[PATCH v10 3/9] compiler_types.h: Add assert_type to catch type mis-match while compiling

[Gwan-gyeong Mun]

It adds assert_type and assert_typable macros to catch type mis-match while
compiling. The existing typecheck() macro outputs build warnings, but the
newly added assert_type() macro uses the _Static_assert() keyword (which is
introduced in C11) to generate a build break when the types are different
and can be used to detect explicit build errors.
Unlike the assert_type() macro, assert_typable() macro allows a constant
value as the second argument.

Suggested-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@xxxxxxxxx>
Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
Cc: Matthew Auld <matthew.auld@xxxxxxxxx>
Cc: Nirmoy Das <nirmoy.das@xxxxxxxxx>
Cc: Jani Nikula <jani.nikula@xxxxxxxxx>
Cc: Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx>
Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
Cc: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
---
 include/linux/compiler_types.h | 39 ++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index 4f2a819fd60a..19cc125918bb 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -294,6 +294,45 @@ struct ftrace_likely_data {
 /* Are two types/vars the same type (ignoring qualifiers)? */
 #define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))
 
+/**
+ * assert_type - break compile if the first argument's data type and the second
+ *               argument's data type are not the same
+ *
+ * @t1: data type or variable
+ * @t2: data type or variable
+ *
+ * The first and second arguments can be data types or variables or mixed (the
+ * first argument is the data type and the second argument is variable or vice
+ * versa). It determines whether the first argument's data type and the second
+ * argument's data type are the same while compiling, and it breaks compile if
+ * the two types are not the same.
+ * See also assert_typable().
+ */
+#define assert_type(t1, t2) _Static_assert(__same_type(t1, t2))
+
+/**
+ * assert_typable - break compile if the first argument's data type and the
+ *                  second argument's data type are not the same
+ *
+ * @t: data type or variable
+ * @n: data type or variable or constant value
+ *
+ * The first and second arguments can be data types or variables or mixed (the
+ * first argument is the data type and the second argument is variable or vice
+ * versa). Unlike the assert_type() macro, this macro allows a constant value
+ * as the second argument. And if the second argument is a constant value, it
+ * always passes. And it doesn't mean that the types are explicitly the same.
+ * When a constant value is used as the second argument, if you need an
+ * overflow check when assigning a constant value to a variable of the type of
+ * the first argument, you can use the overflows_type() macro. When a constant
+ * value is not used as a second argument, it determines whether the first
+ * argument's data type and the second argument's data type are the same while
+ * compiling, and it breaks compile if the two types are not the same.
+ * See also assert_type() and overflows_type().
+ */
+#define assert_typable(t, n) _Static_assert(__builtin_constant_p(n) ||	\
+					    __same_type(t, typeof(n)))
+
 /*
  * __unqual_scalar_typeof(x) - Declare an unqualified scalar type, leaving
  *			       non-scalar types unchanged.
-- 
2.37.1