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 struct link_map _dl_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   _dl_rtld_map.l_addr = bootstrap_map.l_addr;
  96   _dl_rtld_map.l_ld = bootstrap_map.l_ld;
  97   memcpy (_dl_rtld_map.l_info, bootstrap_map.l_info,
  98           sizeof _dl_rtld_map.l_info);
  99   _dl_setup_hash (&_dl_rtld_map);
 100
 101   /* Cache the DT_RPATH stored in ld.so itself; this will be
 102      the default search path.  */
 103   _dl_rpath = (void *) (_dl_rtld_map.l_addr +
 104                         _dl_rtld_map.l_info[DT_STRTAB]->d_un.d_ptr +
 105                         _dl_rtld_map.l_info[DT_RPATH]->d_un.d_val);
 106
 107   /* Call the OS-dependent function to set up life so we can do things like
 108      file access.  It will call `dl_main' (below) to do all the real work
 109      of the dynamic linker, and then unwind our frame and run the user
 110      entry point on the same stack we entered on.  */
 111   return _dl_sysdep_start (&arg, &dl_main);
 112 }
 113
 114
 115 /* Now life is peachy; we can do all normal operations.
 116    On to the real work.  */
 117
 118 void _start (void);
 119
 120 unsigned int _dl_skip_args;     /* Nonzero if we were run directly.  */
 121
 122 static void
 123 dl_main (const Elf32_Phdr *phdr,
 124          Elf32_Word phent,
 125          Elf32_Addr *user_entry)
 126 {
 127   const Elf32_Phdr *ph;
 128   struct link_map *l;
 129   const char *interpreter_name;
 130   int lazy;
 131   int list_only = 0;
 132
 133   if (*user_entry == (Elf32_Addr) &_start)
 134     {
 135       /* Ho ho.  We are not the program interpreter!  We are the program
 136          itself!  This means someone ran ld.so as a command.  Well, that
 137          might be convenient to do sometimes.  We support it by
 138          interpreting the args like this:
 139
 140          ld.so PROGRAM ARGS...
 141
 142          The first argument is the name of a file containing an ELF
 143          executable we will load and run with the following arguments.
 144          To simplify life here, PROGRAM is searched for using the
 145          normal rules for shared objects, rather than $PATH or anything
 146          like that.  We just load it and use its entry point; we don't
 147          pay attention to its PT_INTERP command (we are the interpreter
 148          ourselves).  This is an easy way to test a new ld.so before
 149          installing it.  */
 150       if (_dl_argc < 2)
 151         _dl_sysdep_fatal ("\
 152 Usage: ld.so [--list] EXECUTABLE-FILE [ARGS-FOR-PROGRAM...]\n\
 153 You have invoked `ld.so', the helper program for shared library executables.\n\
 154 This program usually lives in the file `/lib/ld.so', and special directives\n\
 155 in executable files using ELF shared libraries tell the system's program\n\
 156 loader to load the helper program from this file.  This helper program loads\n\
 157 the shared libraries needed by the program executable, prepares the program\n\
 158 to run, and runs it.  You may invoke this helper program directly from the\n\
 159 command line to load and run an ELF executable file; this is like executing\n\
 160 that file itself, but always uses this helper program from the file you\n\
 161 specified, instead of the helper program file specified in the executable\n\
 162 file you run.  This is mostly of use for maintainers to test new versions\n\
 163 of this helper program; chances are you did not intend to run this program.\n",
 164                           NULL);
 165
 166       interpreter_name = _dl_argv[0];
 167
 168       if (! strcmp (_dl_argv[1], "--list"))
 169         {
 170           list_only = 1;
 171
 172           ++_dl_skip_args;
 173           --_dl_argc;
 174           ++_dl_argv;
 175         }
 176
 177       ++_dl_skip_args;
 178       --_dl_argc;
 179       ++_dl_argv;
 180
 181       l = _dl_map_object (NULL, _dl_argv[0]);
 182       phdr = l->l_phdr;
 183       phent = l->l_phnum;
 184       l->l_name = (char *) "";
 185       *user_entry = l->l_entry;
 186     }
 187   else
 188     {
 189       /* Create a link_map for the executable itself.
 190          This will be what dlopen on "" returns.  */
 191       l = _dl_new_object ((char *) "", "", lt_executable);
 192       l->l_phdr = phdr;
 193       l->l_phnum = phent;
 194       interpreter_name = 0;
 195       l->l_entry = *user_entry;
 196     }
 197
 198   if (l != _dl_loaded)
 199     {
 200       /* GDB assumes that the first element on the chain is the
 201          link_map for the executable itself, and always skips it.
