[PATCH 07/11] elf: Implement tail merging of strings in ldconfig
Adhemerval Zanella
adhemerval.zanella@linaro.org
Mon Nov 30 18:41:08 GMT 2020
On 09/11/2020 15:41, Florian Weimer via Libc-alpha wrote:
> 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.
Any idea of the size improvement here?
LGTM, thanks.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
> ---
> elf/Makefile | 3 ++-
> elf/cache.c | 76 ++++++++++++++++++++++++++--------------------------
> 2 files changed, 40 insertions(+), 39 deletions(-)
>
> diff --git a/elf/Makefile b/elf/Makefile
> index 5a8f116a67..e26ac16b44 100644
> --- a/elf/Makefile
> +++ b/elf/Makefile
> @@ -118,7 +118,8 @@ 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
Ok.
> diff --git a/elf/cache.c b/elf/cache.c
> index 549e04ce21..5a6ee20e86 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
Ok.
> 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)
Ok.
> @@ -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;
> }
>
Ok.
> @@ -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)
> {
Ok.
> @@ -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;
Ok.
> @@ -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;
Ok.
> @@ -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)
Ok.
> @@ -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)
> {
Ok.
> @@ -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;
>
Ok.
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