glibc/elf/cache.c

/* Copyright (C) 2022-2023 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

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

   This program 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, see <https://www.gnu.org/licenses/>.  */

#include <assert.h>
#include <errno.h>
#include <error.h>
#include <dirent.h>
#include <inttypes.h>
#include <libgen.h>
#include <libintl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <stdint.h>
#include <sys/fcntl.h>
#include <sys/mman.h>
#include <sys/param.h>
#include <sys/stat.h>
#include <sys/types.h>

#include <ldconfig.h>
#include <dl-cache.h>
#include <version.h>
#include <stringtable.h>

/* Used to store library names, paths, and other strings.  */
static struct stringtable strings;

/* Keeping track of "glibc-hwcaps" subdirectories.  During cache
   construction, a linear search by name is performed to deduplicate
   entries.  */
struct glibc_hwcaps_subdirectory
{
  struct glibc_hwcaps_subdirectory *next;

  /* Interned string with the subdirectory name.  */
  struct stringtable_entry *name;

  /* Array index in the cache_extension_tag_glibc_hwcaps section in
     the stored cached file.  This is computed after all the
     subdirectories have been processed, so that subdirectory names in
     the extension section can be sorted.  */
  uint32_t section_index;

  /* True if the subdirectory is actually used for anything.  */
  bool used;
};

const char *
glibc_hwcaps_subdirectory_name (const struct glibc_hwcaps_subdirectory *dir)
{
  return dir->name->string;
}

/* Linked list of known hwcaps subdirecty names.  */
static struct glibc_hwcaps_subdirectory *hwcaps;

struct glibc_hwcaps_subdirectory *
new_glibc_hwcaps_subdirectory (const char *name)
{
  struct stringtable_entry *name_interned = stringtable_add (&strings, name);
  for (struct glibc_hwcaps_subdirectory *p = hwcaps; p != NULL; p = p->next)
    if (p->name == name_interned)
      return p;
  struct glibc_hwcaps_subdirectory *p = xmalloc (sizeof (*p));
  p->next = hwcaps;
  p->name = name_interned;
  p->section_index = 0;
  p->used = false;
  hwcaps = p;
  return p;
}

/* Helper for sorting struct glibc_hwcaps_subdirectory elements by
   name.  */
static int
assign_glibc_hwcaps_indices_compare (const void *l, const void *r)
{
  const struct glibc_hwcaps_subdirectory *left
    = *(struct glibc_hwcaps_subdirectory **)l;
  const struct glibc_hwcaps_subdirectory *right
    = *(struct glibc_hwcaps_subdirectory **)r;
  return strcmp (glibc_hwcaps_subdirectory_name (left),
		 glibc_hwcaps_subdirectory_name (right));
}

/* Count the number of hwcaps subdirectories which are actually
   used.  */
static size_t
glibc_hwcaps_count (void)
{
  size_t count = 0;
  for (struct glibc_hwcaps_subdirectory *p = hwcaps; p != NULL; p = p->next)
    if (p->used)
      ++count;
  return count;
}

/* Compute the section_index fields for all   */
static void
assign_glibc_hwcaps_indices (void)
{
  /* Convert the linked list into an array, so that we can use qsort.
     Only copy the subdirectories which are actually used.  */
  size_t count = glibc_hwcaps_count ();
  struct glibc_hwcaps_subdirectory **array
    = xmalloc (sizeof (*array) * count);
  {
    size_t i = 0;
    for (struct glibc_hwcaps_subdirectory *p = hwcaps; p != NULL; p = p->next)
      if (p->used)
	{
	  array[i] = p;
	  ++i;
	}
    assert (i == count);
  }

  qsort (array, count, sizeof (*array), assign_glibc_hwcaps_indices_compare);

  /* Assign the array indices.  */
  for (size_t i = 0; i < count; ++i)
    array[i]->section_index = i;

  free (array);
}

struct cache_entry
{
  struct stringtable_entry *lib; /* Library name.  */
  struct stringtable_entry *path; /* Path to find library.  */
  int flags;			/* Flags to indicate kind of library.  */
  unsigned int isa_level;	/* Required ISA level.  */

  /* glibc-hwcaps subdirectory.  */
  struct glibc_hwcaps_subdirectory *hwcaps;

  struct cache_entry *next;	/* Next entry in list.  */
};

/* List of all cache entries.  */
static struct cache_entry *entries;

/* libc4, ELF and libc5 are unsupported.  */
static const char *flag_descr[] =
{ "libc4", "ELF", "libc5", "libc6"};

