elf/rtld.c

   1 /* Run time dynamic linker.
   2 Copyright (C) 1995, 1996 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 #include "../stdio-common/_itoa.h"
  26
  27
  28 #ifdef RTLD_START
  29 RTLD_START
  30 #else
  31 #error "sysdeps/MACHINE/dl-machine.h fails to define RTLD_START"
  32 #endif
  33
  34 /* System-specific function to do initial startup for the dynamic linker.
  35    After this, file access calls and getenv must work.  This is responsible
  36    for setting _dl_secure if we need to be secure (e.g. setuid),
  37    and for setting _dl_argc and _dl_argv, and then calling _dl_main.  */
  38 extern Elf32_Addr _dl_sysdep_start (void **start_argptr,
  39                                     void (*dl_main) (const Elf32_Phdr *phdr,
  40                                                      Elf32_Word phent,
  41                                                      Elf32_Addr *user_entry));
  42 extern void _dl_sysdep_start_cleanup (void);
  43
  44 int _dl_secure;
  45 int _dl_argc;
  46 char **_dl_argv;
  47 const char *_dl_rpath;
  48
  49 struct r_debug dl_r_debug;
  50
  51 static void dl_main (const Elf32_Phdr *phdr,
  52                      Elf32_Word phent,
  53                      Elf32_Addr *user_entry);
  54
  55 static struct link_map rtld_map;
  56
  57 Elf32_Addr
  58 _dl_start (void *arg)
  59 {
  60   struct link_map bootstrap_map;
  61
  62   /* Figure out the run-time load address of the dynamic linker itself.  */
  63   bootstrap_map.l_addr = elf_machine_load_address ();
  64
  65   /* Read our own dynamic section and fill in the info array.
  66      Conveniently, the first element of the GOT contains the
  67      offset of _DYNAMIC relative to the run-time load address.  */
  68   bootstrap_map.l_ld = (void *) bootstrap_map.l_addr + *elf_machine_got ();
  69   elf_get_dynamic_info (bootstrap_map.l_ld, bootstrap_map.l_info);
  70
  71 #ifdef ELF_MACHINE_BEFORE_RTLD_RELOC
  72   ELF_MACHINE_BEFORE_RTLD_RELOC (bootstrap_map.l_info);
  73 #endif
  74
  75   /* Relocate ourselves so we can do normal function calls and
  76      data access using the global offset table.  */
  77
  78   /* We must initialize `l_type' to make sure it is not `lt_interpreter'.
  79      That is the type to describe us, but not during bootstrapping--it
  80      indicates to elf_machine_rel{,a} that we were already relocated during
  81      bootstrapping, so it must anti-perform each bootstrapping relocation
  82      before applying the final relocation when ld.so is linked in as
  83      normal a shared library.  */
  84   bootstrap_map.l_type = lt_library;
  85   ELF_DYNAMIC_RELOCATE (&bootstrap_map, 0, NULL);
  86
  87
  88   /* Now life is sane; we can call functions and access global data.
  89      Set up to use the operating system facilities, and find out from
  90      the operating system's program loader where to find the program
  91      header table in core.  */
  92
  93
  94   /* Transfer data about ourselves to the permanent link_map structure.  */
  95   rtld_map.l_addr = bootstrap_map.l_addr;
  96   rtld_map.l_ld = bootstrap_map.l_ld;
  97   memcpy (rtld_map.l_info, bootstrap_map.l_info, sizeof rtld_map.l_info);
  98   _dl_setup_hash (&rtld_map);
  99
 100   /* Cache the DT_RPATH stored in ld.so itself; this will be
 101      the default search path.  */
 102   _dl_rpath = (void *) (rtld_map.l_addr +
 103                         rtld_map.l_info[DT_STRTAB]->d_un.d_ptr +
 104                         rtld_map.l_info[DT_RPATH]->d_un.d_val);
 105
 106   /* Call the OS-dependent function to set up life so we can do things like
 107      file access.  It will call `dl_main' (below) to do all the real work
 108      of the dynamic linker, and then unwind our frame and run the user
 109      entry point on the same stack we entered on.  */
 110   return _dl_sysdep_start (&arg, &dl_main);
 111 }
 112
 113
 114 /* Now life is peachy; we can do all normal operations.
