Fix BUILD_BUG_ON()

As was noticed on the Linux side, using an array here isn't
appropriate
if the condition is not a compile time constant - gcc allows such
arrays, and hence the intended effect of producing a compiler error is
not achieved in that case. Bit field widths do not know similar
language extensions, and hence always produce a compiler error.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
xen-unstable changeset:   18899:1419a73316e1d75d3e5d7c1530ac6ae7e7bc7fb4
xen-unstable date:        Thu Dec 11 11:19:01 2008 +0000

diff --git a/xen/include/xen/lib.h b/xen/include/xen/lib.h
index d6aa891eb944b178d366c47af23a952c61b65f4d..cbadd0de1520afaccd145d04809ec8b6c8fdeef7 100644 (file)
--- a/xen/include/xen/lib.h
+++ b/xen/include/xen/lib.h
@@ -16,7 +16,7 @@ void __warn(char *file, int line);
 #define WARN_ON(p) do { if (p) WARN(); } while (0)
 
 /* Force a compilation error if condition is true */
-#define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2 * !!(condition)]))
+#define BUILD_BUG_ON(condition) ((void)sizeof(struct { int:-!!(condition); }))
 
 #ifndef assert_failed
 #define assert_failed(p)                                        \