glibc/sysdeps/generic/dl-cache.c

/* Support for reading /etc/ld.so.cache files written by Linux ldconfig.
   Copyright (C) 1996, 1997 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 <link.h>
#include <stddef.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];
  };

/* 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)
{
  static struct cache_file *cache;
  static size_t cachesize;
  unsigned int i;
  const char *best;

  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)))
      {
	best = ((const char *) &cache->libs[cache->nlibs]
		+ cache->libs[i].value);

	if (cache->libs[i].flags == 3)
	  /* We've found an exact match for the shared object and no
	     general `ELF' release.  Stop searching.  */
	  break;
      }
  return best;
}