util: Avoid uninitialized pointer complaints from Coverity.

diff --git a/lib/util.h b/lib/util.h
index 635d331..e533987 100644 (file)
--- a/lib/util.h
+++ b/lib/util.h
@@ -85,6 +85,22 @@ extern const char *program_name;
 #define OVS_TYPEOF(OBJECT) void *
 #endif
 
+/* Given OBJECT of type pointer-to-structure, expands to the offset of MEMBER
+ * within an instance of the structure.
+ *
+ * The GCC-specific version avoids the technicality of undefined behavior if
+ * OBJECT is null, invalid, or not yet initialized.  This makes some static
+ * checkers (like Coverity) happier.  But the non-GCC version does not actually
+ * dereference any pointer, so it would be surprising for it to cause any
+ * problems in practice.
+ */
+#ifdef __GNUC__
+#define OBJECT_OFFSETOF(OBJECT, MEMBER) offsetof(typeof(*(OBJECT)), MEMBER)
+#else
+#define OBJECT_OFFSETOF(OBJECT, MEMBER) \
+    ((char *) &(OBJECT)->MEMBER - (char *) (OBJECT))
+#endif
+
 /* Given POINTER, the address of the given MEMBER in a STRUCT object, returns
    the STRUCT object. */
 #define CONTAINER_OF(POINTER, STRUCT, MEMBER)                           \
@@ -99,7 +115,7 @@ extern const char *program_name;
  * from the type of '*OBJECT'. */
 #define OBJECT_CONTAINING(POINTER, OBJECT, MEMBER)                      \
     ((OVS_TYPEOF(OBJECT)) (void *)                                      \
-     ((char *) (POINTER) - ((char *) &(OBJECT)->MEMBER - (char *) (OBJECT))))
+     ((char *) (POINTER) - OBJECT_OFFSETOF(OBJECT, MEMBER)))
 
 /* Given POINTER, the address of the given MEMBER within an object of the type
  * that that OBJECT points to, assigns the address of the outer object to