Introduce __must_be_array

Cloning the similar construct from Linux, allowing to detect improper
uses of ARRAY_SIZE() at build time.

Signed-off-by: Jan Beulich <jbeulich@novell.com>

diff --git a/xen/include/xen/compiler.h b/xen/include/xen/compiler.h
index 95295dce76ae63e16af5e553bd9a1bdcd4705d43..909dec0bdfb71ef0cc207eff1e3bf25ac9e773ec 100644 (file)
--- a/xen/include/xen/compiler.h
+++ b/xen/include/xen/compiler.h
@@ -35,6 +35,10 @@
 #define offsetof(a,b) ((unsigned long)&(((a *)0)->b))
 #endif
 
+/* &a[0] degrades to a pointer: a different type from an array */
+#define __must_be_array(a) \
+  BUILD_BUG_ON_ZERO(__builtin_types_compatible_p(typeof(a), typeof(&a[0])))
+
 #ifdef GCC_HAS_VISIBILITY_ATTRIBUTE
 /* Results in more efficient PIC code (no indirections through GOT or PLT). */
 #pragma GCC visibility push(hidden)

diff --git a/xen/include/xen/config.h b/xen/include/xen/config.h
index b459e80313c5a46e9a9139089215415b4d5da2f6..9b26d882bb8c23a5aff65c2f96776f0764a1ab90 100644 (file)
--- a/xen/include/xen/config.h
+++ b/xen/include/xen/config.h
@@ -11,7 +11,7 @@
 
 #define EXPORT_SYMBOL(var)
 #define EXPORT_SYMBOL_GPL(var)
-#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]) + __must_be_array(x))
 
 /*
  * The following log levels are as follows:

diff --git a/xen/include/xen/lib.h b/xen/include/xen/lib.h
index f5c21f64f75894953238a377fd509e237a7b62c4..ab76120da68f6340fa8767b6de10add60a311ae5 100644 (file)
--- a/xen/include/xen/lib.h
+++ b/xen/include/xen/lib.h
@@ -18,6 +18,12 @@ void __warn(char *file, int line);
 /* Force a compilation error if condition is true */
 #define BUILD_BUG_ON(condition) ((void)sizeof(struct { int:-!!(condition); }))
 
+/* Force a compilation error if condition is true, but also produce a
+   result (of value 0 and type size_t), so the expression can be used
+   e.g. in a structure initializer (or where-ever else comma expressions
+   aren't permitted). */
+#define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:-!!(e); }))
+
 #ifndef assert_failed
 #define assert_failed(p)                                        \
 do {                                                            \