[Xen-devel] [PATCH] introduce __must_be_array

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

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

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

--- 2009-03-27.orig/xen/include/xen/compiler.h  2008-06-10 18:00:41.000000000 
+0200
+++ 2009-03-27/xen/include/xen/compiler.h       2009-04-07 13:38:22.000000000 
+0200
@@ -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)
--- 2009-03-27.orig/xen/include/xen/config.h    2007-10-12 16:12:16.000000000 
+0200
+++ 2009-03-27/xen/include/xen/config.h 2009-04-07 13:41:00.000000000 +0200
@@ -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:
--- 2009-03-27.orig/xen/include/xen/lib.h       2009-03-30 09:11:46.000000000 
+0200
+++ 2009-03-27/xen/include/xen/lib.h    2009-04-07 13:43:03.000000000 +0200
@@ -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 {                                                            \




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