path: root/elf/rtld.c

/* Run time dynamic linker.
Copyright (C) 1995, 1996 Free Software Foundation, Inc.
This file is part of the GNU C Library.

The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.

The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Library General Public License for more details.

You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB.  If
not, write to the Free Software Foundation, Inc., 675 Mass Ave,
Cambridge, MA 02139, USA.  */

#include <link.h>
#include "dynamic-link.h"
#include <stddef.h>
#include <stdlib.h>
#include <unistd.h>
#include "../stdio-common/_itoa.h"


#ifdef RTLD_START
RTLD_START
#else
#error "sysdeps/MACHINE/dl-machine.h fails to define RTLD_START"
#endif

/* System-specific function to do initial startup for the dynamic linker.
   After this, file access calls and getenv must work.  This is responsible
   for setting _dl_secure if we need to be secure (e.g. setuid),
   and for setting _dl_argc and _dl_argv, and then calling _dl_main.  */
extern ElfW(Addr) _dl_sysdep_start (void **start_argptr,
				    void (*dl_main) (const ElfW(Phdr) *phdr,
						     ElfW(Half) phent,
						     ElfW(Addr) *user_entry));
extern void _dl_sysdep_start_cleanup (void);

int _dl_secure;
int _dl_argc;
char **_dl_argv;
const char *_dl_rpath;

static void dl_main (const ElfW(Phdr) *phdr,
		     ElfW(Half) phent,
		     ElfW(Addr) *user_entry);

struct link_map _dl_rtld_map;

ElfW(Addr)
_dl_start (void *arg)
{
  struct link_map bootstrap_map;

  /* Figure out the run-time load address of the dynamic linker itself.  */
  bootstrap_map.l_addr = elf_machine_load_address ();

  /* Read our own dynamic section and fill in the info array.
     Conveniently, the first element of the GOT contains the
     offset of _DYNAMIC relative to the run-time load address.  */
  bootstrap_map.l_ld = (void *) bootstrap_map.l_addr + *elf_machine_got ();
  elf_get_dynamic_info (bootstrap_map.l_ld, bootstrap_map.l_info);

#ifdef ELF_MACHINE_BEFORE_RTLD_RELOC
  ELF_MACHINE_BEFORE_RTLD_RELOC (bootstrap_map.l_info);
#endif

  /* Relocate ourselves so we can do normal function calls and
     data access using the global offset table.  */

  ELF_DYNAMIC_RELOCATE (&bootstrap_map, 0, NULL);


  /* Now life is sane; we can call functions and access global data.
     Set up to use the operating system facilities, and find out from
     the operating system's program loader where to find the program
     header table in core.  */


  /* Transfer data about ourselves to the permanent link_map structure.  */
  _dl_rtld_map.l_addr = bootstrap_map.l_addr;
  _dl_rtld_map.l_ld = bootstrap_map.l_ld;
  memcpy (_dl_rtld_map.l_info, bootstrap_map.l_info,
	  sizeof _dl_rtld_map.l_info);
  _dl_setup_hash (&_dl_rtld_map);

  /* Cache the DT_RPATH stored in ld.so itself; this will be
     the default search path.  */
  _dl_rpath = (void *) (_dl_rtld_map.l_addr +
			_dl_rtld_map.l_info[DT_STRTAB]->d_un.d_ptr +
			_dl_rtld_map.l_info[DT_RPATH]->d_un.d_val);

  /* Call the OS-dependent function to set up life so we can do things like
     file access.  It will call `dl_main' (below) to do all the real work
     of the dynamic linker, and then unwind our frame and run the user
     entry point on the same stack we entered on.  */
  return _dl_sysdep_start (arg, &dl_main);
}


/* Now life is peachy; we can do all normal operations.
   On to the real work.  */

void _start (void);

unsigned int _dl_skip_args;	/* Nonzero if we were run directly.  */

static void
dl_main (const ElfW(Phdr) *phdr,
	 ElfW(Half) phent,
	 ElfW(Addr) *user_entry)
{
  const ElfW(Phdr) *ph;
  struct link_map *l;
  const char *interpreter_name;
  int lazy;
  int list_only = 0;

  if (*user_entry == (ElfW(Addr)) &_start)
    {
      /* Ho ho.  We are not the program interpreter!  We are the program
	 itself!  This means someone ran ld.so as a command.  Well, that
	 might be convenient to do sometimes.  We support it by
	 interpreting the args like this:

	 ld.so PROGRAM ARGS...

	 The first argument is the name of a file containing an ELF
	 executable we will load and run with the following arguments.
	 To simplify life here, PROGRAM is searched for using the
	 normal rules for shared objects, rather than $PATH or anything
	 like that.  We just load it and use its entry point; we don't
	 pay attention to its PT_INTERP command (we are the interpreter
	 ourselves).  This is an easy way to test a new ld.so before
	 installing it.  */
      if (_dl_argc < 2)
	_dl_sysdep_fatal ("\
Usage: ld.so [--list] EXECUTABLE-FILE [ARGS-FOR-PROGRAM...]\n\
You have invoked `ld.so', the helper program for shared library executables.\n\
This program usually lives in the file `/lib/ld.so', and special directives\n\
in executable files using ELF shared libraries tell the system's program\n\
loader to load the helper program from this file.  This helper program loads\n\
the shared libraries needed by the program executable, prepares the program\n\
to run, and runs it.  You may invoke this helper program directly from the\n\
command line to load and run an ELF executable file; this is like executing\n\
that file itself, but always uses this helper program from the file you\n\
specified, instead of the helper program file specified in the executable\n\
file you run.  This is mostly of use for maintainers to test new versions\n\
of this helper program; chances are you did not intend to run this program.\n",
			  NULL);

      interpreter_name = _dl_argv[0];

      if (! strcmp (_dl_argv[1], "--list"))
	{
	  list_only = 1;

	  ++_dl_skip_args;
	  --_dl_argc;
	  ++_dl_argv;
	}

      ++_dl_skip_args;
      --_dl_argc;
      ++_dl_argv;

      l = _dl_map_object (NULL, _dl_argv[0], lt_library);
      phdr = l->l_phdr;
      phent = l->l_phnum;
      l->l_name = (char *) "";
      *user_entry = l->l_entry;
    }
  else
    {
      /* Create a link_map for the executable itself.
	 This will be what dlopen on "" returns.  */
      l = _dl_new_object ((char *) "", "", lt_library);
      l->l_phdr = phdr;
      l->l_phnum = phent;
      interpreter_name = 0;
      l->l_entry = *user_entry;
    }

  if (l != _dl_loaded)
    {
      /* GDB assumes that the first element on the chain is the
	 link_map for the executable itself, and always skips it.
	 Make sure the first one is indeed that one.  */
      l->l_prev->l_next = l->l_next;