elf: Add endianness markup to ld.so.cache (bug 27008)

Use a reserved byte in the new format cache header to indicate whether
the file is in little endian or big endian format.  Eventually, this
information could be used to provide a unified cache for qemu-user
and similiar scenarios.

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

diff --git a/elf/cache.c b/elf/cache.c
index c241c17ef9061a7c5ef41fd49dbb9dd624466c76..ffecbe6d82d487ad654db331f204038202f12580 100644 (file)
--- a/elf/cache.c
+++ b/elf/cache.c
@@ -152,6 +152,14 @@ print_entry (const char *lib, int flag, unsigned int osversion,
   printf (") => %s\n", key);
 }
 
+/* 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 whole cache file, if a file contains the new cache format
    hidden in the old one, print the contents of the new format.  */
@@ -193,6 +201,7 @@ print_cache (const char *cache_name)
          || 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;
@@ -222,6 +231,7 @@ print_cache (const char *cache_name)
              && memcmp (cache_new->version, CACHE_VERSION,
                         sizeof CACHE_VERSION - 1) == 0)
            {
+             check_new_cache (cache_new);
              cache_data = (const char *) cache_new;
              format = 1;
            }
@@ -361,6 +371,7 @@ save_cache (const char *cache_name)
 
       file_entries_new->nlibs = cache_entry_count;
       file_entries_new->len_strings = total_strlen;
+      file_entries_new->flags = cache_file_new_flags_endian_current;
     }
 
   /* Pad for alignment of cache_file_new.  */

diff --git a/elf/dl-cache.c b/elf/dl-cache.c
index 45894ecd2fb4e0396aef0eaa17f85c146332d328..02c46ffb0c3dff9bb83831e81c29d37cd6b1aa66 100644 (file)
--- a/elf/dl-cache.c
+++ b/elf/dl-cache.c
@@ -242,6 +242,11 @@ _dl_load_cache_lookup (const char *name)
          && ((cachesize - sizeof *cache_new) / sizeof (struct file_entry_new)
              >= ((struct cache_file_new *) file)->nlibs))
        {
+         if (! cache_file_new_matches_endian (file))
+           {
+             __munmap (file, cachesize);
+             file = (void *) -1;
+           }
          cache_new = file;
          cache = file;
        }
@@ -263,7 +268,20 @@ _dl_load_cache_lookup (const char *name)
          if (cachesize < (offset + sizeof (struct cache_file_new))
              || memcmp (cache_new->magic, CACHEMAGIC_VERSION_NEW,
                         sizeof CACHEMAGIC_VERSION_NEW - 1) != 0)
-           cache_new = (void *) -1;
+             cache_new = (void *) -1;
+         else
+           {
+             if (! cache_file_new_matches_endian (cache_new))
+               {
+                 /* The old-format part of the cache is bogus as well
+                    if the endianness does not match.  (But it is
+                    unclear how the new header can be located if the
+                    endianess does not match.)  */
+                 cache = (void *) -1;
+                 cache_new = (void *) -1;
+                 __munmap (file, cachesize);
+               }
+           }
        }
       else
        {

diff --git a/sysdeps/generic/dl-cache.h b/sysdeps/generic/dl-cache.h
index 4ddd96b0058e31521f051843d62a35e73daec608..4c77cd0c1b98c21d25cb32feb87576540ee3e197 100644 (file)
--- a/sysdeps/generic/dl-cache.h
+++ b/sysdeps/generic/dl-cache.h
@@ -16,6 +16,11 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
+#ifndef _DL_CACHE_H
+#define _DL_CACHE_H
+
+#include <endian.h>
+#include <stdbool.h>
 #include <stdint.h>
 
 #ifndef _DL_CACHE_DEFAULT_ID
@@ -92,17 +97,72 @@ struct file_entry_new
   uint64_t hwcap;              /* Hwcap entry.  */
 };
 
+/* See flags member of struct cache_file_new below.  */
+enum
+  {
+    /* No endianness information available.  An old ldconfig version
+       without endianness support wrote the file.  */
+    cache_file_new_flags_endian_unset = 0,
+
+    /* Cache is invalid and should be ignored.  */
+    cache_file_new_flags_endian_invalid = 1,
+
+    /* Cache format is little endian.  */
+    cache_file_new_flags_endian_little = 2,
+
+    /* Cache format is big endian.  */
+    cache_file_new_flags_endian_big = 3,
+
+    /* Bit mask to extract the cache_file_new_flags_endian_*
+       values.  */
+    cache_file_new_flags_endian_mask = 3,
+
+    /* Expected value of the endian bits in the flags member for the
+       current architecture.  */
+    cache_file_new_flags_endian_current
+      = (__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+        ? cache_file_new_flags_endian_little
+        : cache_file_new_flags_endian_big),
+  };
+
 struct cache_file_new
 {
   char magic[sizeof CACHEMAGIC_NEW - 1];
   char version[sizeof CACHE_VERSION - 1];
   uint32_t nlibs;              /* Number of entries.  */
   uint32_t len_strings;                /* Size of string table. */
-  uint32_t unused[5];          /* Leave space for future extensions
+
+  /* flags & cache_file_new_flags_endian_mask is one of the values
+     cache_file_new_flags_endian_unset, cache_file_new_flags_endian_invalid,
+     cache_file_new_flags_endian_little, cache_file_new_flags_endian_big.
+
+     The remaining bits are unused and should be generated as zero and
+     ignored by readers.  */
+  uint8_t flags;
+
+  uint8_t padding_unsed[3];    /* Not used, for future extensions.  */
+
+  uint32_t unused[4];          /* Leave space for future extensions
                                   and align to 8 byte boundary.  */
   struct file_entry_new libs[0]; /* Entries describing libraries.  */
   /* After this the string table of size len_strings is found. */
 };
+_Static_assert (sizeof (struct cache_file_new) == 48,
+               "size of struct cache_file_new");
+
+/* Returns false if *CACHE has the wrong endianness for this
+   architecture, and true if the endianness matches (or is
+   unknown).  */
+static inline bool
+cache_file_new_matches_endian (const struct cache_file_new *cache)
+{
+  /* A zero value for cache->flags means that no endianness
+     information is available.  */
+  return cache->flags == 0
+    || ((cache->flags & cache_file_new_flags_endian_big)
+       == cache_file_new_flags_endian_current);
+}
+
 
 /* Used to align cache_file_new.  */
 #define ALIGN_CACHE(addr)                              \
@@ -110,3 +170,5 @@ struct cache_file_new
  & (~(__alignof__ (struct cache_file_new) - 1)))
 
 extern int _dl_cache_libcmp (const char *p1, const char *p2) attribute_hidden;
+
+#endif /* _DL_CACHE_H */