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   /* We must initialize `l_type' to make sure it is not `lt_interpreter'.
  74      That is the type to describe us, but not during bootstrapping--it
  75      indicates to elf_machine_rel{,a} that we were already relocated during
  76      bootstrapping, so it must anti-perform each bootstrapping relocation
  77      before applying the final relocation when ld.so is linked in as
  78      normal a shared library.  */
  79   rtld_map.l_type = lt_library;
  80   ELF_DYNAMIC_RELOCATE (&rtld_map, 0, NULL);
  81
  82
  83   /* Now life is sane; we can call functions and access global data.
  84      Set up to use the operating system facilities, and find out from
  85      the operating system's program loader where to find the program
  86      header table in core.  */
  87
  88   dl_r_debug.r_ldbase = rtld_map.l_addr; /* Record our load address.  */
  89
  90   /* Call the OS-dependent function to set up life so we can do things like
  91      file access.  It will call `dl_main' (below) to do all the real work
  92      of the dynamic linker, and then unwind our frame and run the user
  93      entry point on the same stack we entered on.  */
  94   return _dl_sysdep_start (&arg, &dl_main);
  95 }
  96
  97
  98 /* Now life is peachy; we can do all normal operations.
  99    On to the real work.  */
 100
 101 void _start (void);
 102
 103 static int rtld_command;        /* Nonzero if we were run directly.  */
 104
 105 static void
 106 dl_main (const Elf32_Phdr *phdr,
 107          Elf32_Word phent,
 108          Elf32_Addr *user_entry)
 109 {
 110   void doit (void)
 111     {
 112       const Elf32_Phdr *ph;
 113       struct link_map *l;
 114       const char *interpreter_name;
 115       int lazy;
 116
 117       if (*user_entry == (Elf32_Addr) &_start)
 118         {
 119           /* Ho ho.  We are not the program interpreter!  We are the program
 120              itself!  This means someone ran ld.so as a command.  Well, that
 121              might be convenient to do sometimes.  We support it by
 122              interpreting the args like this:
 123
 124              ld.so PROGRAM ARGS...
 125
 126              The first argument is the name of a file containing an ELF
 127              executable we will load and run with the following arguments.
 128              To simplify life here, PROGRAM is searched for using the
 129              normal rules for shared objects, rather than $PATH or anything
 130              like that.  We just load it and use its entry point; we don't
 131              pay attention to its PT_INTERP command (we are the interpreter
 132              ourselves).  This is an easy way to test a new ld.so before
 133              installing it.  */
 134           if (_dl_argc < 2)
 135             _dl_sysdep_fatal ("\
 136 Usage: ld.so EXECUTABLE-FILE [ARGS-FOR-PROGRAM...]\n\
 137 You have invoked `ld.so', the helper program for shared library executables.\n\
 138 This program usually lives in the file `/lib/ld.so', and special directives\n\
 139 in executable files using ELF shared libraries tell the system's program\n\
 140 loader to load the helper program from this file.  This helper program loads\n\
 141 the shared libraries needed by the program executable, prepares the program\n\
 142 to run, and runs it.  You may invoke this helper program directly from the\n\
 143 command line to load and run an ELF executable file; this is like executing\n\
 144 that file itself, but always uses this helper program from the file you\n\
 145 specified, instead of the helper program file specified in the executable\n\
 146 file you run.  This is mostly of use for maintainers to test new versions\n\
 147 of this helper program; chances are you did not intend to run this program.\n",
 148                               NULL);
 149
 150           rtld_command = 1;
 151           interpreter_name = _dl_argv[0];
 152           --_dl_argc;
 153           ++_dl_argv;
 154           l = _dl_map_object (NULL, _dl_argv[0], user_entry);
 155           phdr = l->l_phdr;
 156           phent = l->l_phnum;
 157           l->l_type = lt_executable;
 158           l->l_libname = (char *) "";
 159         }
 160       else
 161         {
 162           /* Create a link_map for the executable itself.
 163              This will be what dlopen on "" returns.  */
 164           l = _dl_new_object ((char *) "", "", lt_executable);
 165           l->l_phdr = phdr;
 166           l->l_phnum = phent;
 167           interpreter_name = 0;
 168         }
 169
 170       /* Scan the program header table for the dynamic section.  */
 171       for (ph = phdr; ph < &phdr[phent]; ++ph)
 172         switch (ph->p_type)
 173           {
 174           case PT_DYNAMIC:
 175             /* This tells us where to find the dynamic section,
 176                which tells us everything we need to do.  */
 177             l->l_ld = (void *) l->l_addr + ph->p_vaddr;
 178             break;
 179           case PT_INTERP:
 180             /* This "interpreter segment" was used by the program loader to
 181                find the program interpreter, which is this program itself, the
 182                dynamic linker.  We note what name finds us, so that a future
 183                dlopen call or DT_NEEDED entry, for something that wants to link
 184                against the dynamic linker as a shared library, will know that
 185                the shared object is already loaded.  */
 186             interpreter_name = (void *) l->l_addr + ph->p_vaddr;
 187             break;
 188           }
 189       assert (interpreter_name); /* How else did we get here?  */
 190
 191       /* Extract the contents of the dynamic section for easy access.  */
 192       elf_get_dynamic_info (l->l_ld, l->l_info);
 193       /* Set up our cache of pointers into the hash table.  */
 194       _dl_setup_hash (l);
 195
 196       if (l->l_info[DT_DEBUG])
 197         /* There is a DT_DEBUG entry in the dynamic section.  Fill it in
 198            with the run-time address of the r_debug structure, which we
 199            will set up later to communicate with the debugger.  */
 200         l->l_info[DT_DEBUG]->d_un.d_ptr = (Elf32_Addr) &dl_r_debug;
 201
 202       l = _dl_new_object ((char *) interpreter_name, interpreter_name,
 203                           lt_interpreter);
 204
 205       /* Now process all the DT_NEEDED entries and map in the objects.
