commit 73b6e50a22dea9ae6144beaaa675d2ac62c281ca

Author: Florian Weimer <fweimer@redhat.com>

Date:   Fri Dec 4 09:13:43 2020 +0100

    elf: Implement tail merging of strings in ldconfig

    This simplifies the string table construction in elf/cache.c

    because there is no more need to keep track of offsets explicitly;

    the string table implementation does this internally.

    This change slightly reduces the size of the cache on disk.  The

    file format does not change as a result.  The strings are

    null-terminated, without explicit length, so tail merging is

    transparent to readers.

    Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

diff --git a/elf/Makefile b/elf/Makefile

index abb3e9d1179ef5cd..a3e802a9a99b759c 100644

--- a/elf/Makefile

+++ b/elf/Makefile

@@ -112,7 +112,8 @@ others-static	+= ldconfig

 others		+= ldconfig

 install-rootsbin += ldconfig

-ldconfig-modules := cache readlib xmalloc xstrdup chroot_canon static-stubs

+ldconfig-modules := cache readlib xmalloc xstrdup chroot_canon static-stubs \

+  stringtable

 extra-objs	+= $(ldconfig-modules:=.o)

 others-extras   = $(ldconfig-modules)

 endif

diff --git a/elf/cache.c b/elf/cache.c

index 5a8f1ad70cc3fead..f773cacacf26db1c 100644

--- a/elf/cache.c

+++ b/elf/cache.c

@@ -35,11 +35,15 @@

 #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;

 struct cache_entry

 {

-  char *lib;			/* Library name.  */

-  char *path;			/* Path to find library.  */

+  struct stringtable_entry *lib; /* Library name.  */

+  struct stringtable_entry *path; /* Path to find library.  */

   int flags;			/* Flags to indicate kind of library.  */

   unsigned int osversion;	/* Required OS version.  */

   uint64_t hwcap;		/* Important hardware capabilities.  */

@@ -300,7 +304,7 @@ 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, e1->lib);

+  int res = _dl_cache_libcmp (e2->lib->string, e1->lib->string);

   if (res == 0)

     {

       if (e1->flags < e2->flags)

@@ -369,26 +373,24 @@ save_cache (const char *cache_name)

 {

   /* The cache entries are sorted already, save them in this order. */

-  /* Count the length of all strings.  */

-  /* The old format doesn't contain hwcap entries and doesn't contain

-     libraries in subdirectories with hwcaps entries.  Count therefore

-     also all entries with hwcap == 0.  */

-  size_t total_strlen = 0;

   struct cache_entry *entry;

   /* Number of cache entries.  */

   int cache_entry_count = 0;

-  /* Number of normal cache entries.  */

+  /* The old format doesn't contain hwcap entries and doesn't contain

+     libraries in subdirectories with hwcaps entries.  Count therefore

+     also all entries with hwcap == 0.  */

   int cache_entry_old_count = 0;

   for (entry = entries; entry != NULL; entry = entry->next)

     {

-      /* Account the final NULs.  */

-      total_strlen += strlen (entry->lib) + strlen (entry->path) + 2;

       ++cache_entry_count;

       if (entry->hwcap == 0)

 	++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;

@@ -432,7 +434,7 @@ save_cache (const char *cache_name)

 	      sizeof CACHE_VERSION - 1);

       file_entries_new->nlibs = cache_entry_count;

-      file_entries_new->len_strings = total_strlen;

+      file_entries_new->len_strings = strings_finalized.size;

       file_entries_new->flags = cache_file_new_flags_endian_current;

     }

@@ -449,20 +451,20 @@ save_cache (const char *cache_name)

     str_offset = 0;

   /* An array for all strings.  */

-  char *strings = xmalloc (total_strlen);

-  char *str = strings;

   int idx_old;

   int idx_new;

   for (idx_old = 0, idx_new = 0, entry = entries; entry != NULL;

        entry = entry->next, ++idx_new)

     {

-      /* First the library.  */

       if (opt_format != opt_format_new && entry->hwcap == 0)

 	{

 	  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)

 	{

@@ -473,20 +475,12 @@ save_cache (const char *cache_name)

 	  file_entries_new->libs[idx_new].flags = entry->flags;

 	  file_entries_new->libs[idx_new].osversion = entry->osversion;

 	  file_entries_new->libs[idx_new].hwcap = entry->hwcap;

-	  file_entries_new->libs[idx_new].key = str_offset;

+	  file_entries_new->libs[idx_new].key

+	    = str_offset + entry->lib->offset;

+	  file_entries_new->libs[idx_new].value

+	    = str_offset + entry->path->offset;

 	}

-      size_t len = strlen (entry->lib) + 1;

-      str = mempcpy (str, entry->lib, len);

-      str_offset += len;

-      /* Then the path.  */

-      if (opt_format != opt_format_new && entry->hwcap == 0)

-	file_entries->libs[idx_old].value = str_offset + pad;

-      if (opt_format != opt_format_old)

-	file_entries_new->libs[idx_new].value = str_offset;

-      len = strlen (entry->path) + 1;

-      str = mempcpy (str, entry->path, len);

-      str_offset += len;

       /* Ignore entries with hwcap for old format.  */

       if (entry->hwcap == 0)

 	++idx_old;

@@ -511,7 +505,7 @@ save_cache (const char *cache_name)

 	extension_offset += pad;

       extension_offset += file_entries_new_size;

     }

-  extension_offset += total_strlen;

+  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;

@@ -551,7 +545,8 @@ save_cache (const char *cache_name)

 	error (EXIT_FAILURE, errno, _("Writing of cache data failed"));

     }

-  if (write (fd, strings, total_strlen) != (ssize_t) total_strlen)

+  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)

@@ -580,7 +575,7 @@ save_cache (const char *cache_name)

   /* Free all allocated memory.  */

   free (file_entries_new);

   free (file_entries);

-  free (strings);

+  free (strings_finalized.strings);

   while (entries)

     {

@@ -596,14 +591,19 @@ void

 add_to_cache (const char *path, const char *lib, int flags,

 	      unsigned int osversion, uint64_t hwcap)

 {

-  size_t liblen = strlen (lib) + 1;

-  size_t len = liblen + strlen (path) + 1;

-  struct cache_entry *new_entry

-    = xmalloc (sizeof (struct cache_entry) + liblen + len);

-

-  new_entry->lib = memcpy ((char *) (new_entry + 1), lib, liblen);

-  new_entry->path = new_entry->lib + liblen;

-  snprintf (new_entry->path, len, "%s/%s", path, lib);

+  struct cache_entry *new_entry = xmalloc (sizeof (*new_entry));

+

+  struct stringtable_entry *path_interned;

+  {

+    char *p;

+    if (asprintf (&p, "%s/%s", path, lib) < 0)

+      error (EXIT_FAILURE, errno, _("Could not create library path"));

+    path_interned = stringtable_add (&strings, p);

+    free (p);

+  }

+

+  new_entry->lib = stringtable_add (&strings, lib);

+  new_entry->path = path_interned;

   new_entry->flags = flags;

   new_entry->osversion = osversion;

   new_entry->hwcap = hwcap;