ARRAY_SIZE: check for type

We can use a gcc extension to ensure that ARRAY_SIZE() is handed an array,
not a pointer.  This is especially important when code is changed from a
fixed array to a pointer.  I assume the Intel compiler doesn't support
__builtin_types_compatible_p.

[jdike@addtoit.com: uml: update UML definition of ARRAY_SIZE]
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index 9008eabb9c3d..a9f794716a81 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -22,6 +22,9 @@
     __asm__ ("" : "=r"(__ptr) : "0"(ptr));              \
     (typeof(ptr)) (__ptr + (off)); })
 
+/* &a[0] degrades to a pointer: a different type from an array */
+#define __must_be_array(a) \
+  BUILD_BUG_ON_ZERO(__builtin_types_compatible_p(typeof(a), typeof(&a[0])))
 
 #define inline          inline          __attribute__((always_inline))
 #define __inline__      __inline__      __attribute__((always_inline))