 206          Each new link_map will go on the end of the chain, so we will
 207          come across it later in the loop to map in its dependencies.  */
 208       for (l = _dl_loaded; l; l = l->l_next)
 209         {
 210           if (l->l_info[DT_NEEDED])
 211             {
 212               const char *strtab
 213                 = (void *) l->l_addr + l->l_info[DT_STRTAB]->d_un.d_ptr;
 214               const Elf32_Dyn *d;
 215               for (d = l->l_ld; d->d_tag != DT_NULL; ++d)
 216                 if (d->d_tag == DT_NEEDED)
 217                   _dl_map_object (l, strtab + d->d_un.d_val, NULL);
 218             }
 219           l->l_deps_loaded = 1;
 220         }
 221
 222       l = _dl_loaded->l_next;
 223       assert (l->l_type == lt_interpreter);
 224       if (l->l_opencount == 0)
 225         {
 226           /* No DT_NEEDED entry referred to the interpreter object itself.
 227              Remove it from the maps we will use for symbol resolution.  */
 228           l->l_prev->l_next = l->l_next;
 229           if (l->l_next)
 230             l->l_next->l_prev = l->l_prev;
 231         }
 232
 233       lazy = !_dl_secure && *(getenv ("LD_BIND_NOW") ?: "") == '\0';
 234
 235       /* Now we have all the objects loaded.  Relocate them all.
 236          We do this in reverse order so that copy relocs of earlier
 237          objects overwrite the data written by later objects.  */
 238       l = _dl_loaded;
 239       while (l->l_next)
 240         l = l->l_next;
 241       do
 242         {
 243           _dl_relocate_object (l, lazy);
 244           l = l->l_prev;
 245         } while (l);
 246
 247       /* Tell the debugger where to find the map of loaded objects.  */
 248       dl_r_debug.r_version = 1  /* R_DEBUG_VERSION XXX */;
 249       dl_r_debug.r_map = _dl_loaded;
 250       dl_r_debug.r_brk = (Elf32_Addr) &_dl_r_debug_state;
 251     }
 252   const char *errstring;
 253   const char *errobj;
 254   int err;
 255
 256   err = _dl_catch_error (&errstring, &errobj, &doit);
 257   if (errstring)
 258     _dl_sysdep_fatal (_dl_argv[0] ?: "<program name unknown>",
 259                       ": error in loading shared libraries\n",
 260                       errobj ?: "", errobj ? ": " : "",
 261                       errstring, err ? ": " : "",
 262                       err ? strerror (err) : "", "\n", NULL);
 263
 264   /* Once we return, _dl_sysdep_start will invoke
 265      the DT_INIT functions and then *USER_ENTRY.  */
 266 }
 267
 268 /* This function exists solely to have a breakpoint set on it by the
 269    debugger.  */
 270 void
 271 _dl_r_debug_state (void)
 272 {
 273 }
 274 \f
 275 #ifndef NDEBUG
 276
 277 /* Define (weakly) our own assert failure function which doesn't use stdio.
 278    If we are linked into the user program (-ldl), the normal __assert_fail
 279    defn can override this one.  */
 280
 281 #include "../stdio/_itoa.h"
 282
 283 void
 284 __assert_fail (const char *assertion,
 285                const char *file, unsigned int line, const char *function)
 286 {
 287   char buf[64];
 288   buf[sizeof buf - 1] = '\0';
 289   _dl_sysdep_fatal ("BUG IN DYNAMIC LINKER ld.so: ",
 290                     file, ": ", _itoa (line, buf + sizeof buf - 1, 10, 0),
 291                     ": ", function ?: "", function ? ": " : "",
 292                     "Assertion `", assertion, "' failed!\n",
 293                     NULL);
 294
 295 }
 296 weak_symbol (__assert_fail)
 297
 298 void
 299 __assert_perror_fail (int errnum,
 300                       const char *file, unsigned int line,
 301                       const char *function)
 302 {
 303   char buf[64];
 304   buf[sizeof buf - 1] = '\0';
 305   _dl_sysdep_fatal ("BUG IN DYNAMIC LINKER ld.so: ",
 306                     file, ": ", _itoa (line, buf + sizeof buf - 1, 10, 0),
 307                     ": ", function ?: "", function ? ": " : "",
 308                     "Unexpected error: ", strerror (errnum), "\n", NULL);
 309
 310 }
 311 weak_symbol (__assert_perror_fail)
 312
 313 #endif