core.  */
  80
  81   dl_r_debug.r_ldbase = rtld_map.l_addr; /* Record our load address.  */
  82
  83   /* Call the OS-dependent function to set up life so we can do things like
  84      file access.  It will call `dl_main' (below) to do all the real work
  85      of the dynamic linker, and then unwind our frame and run the user
  86      entry point on the same stack we entered on.  */
  87   return _dl_sysdep_start (&arg, &dl_main);
  88 }
  89
  90
  91 /* Now life is peachy; we can do all normal operations.
  92    On to the real work.  */
  93
  94 void _start (void);
  95
  96 static int rtld_command;        /* Nonzero if we were run directly.  */
  97
  98 static void
  99 dl_main (const Elf32_Phdr *phdr,
 100          Elf32_Word phent,
 101          Elf32_Addr *user_entry)
 102 {
 103   void doit (void)
 104     {
 105       const Elf32_Phdr *ph;
 106       struct link_map *l;
 107       const char *interpreter_name;
 108       int lazy;
 109
 110       if (*user_entry == (Elf32_Addr) &_start)
 111         {
 112           /* Ho ho.  We are not the program interpreter!  We are the program
 113              itself!  This means someone ran ld.so as a command.  Well, that
 114              might be convenient to do sometimes.  We support it by
 115              interpreting the args like this:
 116
 117              ld.so PROGRAM ARGS...
 118
 119              The first argument is the name of a file containing an ELF
 120              executable we will load and run with the following arguments.
 121              To simplify life here, PROGRAM is searched for using the
 122              normal rules for shared objects, rather than $PATH or anything
 123              like that.  We just load it and use its entry point; we don't
 124              pay attention to its PT_INTERP command (we are the interpreter
 125              ourselves).  This is an easy way to test a new ld.so before
 126              installing it.  */
 127           if (_dl_argc < 2)
 128             _dl_sysdep_fatal ("\
 129 Usage: ld.so EXECUTABLE-FILE [ARGS-FOR-PROGRAM...]\n\
 130 You have invoked `ld.so', the helper program for shared library executables.\n\
 131 This program usually lives in the file `/lib/ld.so', and special directives\n\
 132 in executable files using ELF shared libraries tell the system's program\n\
 133 loader to load the helper program from this file.  This helper program loads\n\
 134 the shared libraries needed by the program executable, prepares the program\n\
 135 to run, and runs it.  You may invoke this helper program directly from the\n\
 136 command line to load and run an ELF executable file; this is like executing\n\
 137 that file itself, but always uses this helper program from the file you\n\
 138 specified, instead of the helper program file specified in the executable\n\
 139 file you run.  This is mostly of use for maintainers to test new versions\n\
 140 of this helper program; chances are you did not intend to run this program.\n"
 141                               );
 142
 143           rtld_command = 1;
 144           interpreter_name = _dl_argv[0];
 145           --_dl_argc;
 146           ++_dl_argv;
 147           l = _dl_map_object (NULL, _dl_argv[0], user_entry);
 148           phdr = l->l_phdr;
 149           phent = l->l_phnum;
 150           l->l_type = lt_executable;
 151           l->l_libname = (char *) "";
 152         }
 153       else
 154         {
 155           /* Create a link_map for the executable itself.
 156              This will be what dlopen on "" returns.  */
 157           l = _dl_new_object ((char *) "", "", lt_executable);
 158           l->l_phdr = phdr;
 159           l->l_phnum = phent;
 160           interpreter_name = 0;
 161         }
 162
 163       /* Scan the program header table for the dynamic section.  */
 164       for (ph = phdr; ph < &phdr[phent]; ++ph)
 165         switch (ph->p_type)
 166           {
 167           case PT_DYNAMIC:
 168             /* This tells us where to find the dynamic section,
 169                which tells us everything we need to do.  */
 170             l->l_ld = (void *) l->l_addr + ph->p_vaddr;
 171             break;
 172           case PT_INTERP:
 173             /* This "interpreter segment" was used by the program loader to
 174                find the program interpreter, which is this program itself, the
 175                dynamic linker.  We note what name finds us, so that a future
 176                dlopen call or DT_NEEDED entry, for something that wants to link
 177                against the dynamic linker as a shared library, will know that
 178                the shared object is already loaded.  */
 179             interpreter_name = (void *) l->l_addr + ph->p_vaddr;
 180             break;
 181           }
 182       assert (interpreter_name); /* How else did we get here?  */
 183
 184       /* Extract the contents of the dynamic section for easy access.  */
 185       elf_get_dynamic_info (l->l_ld, l->l_info);
 186       /* Set up our cache of pointers into the hash table.  */
 187       _dl_setup_hash (l);
 188
 189       if (l->l_info[DT_DEBUG])
 190         /* There is a DT_DEBUG entry in the dynamic section.  Fill it in
 191            with the run-time address of the r_debug structure, which we
 192            will set up later to communicate with the debugger.  */
 193         l->l_info[DT_DEBUG]->d_un.d_ptr = (Elf32_Addr) &dl_r_debug;
 194
 195       l = _dl_new_object ((char *) interpreter_name, interpreter_name,
 196                           lt_interpreter);
 197
 198       /* Now process all the DT_NEEDED entries and map in the objects.
