glibc/sysdeps/generic/dl-cache.c

/* Support for reading /etc/ld.so.cache files written by Linux ldconfig.
   Copyright (C) 1996, 1997, 1998 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., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#include <unistd.h>
#include <elf/ldsodefs.h>
#include <sys/mman.h>

/* System-dependent function to read a file's whole contents
   in the most convenient manner available.  */
extern void *_dl_sysdep_read_whole_file (const char *filename,
					 size_t *filesize_ptr,
					 int mmap_prot);

#ifndef LD_SO_CACHE
# define LD_SO_CACHE "/etc/ld.so.cache"
#endif

#define CACHEMAGIC "ld.so-1.7.0"

struct cache_file
  {
    char magic[sizeof CACHEMAGIC - 1];
    unsigned int nlibs;
    struct
      {
	int flags;		/* This is 1 for an ELF library.  */
	unsigned int key, value; /* String table indices.  */
      } libs[0];
  };

/* This is the starting address and the size of the mmap()ed file.  */
static struct cache_file *cache;
static size_t cachesize;

/* This is the cache ID we expect.  Normally it is 3 for glibc linked
   binaries.  */
int _dl_correct_cache_id = 3;

/* Look up NAME in ld.so.cache and return the file name stored there,
   or null if none is found.  */

const char *
_dl_load_cache_lookup (const char *name)
{
  unsigned int i;
  const char *best;

  /* Print a message if the loading of libs is traced.  */
  if (_dl_debug_libs)
    _dl_debug_message (1, " search cache=", LD_SO_CACHE, "\n", NULL);

  if (cache == NULL)
    {
      /* Read the contents of the file.  */
      void *file = _dl_sysdep_read_whole_file (LD_SO_CACHE, &cachesize,
					       PROT_READ);
      if (file && cachesize > sizeof *cache &&
	  !memcmp (file, CACHEMAGIC, sizeof CACHEMAGIC - 1))
	/* Looks ok.  */
	cache = file;
      else
	{
	  if (file)
	    __munmap (file, cachesize);
	  cache = (void *) -1;
	  return NULL;
	}
    }

  if (cache == (void *) -1)
    /* Previously looked for the cache file and didn't find it.  */
    return NULL;

  best = NULL;
  for (i = 0; i < cache->nlibs; ++i)
    if ((cache->libs[i].flags == 1 ||
	 cache->libs[i].flags == 3) && /* ELF library entry.  */
	/* Make sure string table indices are not bogus before using them.  */
	cache->libs[i].key < cachesize - sizeof *cache &&
	cache->libs[i].value < cachesize - sizeof *cache &&
	/* Does the name match?  */
	! strcmp (name, ((const char *) &cache->libs[cache->nlibs] +
			 cache->libs[i].key)))
      {
	if ((best == NULL) || (cache->libs[i].flags == _dl_correct_cache_id))
	  {
	    best = ((const char *) &cache->libs[cache->nlibs]
		    + cache->libs[i].value);

	    if (cache->libs[i].flags == _dl_correct_cache_id)
	      /* We've found an exact match for the shared object and no
		 general `ELF' release.  Stop searching.  */
	      break;
	  }
      }

  /* Print our result if wanted.  */
  if (_dl_debug_libs && best != NULL)
    _dl_debug_message (1, "  trying file=", best, "\n", NULL);

  return best;
}

#ifndef MAP_COPY
/* If the system does not support MAP_COPY we cannot leave the file open
   all the time since this would create problems when the file is replaced.
   Therefore we provide this function to close the file and open it again
   once needed.  */
void
_dl_unload_cache (void)
{
  if (cache != NULL && cache != (struct cache_file *) -1)
    {
      __munmap (cache, cachesize);
      cache = NULL;
    }
}
#endif