Add macro to safely derive the size of an array
diff --git a/libkmod/macro.h b/libkmod/macro.h
index 11e38a7..d09d664 100644
--- a/libkmod/macro.h
+++ b/libkmod/macro.h
@@ -48,6 +48,29 @@
((char *)(member_ptr) - offsetof(containing_type, member)) \
- check_types_match(*(member_ptr), ((containing_type *)0)->member))
+/**
+ * BUILD_ASSERT_OR_ZERO - assert a build-time dependency, as an expression.
+ * @cond: the compile-time condition which must be true.
+ *
+ * Your compile will fail if the condition isn't true, or can't be evaluated
+ * by the compiler. This can be used in an expression: its value is "0".
+ *
+ * Example:
+ * #define foo_to_char(foo) \
+ * ((char *)(foo) \
+ * + BUILD_ASSERT_OR_ZERO(offsetof(struct foo, string) == 0))
+ */
+#define BUILD_ASSERT_OR_ZERO(cond) \
+ (sizeof(char [1 - 2*!(cond)]) - 1)
+
+/* Two gcc extensions.
+ * &a[0] degrades to a pointer: a different type from an array */
+#define _array_size_chk(arr) \
+ BUILD_ASSERT_OR_ZERO(!__builtin_types_compatible_p(typeof(arr), \
+ typeof(&(arr)[0])))
+
+#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) + _array_size_chk(arr))
+
/* Attributes */
#define __must_check __attribute__((warn_unused_result))