use offsetof macro to make scan-build happy

scan-build from clang version 9 complains about following:

 cache.c:106:2: warning: Dereference of null pointer
        nl_list_for_each_entry_safe(obj, tmp, &cache->c_items, ce_list)
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 include/netlink/list.h:83:20: note: expanded from macro 'nl_list_for_each_entry_safe'
             pos = n, n = nl_list_entry(n->member.next, typeof(*n), member))
                          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 include/netlink/list.h:60:2: note: expanded from macro 'nl_list_entry'
        nl_container_of(ptr, type, member)
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 include/netlink/list.h:56:55: note: expanded from macro 'nl_container_of'
        const typeof( ((type *)0)->member ) *__mptr = (ptr);    \
                                                      ^~~~~

Signed-off-by: Petr Štetiar <ynezz@true.cz>

diff --git a/include/netlink/list.h b/include/netlink/list.h
index c6876a77f76c287cc3fbe37ec7c902ccddd517c0..6eae2160327ae41ae4e60d7a176d73dd5b3974e0 100644 (file)
--- a/include/netlink/list.h
+++ b/include/netlink/list.h
@@ -12,6 +12,8 @@
 #ifndef NETLINK_LIST_H_
 #define NETLINK_LIST_H_
 
+#include <stddef.h>
+
 struct nl_list_head
 {
        struct nl_list_head *   next;
@@ -54,7 +56,7 @@ static inline int nl_list_empty(struct nl_list_head *head)
 
 #define nl_container_of(ptr, type, member) ({                  \
         const typeof( ((type *)0)->member ) *__mptr = (ptr);   \
-        (type *)( (char *)__mptr - ((size_t) &((type *)0)->member));})
+        (type *) ((char *) __mptr - (offsetof(type, member)));})
 
 #define nl_list_entry(ptr, type, member) \
        nl_container_of(ptr, type, member)