BUILD_BUG_ON: make it handle more cases

[mv-sheeva.git] / include / linux / kernel.h

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index d07d8057e440e9eb685b0ab36d9f29cd64db97d5..864712f3653d5804a08ca428f61f6eaf124da407 100644 (file)
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -575,12 +575,6 @@ struct sysinfo {
        char _f[20-2*sizeof(long)-sizeof(int)]; /* Padding: libc5 uses this.. */
 };
 
-/* Force a compilation error if condition is true */
-#define BUILD_BUG_ON(condition) ((void)BUILD_BUG_ON_ZERO(condition))
-
-/* Force a compilation error if condition is constant and true */
-#define MAYBE_BUILD_BUG_ON(cond) ((void)sizeof(char[1 - 2 * !!(cond)]))
-
 /* Force a compilation error if a constant expression is not a power of 2 */
 #define BUILD_BUG_ON_NOT_POWER_OF_2(n)                 \
        BUILD_BUG_ON((n) == 0 || (((n) & ((n) - 1)) != 0))
@@ -592,6 +586,33 @@ struct sysinfo {
 #define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:-!!(e); }))
 #define BUILD_BUG_ON_NULL(e) ((void *)sizeof(struct { int:-!!(e); }))
 
+/**
+ * BUILD_BUG_ON - break compile if a condition is true.
+ * @cond: the condition which the compiler should know is false.
+ *
+ * If you have some code which relies on certain constants being equal, or
+ * other compile-time-evaluated condition, you should use BUILD_BUG_ON to
+ * detect if someone changes it.
+ *
+ * The implementation uses gcc's reluctance to create a negative array, but
+ * gcc (as of 4.4) only emits that error for obvious cases (eg. not arguments
+ * to inline functions).  So as a fallback we use the optimizer; if it can't
+ * prove the condition is false, it will cause a link error on the undefined
+ * "__build_bug_on_failed".  This error message can be harder to track down
+ * though, hence the two different methods.
+ */
+#ifndef __OPTIMIZE__
+#define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
+#else
+extern int __build_bug_on_failed;
+#define BUILD_BUG_ON(condition)                                        \
+       do {                                                    \
+               ((void)sizeof(char[1 - 2*!!(condition)]));      \
+               if (condition) __build_bug_on_failed = 1;       \
+       } while(0)
+#endif
+#define MAYBE_BUILD_BUG_ON(condition) BUILD_BUG_ON(condition)
+
 /* Trap pasters of __FUNCTION__ at compile-time */
 #define __FUNCTION__ (__func__)