/* Print a single entry.  */
static void
print_entry (const char *lib, int flag, uint64_t hwcap,
	     const char *hwcap_string, const char *key)
{
  printf ("\t%s (", lib);
  switch (flag & FLAG_TYPE_MASK)
    {
    case FLAG_ELF_LIBC6:
      fputs (flag_descr[flag & FLAG_TYPE_MASK], stdout);
      break;
    default:
      fputs (_("unknown or unsupported flag"), stdout);
      break;
    }
  switch (flag & FLAG_REQUIRED_MASK)
    {
    case FLAG_SPARC_LIB64:
      fputs (",64bit", stdout);
      break;
    case FLAG_IA64_LIB64:
      fputs (",IA-64", stdout);
      break;
    case FLAG_X8664_LIB64:
      fputs (",x86-64", stdout);
      break;
    case FLAG_S390_LIB64:
      fputs (",64bit", stdout);
      break;
    case FLAG_POWERPC_LIB64:
      fputs (",64bit", stdout);
      break;
    case FLAG_MIPS64_LIBN32:
      fputs (",N32", stdout);
      break;
    case FLAG_MIPS64_LIBN64:
      fputs (",64bit", stdout);
      break;
    case FLAG_X8664_LIBX32:
      fputs (",x32", stdout);
      break;
    case FLAG_ARM_LIBHF:
      fputs (",hard-float", stdout);
      break;
    case FLAG_AARCH64_LIB64:
      fputs (",AArch64", stdout);
      break;
    /* Uses the ARM soft-float ABI.  */
    case FLAG_ARM_LIBSF:
      fputs (",soft-float", stdout);
      break;
    case FLAG_MIPS_LIB32_NAN2008:
      fputs (",nan2008", stdout);
      break;
    case FLAG_MIPS64_LIBN32_NAN2008:
      fputs (",N32,nan2008", stdout);
      break;
    case FLAG_MIPS64_LIBN64_NAN2008:
      fputs (",64bit,nan2008", stdout);
      break;
    case FLAG_RISCV_FLOAT_ABI_SOFT:
      fputs (",soft-float", stdout);
      break;
    case FLAG_RISCV_FLOAT_ABI_DOUBLE:
      fputs (",double-float", stdout);
      break;
    case FLAG_LARCH_FLOAT_ABI_SOFT:
      fputs (",soft-float", stdout);
      break;
    case FLAG_LARCH_FLOAT_ABI_DOUBLE:
      fputs (",double-float", stdout);
      break;
    case 0:
      break;
    default:
      printf (",%d", flag & FLAG_REQUIRED_MASK);
      break;
    }
  if (hwcap_string != NULL)
    printf (", hwcap: \"%s\"", hwcap_string);
  else if (hwcap != 0)
    printf (", hwcap: %#.16" PRIx64, hwcap);
  printf (") => %s\n", key);
}

/* Returns the string with the name of the glibcs-hwcaps subdirectory
   associated with ENTRY->hwcap.  file_base must be the base address
   for string table indices.  */
static const char *
glibc_hwcaps_string (struct cache_extension_all_loaded *ext,
		     const void *file_base, size_t file_size,
		     struct file_entry_new *entry)
{
  const uint32_t *hwcaps_array
    = ext->sections[cache_extension_tag_glibc_hwcaps].base;
  if (dl_cache_hwcap_extension (entry) && hwcaps_array != NULL)
    {
      uint32_t index = (uint32_t) entry->hwcap;
      if (index < ext->sections[cache_extension_tag_glibc_hwcaps].size / 4)
	{
	  uint32_t string_table_index = hwcaps_array[index];
	  if (string_table_index < file_size)
	    return file_base + string_table_index;
	}
    }
  return NULL;
}

/* Print an error and exit if the new-file cache is internally
   inconsistent.  */
static void
check_new_cache (struct cache_file_new *cache)
{
  if (! cache_file_new_matches_endian (cache))
    error (EXIT_FAILURE, 0, _("Cache file has wrong endianness.\n"));
}

/* Print the extension information in *EXT.  */
static void
print_extensions (struct cache_extension_all_loaded *ext)
{
  if (ext->sections[cache_extension_tag_generator].base != NULL)
    {
      fputs (_("Cache generated by: "), stdout);
      fwrite (ext->sections[cache_extension_tag_generator].base, 1,
	      ext->sections[cache_extension_tag_generator].size, stdout);
      putchar ('\n');
    }
}

