kernel.h: Add BUILD_BUG() macro.

We can place this in definitions that we expect the compiler to remove
by dead code elimination.  If this assertion fails, we get a nice
error message at build time.

The GCC function attribute error("message") was added in version 4.3,
so we define a new macro __linktime_error(message) to expand to this
for GCC-4.3 and later.  This will give us an error diagnostic from the
compiler on the line that fails.  For other compilers
__linktime_error(message) expands to nothing, and we have to be
content with a link time error, but at least we will still get a build
error.

BUILD_BUG() expands to the undefined function __build_bug_failed() and
will fail at link time if the compiler ever emits code for it.  On
GCC-4.3 and later, attribute((error())) is used so that the failure
will be noted at compile time instead.

Acked-by: David Howells <dhowells@redhat.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: David Daney <david.daney@cavium.com>
Cc: David Rientjes <rientjes@google.com>
Cc: DM <dm.n9107@gmail.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 34ce1102b1c796ba7ef10aca83b328b1d89b130b..d0a7a0c7166101e266a3008e65fd89969ab3b8a2 100644 (file)
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -710,7 +710,7 @@ extern int __build_bug_on_failed;
  * BUILD_BUG - break compile if used.
  *
  * If you have some code that you expect the compiler to eliminate at
- * build time, you should use BUILD_BUG_ON_USED to detect if it is
+ * build time, you should use BUILD_BUG to detect if it is
  * unexpectedly used.
  */
 #define BUILD_BUG()                                            \