[Xen-devel] [PATCH] change BUILD_BUG_ON()

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

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@xxxxxxxxxx>

--- 2008-11-20.orig/xen/include/xen/lib.h       2007-09-10 09:59:38.000000000 
+0200
+++ 2008-11-20/xen/include/xen/lib.h    2008-12-11 09:54:51.000000000 +0100
@@ -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)                                        \




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