/* Print the whole cache file, if a file contains the new cache format
   hidden in the old one, print the contents of the new format.  */
void
print_cache (const char *cache_name)
{
  int fd = open (cache_name, O_RDONLY);
  if (fd < 0)
    error (EXIT_FAILURE, errno, _("Can't open cache file %s\n"), cache_name);

  struct stat st;
  if (fstat (fd, &st) < 0
      /* No need to map the file if it is empty.  */
      || st.st_size == 0)
    {
      close (fd);
      return;
    }

  struct cache_file *cache
    = mmap (NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
  if (cache == MAP_FAILED)
    error (EXIT_FAILURE, errno, _("mmap of cache file failed.\n"));

  size_t cache_size = st.st_size;
  if (cache_size < sizeof (struct cache_file))
    error (EXIT_FAILURE, 0, _("File is not a cache file.\n"));

  struct cache_file_new *cache_new = NULL;
  const char *cache_data;
  int format = 0;

  if (memcmp (cache->magic, CACHEMAGIC, sizeof CACHEMAGIC - 1))
    {
      /* This can only be the new format without the old one.  */
      cache_new = (struct cache_file_new *) cache;

      if (memcmp (cache_new->magic, CACHEMAGIC_NEW, sizeof CACHEMAGIC_NEW - 1)
	  || memcmp (cache_new->version, CACHE_VERSION,
		      sizeof CACHE_VERSION - 1))
	error (EXIT_FAILURE, 0, _("File is not a cache file.\n"));
      check_new_cache (cache_new);
      format = 1;
      /* This is where the strings start.  */
      cache_data = (const char *) cache_new;
    }
  else
    {
      /* Check for corruption, avoiding overflow.  */
      if ((cache_size - sizeof (struct cache_file)) / sizeof (struct file_entry)
	  < cache->nlibs)
	error (EXIT_FAILURE, 0, _("File is not a cache file.\n"));

      size_t offset = ALIGN_CACHE (sizeof (struct cache_file)
				   + (cache->nlibs
				      * sizeof (struct file_entry)));
      /* This is where the strings start.  */
      cache_data = (const char *) &cache->libs[cache->nlibs];

      /* Check for a new cache embedded in the old format.  */
      if (cache_size
	  > (offset + sizeof (struct cache_file_new)))
	{

	  cache_new = (struct cache_file_new *) ((void *)cache + offset);

	  if (memcmp (cache_new->magic, CACHEMAGIC_NEW,
		      sizeof CACHEMAGIC_NEW - 1) == 0
	      && memcmp (cache_new->version, CACHE_VERSION,
			 sizeof CACHE_VERSION - 1) == 0)
	    {
	      check_new_cache (cache_new);
	      cache_data = (const char *) cache_new;
	      format = 1;
	    }
	}
    }

  if (format == 0)
    {
      printf (_("%d libs found in cache `%s'\n"), cache->nlibs, cache_name);

      /* Print everything.  */
      for (unsigned int i = 0; i < cache->nlibs; i++)
	print_entry (cache_data + cache->libs[i].key,
		     cache->libs[i].flags, 0, NULL,
		     cache_data + cache->libs[i].value);
    }
  else if (format == 1)
    {
      struct cache_extension_all_loaded ext;
      if (!cache_extension_load (cache_new, cache, cache_size, &ext))
	error (EXIT_FAILURE, 0,
	       _("Malformed extension data in cache file %s\n"), cache_name);

      printf (_("%d libs found in cache `%s'\n"),
	      cache_new->nlibs, cache_name);

      /* Print everything.  */
      for (unsigned int i = 0; i < cache_new->nlibs; i++)
	{
	  const char *hwcaps_string
	    = glibc_hwcaps_string (&ext, cache, cache_size,
				   &cache_new->libs[i]);
	  print_entry (cache_data + cache_new->libs[i].key,
		       cache_new->libs[i].flags,
		       cache_new->libs[i].hwcap, hwcaps_string,
		       cache_data + cache_new->libs[i].value);
	}
      print_extensions (&ext);
    }
  /* Cleanup.  */
  munmap (cache, cache_size);
  close (fd);
}

/* Initialize cache data structures.  */
void
init_cache (void)
{
  entries = NULL;
}

static int
compare (const struct cache_entry *e1, const struct cache_entry *e2)
{
  /* We need to swap entries here to get the correct sort order.  */
  int res = _dl_cache_libcmp (e2->lib->string, e1->lib->string);
  if (res == 0)
    {
      if (e1->flags < e2->flags)
	return 1;
      else if (e1->flags > e2->flags)
	return -1;
      /* Keep the glibc-hwcaps extension entries before the regular
	 entries, and sort them by their names.  search_cache in
	 dl-cache.c stops searching once the first non-extension entry
	 is found, so the extension entries need to come first.  */
      else if (e1->hwcaps != NULL && e2->hwcaps == NULL)
	return -1;
      else if (e1->hwcaps == NULL && e2->hwcaps != NULL)
	return 1;
      else if (e1->hwcaps != NULL && e2->hwcaps != NULL)
	{
	  res = strcmp (glibc_hwcaps_subdirectory_name (e1->hwcaps),
			glibc_hwcaps_subdirectory_name (e2->hwcaps));
	  if (res != 0)
	    return res;
	}
    }
  return res;
}