 202          Make sure the first one is indeed that one.  */
 203       l->l_prev->l_next = l->l_next;
 204       if (l->l_next)
 205         l->l_next->l_prev = l->l_prev;
 206       l->l_prev = NULL;
 207       l->l_next = _dl_loaded;
 208       _dl_loaded->l_prev = l;
 209       _dl_loaded = l;
 210     }
 211
 212   /* Scan the program header table for the dynamic section.  */
 213   for (ph = phdr; ph < &phdr[phent]; ++ph)
 214     switch (ph->p_type)
 215       {
 216       case PT_DYNAMIC:
 217         /* This tells us where to find the dynamic section,
 218            which tells us everything we need to do.  */
 219         l->l_ld = (void *) l->l_addr + ph->p_vaddr;
 220         break;
 221       case PT_INTERP:
 222         /* This "interpreter segment" was used by the program loader to
 223            find the program interpreter, which is this program itself, the
 224            dynamic linker.  We note what name finds us, so that a future
 225            dlopen call or DT_NEEDED entry, for something that wants to link
 226            against the dynamic linker as a shared library, will know that
 227            the shared object is already loaded.  */
 228         interpreter_name = (void *) l->l_addr + ph->p_vaddr;
 229         break;
 230       }
 231   assert (interpreter_name);    /* How else did we get here?  */
 232
 233   /* Extract the contents of the dynamic section for easy access.  */
 234   elf_get_dynamic_info (l->l_ld, l->l_info);
 235   if (l->l_info[DT_HASH])
 236     /* Set up our cache of pointers into the hash table.  */
 237     _dl_setup_hash (l);
 238
 239   if (l->l_info[DT_DEBUG])
 240     /* There is a DT_DEBUG entry in the dynamic section.  Fill it in
 241        with the run-time address of the r_debug structure, which we
 242        will set up later to communicate with the debugger.  */
 243     l->l_info[DT_DEBUG]->d_un.d_ptr = (Elf32_Addr) &dl_r_debug;
 244
 245   /* Put the link_map for ourselves on the chain so it can be found by
 246      name.  */
 247   _dl_rtld_map.l_name = (char *) _dl_rtld_map.l_libname = interpreter_name;
 248   _dl_rtld_map.l_type = lt_interpreter;
 249   while (l->l_next)
 250     l = l->l_next;
 251   l->l_next = &_dl_rtld_map;
 252   _dl_rtld_map.l_prev = l;
 253
 254   /* Load all the libraries specified by DT_NEEDED entries.  */
 255   _dl_map_object_deps (l);
 256
 257   /* XXX if kept, move it so l_next list is in dep order because
 258      it will determine gdb's search order.
 259      Perhaps do this always, so later dlopen by name finds it?
 260      XXX But then gdb always considers it present.  */
 261   if (_dl_rtld_map.l_opencount == 0)
 262     {
 263       /* No DT_NEEDED entry referred to the interpreter object itself,
 264          so remove it from the list of visible objects.  */
 265       _dl_rtld_map.l_prev->l_next = _dl_rtld_map.l_next;
 266       _dl_rtld_map.l_next->l_prev = _dl_rtld_map.l_prev;
 267     }
 268
 269   if (list_only)
 270     {
 271       /* We were run just to list the shared libraries.  It is
 272          important that we do this before real relocation, because the
 273          functions we call below for output may no longer work properly
 274          after relocation.  */
 275
 276       int i;
 277
 278       if (! _dl_loaded->l_info[DT_NEEDED])
 279         _dl_sysdep_message ("\t", "statically linked\n", NULL);
 280       else
 281         for (l = _dl_loaded->l_next; l; l = l->l_next)
 282           {
 283             char buf[20], *bp;
 284             buf[sizeof buf - 1] = '\0';
 285             bp = _itoa (l->l_addr, &buf[sizeof buf - 1], 16, 0);
 286             while (&buf[sizeof buf - 1] - bp < sizeof l->l_addr * 2)
 287               *--bp = '0';
 288             _dl_sysdep_message ("\t", l->l_libname, " => ", l->l_name,
 289                                 " (0x", bp, ")\n", NULL);
 290           }
 291
 292       for (i = 1; i < _dl_argc; ++i)
 293         {
 294           const Elf32_Sym *ref = NULL;
 295           struct link_map *scope[2] ={ _dl_loaded, NULL };
 296           Elf32_Addr loadbase
 297             = _dl_lookup_symbol (_dl_argv[i], &ref, scope, "argument", 0, 0);
 298           char buf[20], *bp;
 299           buf[sizeof buf - 1] = '\0';
 300           bp = _itoa (ref->st_value, &buf[sizeof buf - 1], 16, 0);
 301           while (&buf[sizeof buf - 1] - bp < sizeof loadbase * 2)
 302             *--bp = '0';
 303           _dl_sysdep_message (_dl_argv[i], " found at 0x", bp, NULL);
 304           buf[sizeof buf - 1] = '\0';
 305           bp = _itoa (loadbase, &buf[sizeof buf - 1], 16, 0);
 306           while (&buf[sizeof buf - 1] - bp < sizeof loadbase * 2)
 307             *--bp = '0';
 308           _dl_sysdep_message (" in object at 0x", bp, "\n", NULL);
 309         }
 310
 311       _exit (0);
 312     }
 313
 314   lazy = !_dl_secure && *(getenv ("LD_BIND_NOW") ?: "") == '\0';
 315
 316   /* Now we have all the objects loaded.  Relocate them all except for
 317      the dynamic linker itself.  We do this in reverse order so that
 318      copy relocs of earlier objects overwrite the data written by later
 319      objects.  We do not re-relocate the dynamic linker itself in this
 320      loop because that could result in the GOT entries for functions we
 321      call being changed, and that would break us.  It is safe to
 322      relocate the dynamic linker out of order because it has no copy
 323      relocs (we know that because it is self-contained).  */
 324   l = _dl_loaded;
 325   while (l->l_next)
 326     l = l->l_next;
 327   do
 328     {
 329       if (l != &_dl_rtld_map)
 330         _dl_relocate_object (l, lazy);
 331       l = l->l_prev;
 332     } while (l);
 333
 334   /* Do any necessary cleanups for the startup OS interface code.
 335      We do these now so that no calls are made after rtld re-relocation
 336      which might be resolved to different functions than we expect.
 337      We cannot do this before relocating the other objects because
 338      _dl_relocate_object might need to call `mprotect' for DT_TEXTREL.  */
 339   _dl_sysdep_start_cleanup ();
 340
 341   if (_dl_rtld_map.l_opencount > 0)
 342     /* There was an explicit ref to the dynamic linker as a shared lib.
 343        Re-relocate ourselves with user-controlled symbol definitions.  */
 344     _dl_relocate_object (&_dl_rtld_map, lazy);
 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 = (Elf32_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 }