[PATCH v2 2/3] compiler.h: Introduce __must_be_byte_array()

[Kees Cook]

In preparation for adding stricter type checking to the str/mem*()
helpers, provide a way to check that a variable is a byte array
via __must_be_byte_array().

Suggested-by: Kent Overstreet <kent.overstreet@xxxxxxxxx>
Signed-off-by: Kees Cook <kees@xxxxxxxxxx>
---
 include/linux/compiler.h | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 7af999a131cb..1c0688319435 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -221,7 +221,13 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 #endif /* __CHECKER__ */
 
 /* &a[0] degrades to a pointer: a different type from an array */
-#define __must_be_array(a)	__BUILD_BUG_ON_ZERO_MSG(__same_type((a), &(a)[0]), "must be array")
+#define __is_array(a)		(!__same_type((a), &(a)[0]))
+#define __must_be_array(a)	__BUILD_BUG_ON_ZERO_MSG(!__is_array(a), \
+							"must be array")
+
+#define __is_byte_array(a)	(__is_array(a) && sizeof((a)[0]) == 1)
+#define __must_be_byte_array(a)	__BUILD_BUG_ON_ZERO_MSG(!__is_byte_array(a), \
+							"must be byte array")
 
 /* Require C Strings (i.e. NUL-terminated) lack the "nonstring" attribute. */
 #define __must_be_cstr(p) \
-- 
2.34.1