/* Size of the cache extension directory.  All tags are assumed to be
   present.  */
enum
  {
   cache_extension_size = (offsetof (struct cache_extension, sections)
			   + (cache_extension_count
			      * sizeof (struct cache_extension_section)))
  };

/* Write the cache extensions to FD.  The string table is shifted by
   STRING_TABLE_OFFSET.  The extension directory is assumed to be
   located at CACHE_EXTENSION_OFFSET.  assign_glibc_hwcaps_indices
   must have been called.  */
static void
write_extensions (int fd, uint32_t str_offset,
		  uint32_t cache_extension_offset)
{
  assert ((cache_extension_offset % 4) == 0);

  /* The length and contents of the glibc-hwcaps section.  */
  uint32_t hwcaps_count = glibc_hwcaps_count ();
  uint32_t hwcaps_offset = cache_extension_offset + cache_extension_size;
  uint32_t hwcaps_size = hwcaps_count * sizeof (uint32_t);
  uint32_t *hwcaps_array = xmalloc (hwcaps_size);
  for (struct glibc_hwcaps_subdirectory *p = hwcaps; p != NULL; p = p->next)
    if (p->used)
      hwcaps_array[p->section_index] = str_offset + p->name->offset;

  /* This is the offset of the generator string.  */
  uint32_t generator_offset = hwcaps_offset;
  if (hwcaps_count == 0)
    /* There is no section for the hwcaps subdirectories.  */
    generator_offset -= sizeof (struct cache_extension_section);
  else
    /* The string table indices for the hwcaps subdirectories shift
       the generator string backwards.  */
    generator_offset += hwcaps_size;

  struct cache_extension *ext = xmalloc (cache_extension_size);
  ext->magic = cache_extension_magic;

  /* Extension index current being filled.  */
  size_t xid = 0;

  const char *generator
    = "ldconfig " PKGVERSION RELEASE " release version " VERSION;
  ext->sections[xid].tag = cache_extension_tag_generator;
  ext->sections[xid].flags = 0;
  ext->sections[xid].offset = generator_offset;
  ext->sections[xid].size = strlen (generator);

  if (hwcaps_count > 0)
    {
      ++xid;
      ext->sections[xid].tag = cache_extension_tag_glibc_hwcaps;
      ext->sections[xid].flags = 0;
      ext->sections[xid].offset = hwcaps_offset;
      ext->sections[xid].size = hwcaps_size;
    }

  ++xid;
  ext->count = xid;
  assert (xid <= cache_extension_count);

  size_t ext_size = (offsetof (struct cache_extension, sections)
		     + xid * sizeof (struct cache_extension_section));
  if (write (fd, ext, ext_size) != ext_size
      || write (fd, hwcaps_array, hwcaps_size) != hwcaps_size
      || write (fd, generator, strlen (generator)) != strlen (generator))
    error (EXIT_FAILURE, errno, _("Writing of cache extension data failed"));

  free (hwcaps_array);
  free (ext);
}

/* Compute the hwcap value from ENTRY.  */
static inline uint64_t
compute_hwcap_value (struct cache_entry *entry)
{
  if (entry->isa_level > DL_CACHE_HWCAP_ISA_LEVEL_MASK)
    error (EXIT_FAILURE, 0, _("%s: ISA level is too high (%d > %d)"),
	   entry->path->string, entry->isa_level,
	   DL_CACHE_HWCAP_ISA_LEVEL_MASK);
  return (DL_CACHE_HWCAP_EXTENSION
	  | (((uint64_t) entry->isa_level) << 32)
	  | entry->hwcaps->section_index);
}

/* Save the contents of the cache.  */
void
save_cache (const char *cache_name)
{
  /* The cache entries are sorted already, save them in this order. */

  assign_glibc_hwcaps_indices ();

  struct cache_entry *entry;
  /* Number of cache entries.  */
  int cache_entry_count = 0;
  /* The old format doesn't contain hwcap entries and doesn't contain
     libraries in subdirectories with hwcaps entries.  Count therefore
     all entries.  */
  int cache_entry_old_count = 0;

  for (entry = entries; entry != NULL; entry = entry->next)
    {
      ++cache_entry_count;
      ++cache_entry_old_count;
    }

  struct stringtable_finalized strings_finalized;
  stringtable_finalize (&strings, &strings_finalized);

  /* Create the on disk cache structure.  */
  struct cache_file *file_entries = NULL;
  size_t file_entries_size = 0;

  if (opt_format != opt_format_new)
    {
      /* struct cache_file_new is 64-bit aligned on some arches while
	 only 32-bit aligned on other arches.  Duplicate last old
	 cache entry so that new cache in ld.so.cache can be used by
	 both.  */
      if (opt_format != opt_format_old)
	cache_entry_old_count = (cache_entry_old_count + 1) & ~1;

