[Qemu-devel] [PATCH v2 4/4] ARRAY_SIZE: check that argument is an array

[Michael S. Tsirkin]

It's a familiar pattern: some code uses ARRAY_SIZE, then refactoring
changes the argument from an array to a pointer to a dynamically
allocated buffer.  Code keeps compiling but any ARRAY_SIZE calls now
return the size of the pointer divided by element size.

Let's add build time checks to ARRAY_SIZE before we allow more
of these in the code-base.

Signed-off-by: Michael S. Tsirkin <address@hidden>
---
 include/qemu/osdep.h | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index 689f253..24bfda0 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -199,7 +199,13 @@ extern int daemon(int, int);
 #endif
 
 #ifndef ARRAY_SIZE
-#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+/*
+ * &(x)[0] is always a pointer - if it's same type as x then the argument is a
+ * pointer, not an array as expected.
+ */
+#define ARRAY_SIZE(x) ((sizeof(x) / sizeof((x)[0])) + QEMU_BUILD_BUG_ON_ZERO( \
+                        __builtin_types_compatible_p(typeof(x), \
+                                                     typeof(&(x)[0]))))
 #endif
 
 int qemu_daemon(int nochdir, int noclose);
-- 
MST