commit 84ba719b260551918965d0a433914de683087645
Author: Florian Weimer <fweimer@redhat.com>
Date: Fri Dec 4 09:13:43 2020 +0100
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 edcdd4b7cc1a6a0b..28e4889d006d2f0b 100644
--- 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 366a051dfcd26132..de063faa8b2c88ae 100644
--- 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 3c5730dfe42c7c88..6ecfd6da0e59329c 100644
--- 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
<http://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 */