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