 115    On to the real work.  */
 116
 117 void _start (void);
 118
 119 unsigned int _dl_skip_args;     /* Nonzero if we were run directly.  */
 120
 121 static void
 122 dl_main (const Elf32_Phdr *phdr,
 123          Elf32_Word phent,
 124          Elf32_Addr *user_entry)
 125 {
 126   const Elf32_Phdr *ph;
 127   struct link_map *l, *last, *before_rtld;
 128   const char *interpreter_name;
 129   int lazy;
 130   int list_only = 0;
 131
 132   if (*user_entry == (Elf32_Addr) &_start)
 133     {
 134       /* Ho ho.  We are not the program interpreter!  We are the program
 135          itself!  This means someone ran ld.so as a command.  Well, that
 136          might be convenient to do sometimes.  We support it by
 137          interpreting the args like this:
 138
 139          ld.so PROGRAM ARGS...
 140
 141          The first argument is the name of a file containing an ELF
 142          executable we will load and run with the following arguments.
 143          To simplify life here, PROGRAM is searched for using the
 144          normal rules for shared objects, rather than $PATH or anything
 145          like that.  We just load it and use its entry point; we don't
 146          pay attention to its PT_INTERP command (we are the interpreter
 147          ourselves).  This is an easy way to test a new ld.so before
 148          installing it.  */
 149       if (_dl_argc < 2)
 150         _dl_sysdep_fatal ("\
 151 Usage: ld.so [--list] EXECUTABLE-FILE [ARGS-FOR-PROGRAM...]\n\
 152 You have invoked `ld.so', the helper program for shared library executables.\n\
 153 This program usually lives in the file `/lib/ld.so', and special directives\n\
 154 in executable files using ELF shared libraries tell the system's program\n\
 155 loader to load the helper program from this file.  This helper program loads\n\
 156 the shared libraries needed by the program executable, prepares the program\n\
 157 to run, and runs it.  You may invoke this helper program directly from the\n\
 158 command line to load and run an ELF executable file; this is like executing\n\
 159 that file itself, but always uses this helper program from the file you\n\
 160 specified, instead of the helper program file specified in the executable\n\
 161 file you run.  This is mostly of use for maintainers to test new versions\n\
 162 of this helper program; chances are you did not intend to run this program.\n",
 163                           NULL);
 164
 165       interpreter_name = _dl_argv[0];
 166
 167       if (! strcmp (_dl_argv[1], "--list"))
 168         {
 169           list_only = 1;
 170
 171           ++_dl_skip_args;
 172           --_dl_argc;
 173           ++_dl_argv;
 174         }
 175
 176       ++_dl_skip_args;
 177       --_dl_argc;
 178       ++_dl_argv;
 179
 180       l = _dl_map_object (NULL, _dl_argv[0]);
 181       phdr = l->l_phdr;
 182       phent = l->l_phnum;
 183       l->l_name = (char *) "";
 184       *user_entry = l->l_entry;
 185     }
 186   else
 187     {
 188       /* Create a link_map for the executable itself.
 189          This will be what dlopen on "" returns.  */
 190       l = _dl_new_object ((char *) "", "", lt_executable);
 191       l->l_phdr = phdr;
 192       l->l_phnum = phent;
 193       interpreter_name = 0;
 194       l->l_entry = *user_entry;
 195     }
 196
 197   if (l != _dl_loaded)
 198     {
 199       /* GDB assumes that the first element on the chain is the
 200          link_map for the executable itself, and always skips it.
