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.
Signed-off-by: David Daney <david.daney@cavium.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: DM <dm.n9107@gmail.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/compiler-gcc4.h b/include/linux/compiler-gcc4.h
index dfadc96..2f40791 100644
--- a/include/linux/compiler-gcc4.h
+++ b/include/linux/compiler-gcc4.h
@@ -29,6 +29,7 @@
the kernel context */
#define __cold __attribute__((__cold__))
+#define __linktime_error(message) __attribute__((__error__(message)))
#if __GNUC_MINOR__ >= 5
/*
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 320d6c9..4a24354 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -293,7 +293,9 @@
#ifndef __compiletime_error
# define __compiletime_error(message)
#endif
-
+#ifndef __linktime_error
+# define __linktime_error(message)
+#endif
/*
* Prevent the compiler from merging or refetching accesses. The compiler
* is also forbidden from reordering successive instances of ACCESS_ONCE(),
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index e8b1597..f48e8a5 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -665,6 +665,7 @@
#define BUILD_BUG_ON_ZERO(e) (0)
#define BUILD_BUG_ON_NULL(e) ((void*)0)
#define BUILD_BUG_ON(condition)
+#define BUILD_BUG() (0)
#else /* __CHECKER__ */
/* Force a compilation error if a constant expression is not a power of 2 */
@@ -703,6 +704,21 @@
if (condition) __build_bug_on_failed = 1; \
} while(0)
#endif
+
+/**
+ * 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 to detect if it is
+ * unexpectedly used.
+ */
+#define BUILD_BUG() \
+ do { \
+ extern void __build_bug_failed(void) \
+ __linktime_error("BUILD_BUG failed"); \
+ __build_bug_failed(); \
+ } while (0)
+
#endif /* __CHECKER__ */
/* Trap pasters of __FUNCTION__ at compile-time */