forked from rpms/glibc
313 lines
10 KiB
Diff
313 lines
10 KiB
Diff
commit dfb3f101c5ef23adf60d389058a2b33e23303d04
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Author: Florian Weimer <fweimer@redhat.com>
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Date: Fri Dec 4 09:13:43 2020 +0100
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elf: Add extension mechanism to ld.so.cache
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A previously unused new-format header field is used to record
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the address of an extension directory.
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This change adds a demo extension which records the version of
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ldconfig which builds a file.
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Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
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diff --git a/elf/cache.c b/elf/cache.c
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index 28e4889d006d2f0b..5a8f1ad70cc3fead 100644
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--- a/elf/cache.c
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+++ b/elf/cache.c
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@@ -15,6 +15,7 @@
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You should have received a copy of the GNU General Public License
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along with this program; if not, see <http://www.gnu.org/licenses/>. */
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+#include <assert.h>
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#include <errno.h>
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#include <error.h>
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#include <dirent.h>
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@@ -33,6 +34,7 @@
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#include <ldconfig.h>
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#include <dl-cache.h>
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+#include <version.h>
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struct cache_entry
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{
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@@ -161,6 +163,21 @@ check_new_cache (struct cache_file_new *cache)
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error (EXIT_FAILURE, 0, _("Cache file has wrong endianness.\n"));
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}
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+/* Print the extension information at the cache at start address
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+ FILE_BASE, of length FILE_SIZE bytes. The new-format cache header
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+ is at CACHE, and the file name for diagnostics is CACHE_NAME. */
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+static void
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+print_extensions (struct cache_extension_all_loaded *ext)
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+{
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+ if (ext->sections[cache_extension_tag_generator].base != NULL)
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+ {
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+ fputs (_("Cache generated by: "), stdout);
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+ fwrite (ext->sections[cache_extension_tag_generator].base, 1,
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+ ext->sections[cache_extension_tag_generator].size, stdout);
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+ putchar ('\n');
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+ }
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+}
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+
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/* Print the whole cache file, if a file contains the new cache format
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hidden in the old one, print the contents of the new format. */
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void
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@@ -250,6 +267,11 @@ print_cache (const char *cache_name)
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}
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else if (format == 1)
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{
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+ struct cache_extension_all_loaded ext;
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+ if (!cache_extension_load (cache_new, cache, cache_size, &ext))
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+ error (EXIT_FAILURE, 0,
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+ _("Malformed extension data in cache file %s\n"), cache_name);
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+
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printf (_("%d libs found in cache `%s'\n"),
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cache_new->nlibs, cache_name);
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@@ -260,6 +282,7 @@ print_cache (const char *cache_name)
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cache_new->libs[i].osversion,
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cache_new->libs[i].hwcap,
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cache_data + cache_new->libs[i].value);
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+ print_extensions (&ext);
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}
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/* Cleanup. */
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munmap (cache, cache_size);
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@@ -301,6 +324,45 @@ compare (const struct cache_entry *e1, const struct cache_entry *e2)
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return res;
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}
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+/* Size of the cache extension directory. All tags are assumed to be
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+ present. */
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+enum
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+ {
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+ cache_extension_size = (offsetof (struct cache_extension, sections)
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+ + (cache_extension_count
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+ * sizeof (struct cache_extension_section)))
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+ };
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+
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+/* Write the cache extensions to FD. The extension directory is
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+ assumed to be located at CACHE_EXTENSION_OFFSET. */
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+static void
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+write_extensions (int fd, uint32_t cache_extension_offset)
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+{
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+ assert ((cache_extension_offset % 4) == 0);
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+
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+ struct cache_extension *ext = xmalloc (cache_extension_size);
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+ ext->magic = cache_extension_magic;
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+ ext->count = cache_extension_count;
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+
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+ for (int i = 0; i < cache_extension_count; ++i)
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+ {
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+ ext->sections[i].tag = i;
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+ ext->sections[i].flags = 0;
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+ }
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+
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+ const char *generator
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+ = "ldconfig " PKGVERSION RELEASE " release version " VERSION;
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+ ext->sections[cache_extension_tag_generator].offset
