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 void
  97 dl_main (const Elf32_Phdr *phdr,
  98          Elf32_Word phent,
  99          Elf32_Addr *user_entry)
 100 {
 101   void doit (void)
 102     {
 103       const Elf32_Phdr *ph;
 104       struct link_map *l;
 105       const char *interpreter_name;
 106       int lazy;
 107
 108       if (*user_entry == (Elf32_Addr) &_start)
 109         {
 110           /* Ho ho.  We are not the program interpreter!  We are the program
 111              itself!  This means someone ran ld.so as a command.  Well, that
 112              might be convenient to do sometimes.  We support it by
 113              interpreting the args like this:
 114
 115              ld.so PROGRAM ARGS...
 116
 117              The first argument is the name of a file containing an ELF
 118              executable we will load and run with the following arguments.
 119              To simplify life here, PROGRAM is searched for using the
 120              normal rules for shared objects, rather than $PATH or anything
 121              like that.  We just load it and use its entry point; we don't
 122              pay attention to its PT_INTERP command (we are the interpreter
 123              ourselves).  This is an easy way to test a new ld.so before
 124              installing it.  */
 125           if (_dl_argc < 2)
 126             _dl_sysdep_fatal ("\
 127 Usage: ld.so EXECUTABLE-FILE [ARGS-FOR-PROGRAM...]\n\
 128 You have invoked `ld.so', the helper program for shared library executables.\n\
 129 This program usually lives in the file `/lib/ld.so', and special directives\n\
 130 in executable files using ELF shared libraries tell the system's program\n\
 131 loader to load the helper program from this file.  This helper program loads\n\
 132 the shared libraries needed by the program executable, prepares the program\n\
 133 to run, and runs it.  You may invoke this helper program directly from the\n\
 134 command line to load and run an ELF executable file; this is like executing\n\
 135 that file itself, but always uses this helper program from the file you\n\
 136 specified, instead of the helper program file specified in the executable\n\
 137 file you run.  This is mostly of use for maintainers to test new versions\n\
 138 of this helper program; chances are you did not intend to run this program.\n"
 139                               );
 140
 141           interpreter_name = _dl_argv[0];
 142           --_dl_argc;
 143           ++_dl_argv;
 144           l = _dl_map_object (NULL, _dl_argv[0], user_entry);
 145           phdr = l->l_phdr;
 146           phent = l->l_phnum;
 147           l->l_type = lt_executable;
 148           l->l_libname = (char *) "";
 149         }
 150       else
 151         {
 152           /* Create a link_map for the executable itself.
 153              This will be what dlopen on "" returns.  */
 154           l = _dl_new_object ((char *) "", "", lt_executable);
 155           l->l_phdr = phdr;
 156           l->l_phnum = phent;
 157           interpreter_name = 0;
 158         }
 159
 160       /* Scan the program header table for the dynamic section.  */
 161       for (ph = phdr; ph < &phdr[phent]; ++ph)
 162         switch (ph->p_type)
 163           {
 164           case PT_DYNAMIC:
 165             /* This tells us where to find the dynamic section,
 166                which tells us everything we need to do.  */
 167             l->l_ld = (void *) ph->p_vaddr;
 168             break;
 169           case PT_INTERP:
 170             /* This "interpreter segment" was used by the program loader to
 171                find the program interpreter, which is this program itself, the
 172                dynamic linker.  We note what name finds us, so that a future
 173                dlopen call or DT_NEEDED entry, for something that wants to link
 174                against the dynamic linker as a shared library, will know that
 175                the shared object is already loaded.  */
 176             interpreter_name = (void *) ph->p_vaddr;
 177             break;
 178           }
 179       assert (interpreter_name); /* How else did we get here?  */
 180
 181       /* Extract the contents of the dynamic section for easy access.  */
 182       elf_get_dynamic_info (l->l_ld, l->l_info);
 183       /* Set up our cache of pointers into the hash table.  */
 184       _dl_setup_hash (l);
 185
 186       if (l->l_info[DT_DEBUG])
 187         /* There is a DT_DEBUG entry in the dynamic section.  Fill it in
 188            with the run-time address of the r_debug structure, which we
 189            will set up later to communicate with the debugger.  */
 190         l->l_info[DT_DEBUG]->d_un.d_ptr = (Elf32_Addr) &dl_r_debug;
 191
 192       l = _dl_new_object ((char *) interpreter_name, interpreter_name,
 193                           lt_interpreter);
 194
 195       /* Now process all the DT_NEEDED entries and map in the objects.