      /* And the list of all entries in the old format.  */
      file_entries_size = sizeof (struct cache_file)
	+ cache_entry_old_count * sizeof (struct file_entry);
      file_entries = xmalloc (file_entries_size);

      /* Fill in the header.  */
      memset (file_entries, '\0', sizeof (struct cache_file));
      memcpy (file_entries->magic, CACHEMAGIC, sizeof CACHEMAGIC - 1);

      file_entries->nlibs = cache_entry_old_count;
    }

  struct cache_file_new *file_entries_new = NULL;
  size_t file_entries_new_size = 0;

  if (opt_format != opt_format_old)
    {
      /* And the list of all entries in the new format.  */
      file_entries_new_size = sizeof (struct cache_file_new)
	+ cache_entry_count * sizeof (struct file_entry_new);
      file_entries_new = xmalloc (file_entries_new_size);

      /* Fill in the header.  */
      memset (file_entries_new, '\0', sizeof (struct cache_file_new));
      memcpy (file_entries_new->magic, CACHEMAGIC_NEW,
	      sizeof CACHEMAGIC_NEW - 1);
      memcpy (file_entries_new->version, CACHE_VERSION,
	      sizeof CACHE_VERSION - 1);

      file_entries_new->nlibs = cache_entry_count;
      file_entries_new->len_strings = strings_finalized.size;
      file_entries_new->flags = cache_file_new_flags_endian_current;
    }

  /* Pad for alignment of cache_file_new.  */
  size_t pad = ALIGN_CACHE (file_entries_size) - file_entries_size;

  /* If we have both formats, we hide the new format in the strings
     table, we have to adjust all string indices for this so that
     old libc5/glibc 2 dynamic linkers just ignore them.  */
  unsigned int str_offset;
  if (opt_format != opt_format_old)
    str_offset = file_entries_new_size;
  else
    str_offset = 0;

  /* An array for all strings.  */
  int idx_old;
  int idx_new;

  for (idx_old = 0, idx_new = 0, entry = entries; entry != NULL;
       entry = entry->next, ++idx_new)
    {
      if (opt_format != opt_format_new)
	{
	  file_entries->libs[idx_old].flags = entry->flags;
	  /* XXX: Actually we can optimize here and remove duplicates.  */
	  file_entries->libs[idx_old].key = str_offset + pad;
	  file_entries->libs[idx_new].key = str_offset + entry->lib->offset;
	  file_entries->libs[idx_new].value
	    = str_offset + entry->path->offset;
	}
      if (opt_format != opt_format_old)
	{
	  /* We could subtract file_entries_new_size from str_offset -
	     not doing so makes the code easier, the string table
	     always begins at the beginning of the new cache
	     struct.  */
	  file_entries_new->libs[idx_new].flags = entry->flags;
	  file_entries_new->libs[idx_new].osversion_unused = 0;
	  if (entry->hwcaps == NULL)
	    file_entries_new->libs[idx_new].hwcap = 0;
	  else
	    file_entries_new->libs[idx_new].hwcap
	      = compute_hwcap_value (entry);
	  file_entries_new->libs[idx_new].key
	    = str_offset + entry->lib->offset;
	  file_entries_new->libs[idx_new].value
	    = str_offset + entry->path->offset;
	}

      ++idx_old;
    }

  /* Duplicate last old cache entry if needed.  */
  if (opt_format != opt_format_new
      && idx_old < cache_entry_old_count)
    file_entries->libs[idx_old] = file_entries->libs[idx_old - 1];

  /* Compute the location of the extension directory.  This
     implementation puts the directory after the string table.  The
     size computation matches the write calls below.  The extension
     directory does not exist with format 0, so the value does not
     matter.  */
  uint32_t extension_offset = 0;
  if (opt_format != opt_format_new)
    extension_offset += file_entries_size;
  if (opt_format != opt_format_old)
    {
      if (opt_format != opt_format_new)
	extension_offset += pad;
      extension_offset += file_entries_new_size;
    }
  extension_offset += strings_finalized.size;
  extension_offset = roundup (extension_offset, 4); /* Provide alignment.  */
  if (opt_format != opt_format_old)
    file_entries_new->extension_offset = extension_offset;

  /* Write out the cache.  */

  /* Write cache first to a temporary file and rename it later.  */
  char *temp_name = xmalloc (strlen (cache_name) + 2);
  sprintf (temp_name, "%s~", cache_name);

  /* Create file.  */
  int fd = open (temp_name, O_CREAT|O_WRONLY|O_TRUNC|O_NOFOLLOW,
		 S_IRUSR|S_IWUSR);
  if (fd < 0)
    error (EXIT_FAILURE, errno, _("Can't create temporary cache file %s"),
	   temp_name);