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+ = cache_extension_offset + cache_extension_size;
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+ ext->sections[cache_extension_tag_generator].size = strlen (generator);
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+
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+ if (write (fd, ext, cache_extension_size) != cache_extension_size
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+ || write (fd, generator, strlen (generator)) != strlen (generator))
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+ error (EXIT_FAILURE, errno, _("Writing of cache extension data failed"));
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+
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+ free (ext);
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+}
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+
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/* Save the contents of the cache. */
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void
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save_cache (const char *cache_name)
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@@ -435,6 +497,25 @@ save_cache (const char *cache_name)
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&& idx_old < cache_entry_old_count)
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file_entries->libs[idx_old] = file_entries->libs[idx_old - 1];
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+ /* Compute the location of the extension directory. This
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+ implementation puts the directory after the string table. The
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+ size computation matches the write calls below. The extension
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+ directory does not exist with format 0, so the value does not
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+ matter. */
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+ uint32_t extension_offset = 0;
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+ if (opt_format != opt_format_new)
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+ extension_offset += file_entries_size;
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+ if (opt_format != opt_format_old)
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+ {
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+ if (opt_format != opt_format_new)
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+ extension_offset += pad;
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+ extension_offset += file_entries_new_size;
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+ }
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+ extension_offset += total_strlen;
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+ extension_offset = roundup (extension_offset, 4); /* Provide alignment. */
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+ if (opt_format != opt_format_old)
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+ file_entries_new->extension_offset = extension_offset;
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+
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/* Write out the cache. */
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/* Write cache first to a temporary file and rename it later. */
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@@ -473,6 +554,14 @@ save_cache (const char *cache_name)
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if (write (fd, strings, total_strlen) != (ssize_t) total_strlen)
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error (EXIT_FAILURE, errno, _("Writing of cache data failed"));
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+ if (opt_format != opt_format_old)
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+ {
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+ /* Align file position to 4. */
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+ off64_t old_offset = lseek64 (fd, extension_offset, SEEK_SET);
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+ assert ((unsigned long long int) (extension_offset - old_offset) < 4);
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+ write_extensions (fd, extension_offset);
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+ }
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+
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/* Make sure user can always read cache file */
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if (chmod (temp_name, S_IROTH|S_IRGRP|S_IRUSR|S_IWUSR))
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error (EXIT_FAILURE, errno,
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diff --git a/sysdeps/generic/dl-cache.h b/sysdeps/generic/dl-cache.h
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index 6ecfd6da0e59329c..259e843724531630 100644
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--- a/sysdeps/generic/dl-cache.h
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+++ b/sysdeps/generic/dl-cache.h
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@@ -21,7 +21,9 @@
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#include <endian.h>
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#include <stdbool.h>
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+#include <stddef.h>
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#include <stdint.h>
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+#include <string.h>
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#ifndef _DL_CACHE_DEFAULT_ID
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# define _DL_CACHE_DEFAULT_ID 3
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@@ -142,7 +144,11 @@ struct cache_file_new
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uint8_t padding_unsed[3]; /* Not used, for future extensions. */
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- uint32_t unused[4]; /* Leave space for future extensions
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+ /* File offset of the extension directory. See struct
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+ cache_extension below. Must be a multiple of four. */
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+ uint32_t extension_offset;
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+
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+ uint32_t unused[3]; /* Leave space for future extensions
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and align to 8 byte boundary. */
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struct file_entry_new libs[0]; /* Entries describing libraries. */
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/* After this the string table of size len_strings is found. */
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@@ -164,6 +170,121 @@ cache_file_new_matches_endian (const struct cache_file_new *cache)
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}
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+/* Randomly chosen magic value, which allows for additional
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+ consistency verification. */
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+enum { cache_extension_magic = (uint32_t) -358342284 };
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+
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+/* Tag values for different kinds of extension sections. Similar to
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+ SHT_* constants. */
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+enum cache_extension_tag
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+ {
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+ /* Array of bytes containing the glibc version that generated this
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+ cache file. */
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+ cache_extension_tag_generator,
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+
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+ /* Total number of known cache extension tags. */
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+ cache_extension_count
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+ };
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+
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+/* Element in the array following struct cache_extension. Similar to
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+ an ELF section header. */
