glibc/sysdeps/generic/dl-cache.c

/* Support for reading /etc/ld.so.cache files written by Linux ldconfig.
Copyright (C) 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 <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);

#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;

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

  if (cache == NULL)
    {
      /* Read the contents of the file.  */
      void *file = _dl_sysdep_read_whole_file ("/etc/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;
	}
    }

  for (i = 0; i < cache->nlibs; ++i)
    if (cache->libs[i].flags == 1 && /* 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)))
      return (const char *) &cache->libs[cache->nlibs] + cache->libs[i].value;

  return NULL;
}