 201          Make sure the first one is indeed that one.  */
 202       l->l_prev->l_next = l->l_next;
 203       if (l->l_next)
 204         l->l_next->l_prev = l->l_prev;
 205       l->l_prev = NULL;
 206       l->l_next = _dl_loaded;
 207       _dl_loaded->l_prev = l;
 208       _dl_loaded = l;
 209     }
 210
 211   /* Scan the program header table for the dynamic section.  */
 212   for (ph = phdr; ph < &phdr[phent]; ++ph)
 213     switch (ph->p_type)
 214       {
 215       case PT_DYNAMIC:
 216         /* This tells us where to find the dynamic section,
 217            which tells us everything we need to do.  */
 218         l->l_ld = (void *) l->l_addr + ph->p_vaddr;
 219         break;
 220       case PT_INTERP:
 221         /* This "interpreter segment" was used by the program loader to
 222            find the program interpreter, which is this program itself, the
 223            dynamic linker.  We note what name finds us, so that a future
 224            dlopen call or DT_NEEDED entry, for something that wants to link
 225            against the dynamic linker as a shared library, will know that
 226            the shared object is already loaded.  */
 227         interpreter_name = (void *) l->l_addr + ph->p_vaddr;
 228         break;
 229       }
 230   assert (interpreter_name);    /* How else did we get here?  */
 231
 232   /* Extract the contents of the dynamic section for easy access.  */
 233   elf_get_dynamic_info (l->l_ld, l->l_info);
 234   if (l->l_info[DT_HASH])
 235     /* Set up our cache of pointers into the hash table.  */
 236     _dl_setup_hash (l);
 237
 238   if (l->l_info[DT_DEBUG])
 239     /* There is a DT_DEBUG entry in the dynamic section.  Fill it in
 240        with the run-time address of the r_debug structure, which we
 241        will set up later to communicate with the debugger.  */
 242     l->l_info[DT_DEBUG]->d_un.d_ptr = (Elf32_Addr) &dl_r_debug;
 243
 244   /* Put the link_map for ourselves on the chain so it can be found by
 245      name.  */
 246   rtld_map.l_name = (char *) rtld_map.l_libname = interpreter_name;
 247   rtld_map.l_type = lt_interpreter;
 248   while (l->l_next)
 249     l = l->l_next;
 250   l->l_next = &rtld_map;
 251   rtld_map.l_prev = l;
 252
 253   /* Now process all the DT_NEEDED entries and map in the objects.
 254      Each new link_map will go on the end of the chain, so we will
 255      come across it later in the loop to map in its dependencies.  */
 256   before_rtld = NULL;
 257   for (l = _dl_loaded; l; l = l->l_next)
 258     {
 259       if (l->l_info[DT_NEEDED])
 260         {
 261           const char *strtab
 262             = (void *) l->l_addr + l->l_info[DT_STRTAB]->d_un.d_ptr;
 263           const Elf32_Dyn *d;
 264           last = l;
 265           for (d = l->l_ld; d->d_tag != DT_NULL; ++d)
 266             if (d->d_tag == DT_NEEDED)
 267               {
 268                 struct link_map *new;
 269                 new = _dl_map_object (l, strtab + d->d_un.d_val);
 270                 if (!before_rtld && new == &rtld_map)
 271                   before_rtld = last;
 272                 last = new;
 273               }
 274         }
 275       l->l_deps_loaded = 1;
 276     }
 277
 278   /* If any DT_NEEDED entry referred to the interpreter object itself,
 279      reorder the list so it appears after its dependent.  If not,
 280      remove it from the maps we will use for symbol resolution.  */
 281   rtld_map.l_prev->l_next = rtld_map.l_next;
 282   if (rtld_map.l_next)
 283     rtld_map.l_next->l_prev = rtld_map.l_prev;
 284   if (before_rtld)
 285     {
 286       rtld_map.l_prev = before_rtld;
 287       rtld_map.l_next = before_rtld->l_next;
 288       before_rtld->l_next = &rtld_map;
 289       if (rtld_map.l_next)
 290         rtld_map.l_next->l_prev = &rtld_map;
 291     }
 292
 293   if (list_only)
 294     {
 295       /* We were run just to list the shared libraries.  It is
 296          important that we do this before real relocation, because the
 297          functions we call below for output may no longer work properly
 298          after relocation.  */
 299
 300       int i;
 301
 302       if (! _dl_loaded->l_info[DT_NEEDED])
