[Xen-changelog] [xen-unstable] Fix BUILD_BUG_ON()

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1228994341 0
# Node ID 1419a73316e1d75d3e5d7c1530ac6ae7e7bc7fb4
# Parent  6401c9533ef52e9217b39fa7f07df97e757683bc
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@xxxxxxxxxx>
---
 xen/include/xen/lib.h |    2 +-
 1 files changed, 1 insertion(+), 1 deletion(-)

diff -r 6401c9533ef5 -r 1419a73316e1 xen/include/xen/lib.h
--- a/xen/include/xen/lib.h     Wed Dec 10 14:05:41 2008 +0000
+++ b/xen/include/xen/lib.h     Thu Dec 11 11:19:01 2008 +0000
@@ -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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