  /* Write contents.  */
  if (opt_format != opt_format_new)
    {
      if (write (fd, file_entries, file_entries_size)
	  != (ssize_t) file_entries_size)
	error (EXIT_FAILURE, errno, _("Writing of cache data failed"));
    }
  if (opt_format != opt_format_old)
    {
      /* Align cache.  */
      if (opt_format != opt_format_new)
	{
	  char zero[pad];
	  memset (zero, '\0', pad);
	  if (write (fd, zero, pad) != (ssize_t) pad)
	    error (EXIT_FAILURE, errno, _("Writing of cache data failed"));
	}
      if (write (fd, file_entries_new, file_entries_new_size)
	  != (ssize_t) file_entries_new_size)
	error (EXIT_FAILURE, errno, _("Writing of cache data failed"));
    }

  if (write (fd, strings_finalized.strings, strings_finalized.size)
      != (ssize_t) strings_finalized.size)
    error (EXIT_FAILURE, errno, _("Writing of cache data failed"));

  if (opt_format != opt_format_old)
    {
      /* Align file position to 4.  */
      __attribute__ ((unused)) off64_t old_offset
        = lseek64 (fd, extension_offset, SEEK_SET);
      assert ((unsigned long long int) (extension_offset - old_offset) < 4);
      write_extensions (fd, str_offset, extension_offset);
    }

  /* Make sure user can always read cache file */
  if (chmod (temp_name, S_IROTH|S_IRGRP|S_IRUSR|S_IWUSR))
    error (EXIT_FAILURE, errno,
	   _("Changing access rights of %s to %#o failed"), temp_name,
	   S_IROTH|S_IRGRP|S_IRUSR|S_IWUSR);

  /* Make sure that data is written to disk.  */
  if (fsync (fd) != 0 || close (fd) != 0)
    error (EXIT_FAILURE, errno, _("Writing of cache data failed"));

  /* Move temporary to its final location.  */
  if (rename (temp_name, cache_name))
    error (EXIT_FAILURE, errno, _("Renaming of %s to %s failed"), temp_name,
	   cache_name);

  /* Free all allocated memory.  */
  free (file_entries_new);
  free (file_entries);
  free (strings_finalized.strings);
  free (temp_name);

  while (entries)
    {
      entry = entries;
      entries = entries->next;
      free (entry);
    }
}


/* Add one library to the cache.  */
void
add_to_cache (const char *path, const char *filename, const char *soname,
	      int flags, unsigned int isa_level,
	      struct glibc_hwcaps_subdirectory *hwcaps)
{
  struct cache_entry *new_entry = xmalloc (sizeof (*new_entry));

  struct stringtable_entry *path_interned;
  {
    char *p;
    if (asprintf (&p, "%s/%s", path, filename) < 0)
      error (EXIT_FAILURE, errno, _("Could not create library path"));
    path_interned = stringtable_add (&strings, p);
    free (p);
  }

  new_entry->lib = stringtable_add (&strings, soname);
  new_entry->path = path_interned;
  new_entry->flags = flags;
  new_entry->isa_level = isa_level;
  new_entry->hwcaps = hwcaps;

  if (hwcaps != NULL)
    hwcaps->used = true;

  /* Keep the list sorted - search for right place to insert.  */
  struct cache_entry *ptr = entries;
  struct cache_entry *prev = entries;
  while (ptr != NULL)
    {
      if (compare (ptr, new_entry) > 0)
	break;
      prev = ptr;
      ptr = ptr->next;
    }
  /* Is this the first entry?  */
  if (ptr == entries)
    {
      new_entry->next = entries;
      entries = new_entry;
    }
  else
    {
      new_entry->next = prev->next;
      prev->next = new_entry;
    }
}


/* Auxiliary cache.  */

struct aux_cache_entry_id
{
  uint64_t ino;
  uint64_t ctime;
  uint64_t size;
  uint64_t dev;
};

struct aux_cache_entry
{
  struct aux_cache_entry_id id;
  int flags;
  unsigned int isa_level;
  int used;
  char *soname;
  struct aux_cache_entry *next;
};

#define AUX_CACHEMAGIC		"glibc-ld.so.auxcache-1.0"

struct aux_cache_file_entry
{
  struct aux_cache_entry_id id;	/* Unique id of entry.  */
  int32_t flags;		/* This is 1 for an ELF library.  */
  uint32_t soname;		/* String table indice.  */
  uint32_t isa_level;		/* Required ISA level.	 */
};