 199          Each new link_map will go on the end of the chain, so we will
 200          come across it later in the loop to map in its dependencies.  */
 201       for (l = _dl_loaded; l; l = l->l_next)
 202         {
 203           if (l->l_info[DT_NEEDED])
 204             {
 205               const char *strtab
 206                 = (void *) l->l_addr + l->l_info[DT_STRTAB]->d_un.d_ptr;
 207               const Elf32_Dyn *d;
 208               for (d = l->l_ld; d->d_tag != DT_NULL; ++d)
 209                 if (d->d_tag == DT_NEEDED)
 210                   _dl_map_object (l, strtab + d->d_un.d_val, NULL);
 211             }
 212           l->l_deps_loaded = 1;
 213         }
 214
 215       l = _dl_loaded->l_next;
 216       assert (l->l_type == lt_interpreter);
 217       if (l->l_opencount == 0)
 218         {
 219           /* No DT_NEEDED entry referred to the interpreter object itself.
 220              Remove it from the maps we will use for symbol resolution.  */
 221           l->l_prev->l_next = l->l_next;
 222           if (l->l_next)
 223             l->l_next->l_prev = l->l_prev;
 224         }
 225
 226       lazy = !_dl_secure && *(getenv ("LD_BIND_NOW") ?: "") == '\0';
 227
 228       /* Now we have all the objects loaded.  Relocate them all.
 229          We do this in reverse order so that copy relocs of earlier
 230          objects overwrite the data written by later objects.  */
 231       l = _dl_loaded;
 232       while (l->l_next)
 233         l = l->l_next;
 234       do
 235         {
 236           _dl_relocate_object (l, lazy);
 237           l = l->l_prev;
 238         } while (l);
 239
 240       /* Tell the debugger where to find the map of loaded objects.  */
 241       dl_r_debug.r_version = 1  /* R_DEBUG_VERSION XXX */;
 242       dl_r_debug.r_map = _dl_loaded;
 243       dl_r_debug.r_brk = (Elf32_Addr) &_dl_r_debug_state;
 244     }
 245   const char *errstring;
 246   const char *errobj;
 247   int err;
 248
 249   err = _dl_catch_error (&errstring, &errobj, &doit);
 250   if (errstring)
 251     _dl_sysdep_fatal (_dl_argv[0] ?: "<program name unknown>",
 252                       ": error in loading shared libraries\n",
 253                       errobj ?: "", errobj ? ": " : "",
 254                       errstring, err ? ": " : NULL,
 255                       err ? strerror (err) : NULL, NULL);
 256
 257   /* Once we return, _dl_sysdep_start will invoke
 258      the DT_INIT functions and then *USER_ENTRY.  */
 259 }
 260
 261 /* This function exists solely to have a breakpoint set on it by the
 262    debugger.  */
 263 void
 264 _dl_r_debug_state (void)
 265 {
 266 }
 267 \f
 268 #ifndef NDEBUG
 269
 270 /* Define (weakly) our own assert failure function which doesn't use stdio.
 271    If we are linked into the user program (-ldl), the normal __assert_fail
 272    defn can override this one.  */
 273
 274 #include "../stdio/_itoa.h"
 275
 276 void
 277 __assert_fail (const char *assertion,
 278                const char *file, unsigned int line, const char *function)
 279 {
 280   char buf[64];
 281   buf[sizeof buf - 1] = '\0';
 282   _dl_sysdep_fatal ("BUG IN DYNAMIC LINKER ld.so: ",
 283                     file, ": ", _itoa (line, buf + sizeof buf - 1, 10, 0),
 284                     ": ", function ?: "", function ? ": " : "",
 285                     "Assertion `", assertion, "' failed!\n");
 286
 287 }
 288 weak_symbol (__assert_fail)
 289
 290 #endif