 196          Each new link_map will go on the end of the chain, so we will
 197          come across it later in the loop to map in its dependencies.  */
 198       for (l = _dl_loaded; l; l = l->l_next)
 199         {
 200           if (l->l_info[DT_NEEDED])
 201             {
 202               const char *strtab
 203                 = (void *) l->l_addr + l->l_info[DT_STRTAB]->d_un.d_ptr;
 204               const Elf32_Dyn *d;
 205               for (d = l->l_ld; d->d_tag != DT_NULL; ++d)
 206                 if (d->d_tag == DT_NEEDED)
 207                   _dl_map_object (l, strtab + d->d_un.d_val, NULL);
 208             }
 209           l->l_deps_loaded = 1;
 210         }
 211
 212       l = _dl_loaded->l_next;
 213       assert (l->l_type == lt_interpreter);
 214       if (l->l_opencount == 0)
 215         {
 216           /* No DT_NEEDED entry referred to the interpreter object itself.
 217              Remove it from the maps we will use for symbol resolution.  */
 218           l->l_prev->l_next = l->l_next;
 219           if (l->l_next)
 220             l->l_next->l_prev = l->l_prev;
 221         }
 222
 223       lazy = _dl_secure || *(getenv ("LD_BIND_NOW") ?: "");
 224
 225       /* Now we have all the objects loaded.  Relocate them all.
 226          We do this in reverse order so that copy relocs of earlier
 227          objects overwrite the data written by later objects.  */
 228       l = _dl_loaded;
 229       while (l->l_next)
 230         l = l->l_next;
 231       do
 232         {
 233           _dl_relocate_object (l, lazy);
 234           l = l->l_prev;
 235         } while (l);
 236
 237       /* Tell the debugger where to find the map of loaded objects.  */
 238       dl_r_debug.r_version = 1  /* R_DEBUG_VERSION XXX */;
 239       dl_r_debug.r_map = _dl_loaded;
 240       dl_r_debug.r_brk = (Elf32_Addr) &_dl_r_debug_state;
 241     }
 242   const char *errstring;
 243   const char *errobj;
 244   int err;
 245
 246   err = _dl_catch_error (&errstring, &errobj, &doit);
 247   if (errstring)
 248     _dl_sysdep_fatal (_dl_argv[0] ?: "<program name unknown>",
 249                       ": error in loading shared libraries\n",
 250                       errobj ?: "", errobj ? ": " : "",
 251                       errstring, err ? ": " : NULL,
 252                       err ? strerror (err) : NULL, NULL);
 253
 254   /* Once we return, _dl_sysdep_start will invoke
 255      the DT_INIT functions and then *USER_ENTRY.  */
 256 }
 257
 258 /* This function exists solely to have a breakpoint set on it by the
 259    debugger.  */
 260 void
 261 _dl_r_debug_state (void)
 262 {
 263 }
 264 \f
 265 #ifndef NDEBUG
 266
 267 /* Define (weakly) our own assert failure function which doesn't use stdio.
 268    If we are linked into the user program (-ldl), the normal __assert_fail
 269    defn can override this one.  */
 270
 271 #include "../stdio/_itoa.h"
 272
 273 void
 274 __assert_fail (const char *assertion,
 275                const char *file, unsigned int line, const char *function)
 276 {
 277   char buf[64];
 278   buf[sizeof buf - 1] = '\0';
 279   _dl_sysdep_fatal ("BUG IN DYNAMIC LINKER ld.so: ",
 280                     file, ": ", _itoa (line, buf + sizeof buf - 1, 10, 0),
 281                     ": ", function ?: "", function ? ": " : "",
 282                     "Assertion `", assertion, "' failed!\n");
 283
 284 }
 285 weak_symbol (__assert_fail)
 286
 287 #endif