/* ldconfig maintains an auxiliary cache file that allows
   only reading those libraries that have changed since the last iteration.
   For this for each library some information is cached in the auxiliary
   cache.  */
struct aux_cache_file
{
  char magic[sizeof AUX_CACHEMAGIC - 1];
  uint32_t nlibs;		/* Number of entries.  */
  uint32_t len_strings;		/* Size of string table. */
  struct aux_cache_file_entry libs[0]; /* Entries describing libraries.  */
  /* After this the string table of size len_strings is found.	*/
};

static const unsigned int primes[] =
{
  1021, 2039, 4093, 8191, 16381, 32749, 65521, 131071, 262139,
  524287, 1048573, 2097143, 4194301, 8388593, 16777213, 33554393,
  67108859, 134217689, 268435399, 536870909, 1073741789, 2147483647
};

static size_t aux_hash_size;
static struct aux_cache_entry **aux_hash;

/* Simplistic hash function for aux_cache_entry_id.  */
static unsigned int
aux_cache_entry_id_hash (struct aux_cache_entry_id *id)
{
  uint64_t ret = ((id->ino * 11 + id->ctime) * 11 + id->size) * 11 + id->dev;
  return ret ^ (ret >> 32);
}

static size_t nextprime (size_t x)
{
  for (unsigned int i = 0; i < sizeof (primes) / sizeof (primes[0]); ++i)
    if (primes[i] >= x)
      return primes[i];
  return x;
}

void
init_aux_cache (void)
{
  aux_hash_size = primes[3];
  aux_hash = xcalloc (aux_hash_size, sizeof (struct aux_cache_entry *));
}

int
search_aux_cache (struct stat *stat_buf, int *flags, unsigned int *isa_level,
		  char **soname)
{
  struct aux_cache_entry_id id;
  id.ino = (uint64_t) stat_buf->st_ino;
  id.ctime = (uint64_t) stat_buf->st_ctime;
  id.size = (uint64_t) stat_buf->st_size;
  id.dev = (uint64_t) stat_buf->st_dev;

  unsigned int hash = aux_cache_entry_id_hash (&id);
  struct aux_cache_entry *entry;
  for (entry = aux_hash[hash % aux_hash_size]; entry; entry = entry->next)
    if (id.ino == entry->id.ino
	&& id.ctime == entry->id.ctime
	&& id.size == entry->id.size
	&& id.dev == entry->id.dev)
      {
	*flags = entry->flags;
	*isa_level = entry->isa_level;
	if (entry->soname != NULL)
	  *soname = xstrdup (entry->soname);
	else
	  *soname = NULL;
	entry->used = 1;
	return 1;
      }

  return 0;
}

static void
insert_to_aux_cache (struct aux_cache_entry_id *id, int flags,
		     unsigned int isa_level, const char *soname, int used)
{
  size_t hash = aux_cache_entry_id_hash (id) % aux_hash_size;
  struct aux_cache_entry *entry;
  for (entry = aux_hash[hash]; entry; entry = entry->next)
    if (id->ino == entry->id.ino
	&& id->ctime == entry->id.ctime
	&& id->size == entry->id.size
	&& id->dev == entry->id.dev)
      abort ();

  size_t len = soname ? strlen (soname) + 1 : 0;
  entry = xmalloc (sizeof (struct aux_cache_entry) + len);
  entry->id = *id;
  entry->flags = flags;
  entry->isa_level = isa_level;
  entry->used = used;
  if (soname != NULL)
    entry->soname = memcpy ((char *) (entry + 1), soname, len);
  else
    entry->soname = NULL;
  entry->next = aux_hash[hash];
  aux_hash[hash] = entry;
}

void
add_to_aux_cache (struct stat *stat_buf, int flags, unsigned int isa_level,
		  const char *soname)
{
  struct aux_cache_entry_id id;
  id.ino = (uint64_t) stat_buf->st_ino;
  id.ctime = (uint64_t) stat_buf->st_ctime;
  id.size = (uint64_t) stat_buf->st_size;
  id.dev = (uint64_t) stat_buf->st_dev;
  insert_to_aux_cache (&id, flags, isa_level, soname, 1);
}

/* Load auxiliary cache to search for unchanged entries.   */
void
load_aux_cache (const char *aux_cache_name)
{
  int fd = open (aux_cache_name, O_RDONLY);
  if (fd < 0)
    {
      init_aux_cache ();
      return;
    }

  struct stat st;
  if (fstat (fd, &st) < 0 || st.st_size < sizeof (struct aux_cache_file))
    {
      close (fd);
      init_aux_cache ();
      return;
    }