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+struct cache_extension_section
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+{
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+ /* Type of the extension section. A enum cache_extension_tag value. */
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+ uint32_t tag;
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+
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+ /* Extension-specific flags. Currently generated as zero. */
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+ uint32_t flags;
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+
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+ /* Offset from the start of the file for the data in this extension
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+ section. Specific extensions can have alignment constraints. */
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+ uint32_t offset;
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+
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+ /* Length in bytes of the extension data. Specific extensions may
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+ have size requirements. */
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+ uint32_t size;
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+};
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+
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+/* The extension directory in the cache. An array of struct
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+ cache_extension_section entries. */
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+struct cache_extension
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+{
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+ uint32_t magic; /* Always cache_extension_magic. */
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+ uint32_t count; /* Number of following entries. */
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+
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+ /* count section descriptors of type struct cache_extension_section
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+ follow. */
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+ struct cache_extension_section sections[];
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+};
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+
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+/* A relocated version of struct cache_extension_section. */
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+struct cache_extension_loaded
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+{
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+ /* Address and size of this extension section. base is NULL if the
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+ section is missing from the file. */
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+ const void *base;
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+ size_t size;
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+
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+ /* Flags from struct cache_extension_section. */
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+ uint32_t flags;
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+};
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+
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+/* All supported extension sections, relocated. Filled in by
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+ cache_extension_load below. */
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+struct cache_extension_all_loaded
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+{
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+ struct cache_extension_loaded sections[cache_extension_count];
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+};
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+
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+static bool __attribute__ ((unused))
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+cache_extension_load (const struct cache_file_new *cache,
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+ const void *file_base, size_t file_size,
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+ struct cache_extension_all_loaded *loaded)
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+{
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+ memset (loaded, 0, sizeof (*loaded));
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+ if (cache->extension_offset == 0)
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+ /* No extensions present. This is not a format error. */
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+ return true;
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+ if ((cache->extension_offset % 4) != 0)
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+ /* Extension offset is misaligned. */
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+ return false;
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+ size_t size_tmp;
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+ if (__builtin_add_overflow (cache->extension_offset,
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+ sizeof (struct cache_extension), &size_tmp)
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+ || size_tmp > file_size)
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+ /* Extension extends beyond the end of the file. */
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+ return false;
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+ const struct cache_extension *ext = file_base + cache->extension_offset;
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+ if (ext->magic != cache_extension_magic)
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+ return false;
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+ if (__builtin_mul_overflow (ext->count,
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+ sizeof (struct cache_extension_section),
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+ &size_tmp)
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+ || __builtin_add_overflow (cache->extension_offset
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+ + sizeof (struct cache_extension), size_tmp,
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+ &size_tmp)
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+ || size_tmp > file_size)
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+ /* Extension array extends beyond the end of the file. */
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+ return false;
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+ for (uint32_t i = 0; i < ext->count; ++i)
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+ {
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+ if (__builtin_add_overflow (ext->sections[i].offset,
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+ ext->sections[i].size, &size_tmp)
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+ || size_tmp > file_size)
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+ /* Extension data extends beyond the end of the file. */
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+ return false;
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+
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+ uint32_t tag = ext->sections[i].tag;
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+ if (tag >= cache_extension_count)
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+ /* Tag is out of range and unrecognized. */
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+ continue;
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+ loaded->sections[tag].base = file_base + ext->sections[i].offset;
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+ loaded->sections[tag].size = ext->sections[i].size;
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+ loaded->sections[tag].flags = ext->sections[i].flags;
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+ }
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+ return true;
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+}
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+
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/* Used to align cache_file_new. */
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#define ALIGN_CACHE(addr) \
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(((addr) + __alignof__ (struct cache_file_new) -1) \
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