{
        struct object *obj = &blob->object;
 
+       if (!blob)
+               die("bad blob object");
        if (obj->flags & SEEN)
                return;
        obj->flags |= SEEN;
        struct name_entry entry;
        struct name_path me;
 
+       if (!tree)
+               die("bad tree object");
        if (obj->flags & SEEN)
                return;
        obj->flags |= SEEN;
 
        if (parse_tag(tag) < 0)
                die("bad tag object %s", sha1_to_hex(obj->sha1));
-       add_object(tag->tagged, p, NULL, name);
+       if (tag->tagged)
+               add_object(tag->tagged, p, NULL, name);
 }
 
 static void walk_commit_list(struct rev_info *revs)
                 * lookup_blob() on them, to avoid populating the hash table
                 * with invalid information
                 */
-               if (S_ISGITLINK(ntohl(active_cache[i]->ce_mode)))
+               if (S_ISGITLINK(active_cache[i]->ce_mode))
                        continue;
 
                lookup_blob(active_cache[i]->sha1);
         * Set up the revision walk - this will move all commits
         * from the pending list to the commit walking list.
         */
-       prepare_revision_walk(revs);
+       if (prepare_revision_walk(revs))
+               die("revision walk setup failed");
        walk_commit_list(revs);
 }