  size_t aux_cache_size = st.st_size;
  struct aux_cache_file *aux_cache
    = mmap (NULL, aux_cache_size, PROT_READ, MAP_PRIVATE, fd, 0);
  if (aux_cache == MAP_FAILED
      || aux_cache_size < sizeof (struct aux_cache_file)
      || memcmp (aux_cache->magic, AUX_CACHEMAGIC, sizeof AUX_CACHEMAGIC - 1)
      || aux_cache_size != (sizeof (struct aux_cache_file)
			    + aux_cache->nlibs * sizeof (struct aux_cache_file_entry)
			    + aux_cache->len_strings))
    {
      if (aux_cache != MAP_FAILED)
	munmap (aux_cache, aux_cache_size);

      close (fd);
      init_aux_cache ();
      return;
    }

  aux_hash_size = nextprime (aux_cache->nlibs);
  aux_hash = xcalloc (aux_hash_size, sizeof (struct aux_cache_entry *));

  const char *aux_cache_data
    = (const char *) &aux_cache->libs[aux_cache->nlibs];
  for (unsigned int i = 0; i < aux_cache->nlibs; ++i)
    insert_to_aux_cache (&aux_cache->libs[i].id,
			 aux_cache->libs[i].flags,
			 aux_cache->libs[i].isa_level,
			 aux_cache->libs[i].soname == 0
			 ? NULL : aux_cache_data + aux_cache->libs[i].soname,
			 0);

  munmap (aux_cache, aux_cache_size);
  close (fd);
}

/* Save the contents of the auxiliary cache.  */
void
save_aux_cache (const char *aux_cache_name)
{
  /* Count the length of all sonames.  We start with empty string.  */
  size_t total_strlen = 1;
  /* Number of cache entries.  */
  int cache_entry_count = 0;

  for (size_t i = 0; i < aux_hash_size; ++i)
    for (struct aux_cache_entry *entry = aux_hash[i];
	 entry != NULL; entry = entry->next)
      if (entry->used)
	{
	  ++cache_entry_count;
	  if (entry->soname != NULL)
	    total_strlen += strlen (entry->soname) + 1;
	}

  /* Auxiliary cache.  */
  size_t file_entries_size
    = sizeof (struct aux_cache_file)
      + cache_entry_count * sizeof (struct aux_cache_file_entry);
  struct aux_cache_file *file_entries
    = xmalloc (file_entries_size + total_strlen);

  /* Fill in the header of the auxiliary cache.  */
  memset (file_entries, '\0', sizeof (struct aux_cache_file));
  memcpy (file_entries->magic, AUX_CACHEMAGIC, sizeof AUX_CACHEMAGIC - 1);

  file_entries->nlibs = cache_entry_count;
  file_entries->len_strings = total_strlen;

  /* Initial String offset for auxiliary cache is always after the
     special empty string.  */
  unsigned int str_offset = 1;

  /* An array for all strings.  */
  char *str = (char *) file_entries + file_entries_size;
  *str++ = '\0';

  size_t idx = 0;
  for (size_t i = 0; i < aux_hash_size; ++i)
    for (struct aux_cache_entry *entry = aux_hash[i];
	 entry != NULL; entry = entry->next)
      if (entry->used)
	{
	  file_entries->libs[idx].id = entry->id;
	  file_entries->libs[idx].flags = entry->flags;
	  if (entry->soname == NULL)
	    file_entries->libs[idx].soname = 0;
	  else
	    {
	      file_entries->libs[idx].soname = str_offset;

	      size_t len = strlen (entry->soname) + 1;
	      str = mempcpy (str, entry->soname, len);
	      str_offset += len;
	    }
	  file_entries->libs[idx++].isa_level = entry->isa_level;
	}

  /* Write out auxiliary cache file.  */
  /* Write auxiliary cache first to a temporary file and rename it later.  */

  char *temp_name = xmalloc (strlen (aux_cache_name) + 2);
  sprintf (temp_name, "%s~", aux_cache_name);

  /* Check that directory exists and create if needed.  */
  char *dir = strdupa (aux_cache_name);
  dir = dirname (dir);

  struct stat st;
  if (stat (dir, &st) < 0)
    {
      if (mkdir (dir, 0700) < 0)
	goto out_fail;
    }

  /* Create file.  */
  int fd = open (temp_name, O_CREAT|O_WRONLY|O_TRUNC|O_NOFOLLOW,
		 S_IRUSR|S_IWUSR);
  if (fd < 0)
    goto out_fail;

  bool fail = ((write (fd, file_entries, file_entries_size + total_strlen)
		!= (ssize_t) (file_entries_size + total_strlen))
	       || fdatasync (fd) != 0);

  fail |= close (fd) != 0;

  if (fail)
    {
      unlink (temp_name);
      goto out_fail;
    }

  /* Move temporary to its final location.  */
  if (rename (temp_name, aux_cache_name))
    unlink (temp_name);

out_fail:
  /* Free allocated memory.  */
  free (temp_name);
  free (file_entries);
}