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elf: Implement tail merging of strings in ldconfig

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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>
This commit is contained in:
Florian Weimer 2020-12-04 09:13:43 +01:00
parent 785969a047
commit 73b6e50a22
2 changed files with 39 additions and 38 deletions
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3
elf/Makefile
View file

@ -120,7 +120,8 @@ 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

74
elf/cache.c
View file

@ -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);
struct cache_entry *new_entry = xmalloc (sizeof (*new_entry));
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 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;