 303         _dl_sysdep_message ("\t", "statically linked\n", NULL);
 304       else
 305         for (l = _dl_loaded->l_next; l; l = l->l_next)
 306           {
 307             char buf[20], *bp;
 308             buf[sizeof buf - 1] = '\0';
 309             bp = _itoa (l->l_addr, &buf[sizeof buf - 1], 16, 0);
 310             while (&buf[sizeof buf - 1] - bp < sizeof l->l_addr * 2)
 311               *--bp = '0';
 312             _dl_sysdep_message ("\t", l->l_libname, " => ", l->l_name,
 313                                 " (0x", bp, ")\n", NULL);
 314           }
 315
 316       for (i = 1; i < _dl_argc; ++i)
 317         {
 318           const Elf32_Sym *ref = NULL;
 319           Elf32_Addr loadbase = _dl_lookup_symbol (_dl_argv[i], &ref,
 320                                                    _dl_loaded, "argument",
 321                                                    0, 0);
 322           char buf[20], *bp;
 323           buf[sizeof buf - 1] = '\0';
 324           bp = _itoa (ref->st_value, &buf[sizeof buf - 1], 16, 0);
 325           while (&buf[sizeof buf - 1] - bp < sizeof loadbase * 2)
 326             *--bp = '0';
 327           _dl_sysdep_message (_dl_argv[i], " found at 0x", bp, NULL);
 328           buf[sizeof buf - 1] = '\0';
 329           bp = _itoa (loadbase, &buf[sizeof buf - 1], 16, 0);
 330           while (&buf[sizeof buf - 1] - bp < sizeof loadbase * 2)
 331             *--bp = '0';
 332           _dl_sysdep_message (" in object at 0x", bp, "\n", NULL);
 333         }
 334
 335       _exit (0);
 336     }
 337
 338   lazy = !_dl_secure && *(getenv ("LD_BIND_NOW") ?: "") == '\0';
 339
 340   /* Now we have all the objects loaded.  Relocate them all except for
 341      the dynamic linker itself.  We do this in reverse order so that
 342      copy relocs of earlier objects overwrite the data written by later
 343      objects.  We do not re-relocate the dynamic linker itself in this
 344      loop because that could result in the GOT entries for functions we
 345      call being changed, and that would break us.  It is safe to
 346      relocate the dynamic linker out of order because it has no copy
 347      relocs (we know that because it is self-contained).  */
 348   l = _dl_loaded;
 349   while (l->l_next)
 350     l = l->l_next;
 351   do
 352     {
 353       if (l != &rtld_map)
 354         _dl_relocate_object (l, lazy);
 355       l = l->l_prev;
 356     } while (l);
 357
 358   /* Do any necessary cleanups for the startup OS interface code.
 359      We do these now so that no calls are made after rtld re-relocation
 360      which might be resolved to different functions than we expect.
 361      We cannot do this before relocating the other objects because
 362      _dl_relocate_object might need to call `mprotect' for DT_TEXTREL.  */
 363   _dl_sysdep_start_cleanup ();
 364
 365   if (rtld_map.l_opencount > 0)
 366     /* There was an explicit ref to the dynamic linker as a shared lib.
 367        Re-relocate ourselves with user-controlled symbol definitions.  */
 368     _dl_relocate_object (&rtld_map, lazy);
 369
 370   /* Tell the debugger where to find the map of loaded objects.  */
 371   dl_r_debug.r_version = 1      /* R_DEBUG_VERSION XXX */;
 372   dl_r_debug.r_ldbase = rtld_map.l_addr; /* Record our load address.  */
 373   dl_r_debug.r_map = _dl_loaded;
 374   dl_r_debug.r_brk = (Elf32_Addr) &_dl_r_debug_state;
 375
 376   if (rtld_map.l_info[DT_INIT])
 377     {
 378       /* Call the initializer for the compatibility version of the
 379          dynamic linker.  There is no additional initialization
 380          required for the ABI-compliant dynamic linker.  */
 381
 382       (*(void (*) (void)) (rtld_map.l_addr +
 383                            rtld_map.l_info[DT_INIT]->d_un.d_ptr)) ();
 384
 385       /* Clear the field so a future dlopen won't run it again.  */
 386       rtld_map.l_info[DT_INIT] = NULL;
 387     }
 388
 389   /* Once we return, _dl_sysdep_start will invoke
 390      the DT_INIT functions and then *USER_ENTRY.  */
 391 }
 392
 393 /* This function exists solely to have a breakpoint set on it by the
 394    debugger.  */
 395 void
 396 _dl_r_debug_state (void)
 397 {
 398 }