[PATCH v7 2/8] util_macros: Add exact_type macro to catch type mis-match while compiling

Gwan-gyeong Mun
2022-08-16T10:15:03Z

It adds exact_type and exactly_pgoff_t macro to catch type mis-match while
compiling. The existing typecheck() macro outputs build warnings, but the
newly added exact_type() macro uses the BUILD_BUG_ON() macro to generate
a build break when the types are different and can be used to detect
explicit build errors.

v6: Move macro addition location so that it can be used by other than drm
subsystem (Jani, Mauro, Andi)

Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Nirmoy Das <nirmoy.das@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Andi Shyti <andi.shyti@linux.intel.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
---
include/linux/util_macros.h | 25 +++++++++++++++++++++++++
1 file changed, 25 insertions(+)

diff --git a/include/linux/util_macros.h b/include/linux/util_macros.h
index 72299f261b25..b6624b275257 100644
--- a/include/linux/util_macros.h
+++ b/include/linux/util_macros.h
@@ -2,6 +2,9 @@
#ifndef _LINUX_HELPER_MACROS_H_
#define _LINUX_HELPER_MACROS_H_

+#include <linux/types.h>
+#include <linux/bug.h>
+
#define __find_closest(x, a, as, op) \
({ \
typeof(as) __fc_i, __fc_as = (as) - 1; \
@@ -38,4 +41,26 @@
*/
#define find_closest_descending(x, a, as) __find_closest(x, a, as, >=)

+/**
+ * exact_type - break compile if source type and destination value's type are
+ * not the same
+ * @T: Source type
+ * @n: Destination value
+ *
+ * It is a helper macro for a poor man's -Wconversion: only allow variables of
+ * an exact type. It determines whether the source type and destination value's
+ * type are the same while compiling, and it breaks compile if two types are
+ * not the same
+ */
+#define exact_type(T, n) \
+ BUILD_BUG_ON(!__builtin_constant_p(n) && !__builtin_types_compatible_p(T, typeof(n)))
+
+/**
+ * exactly_pgoff_t - helper to check if the type of a value is pgoff_t
+ * @n: value to compare pgoff_t type
+ *
+ * It breaks compile if the argument value's type is not pgoff_t type.
+ */
+#define exactly_pgoff_t(n) exact_type(pgoff_t, n)
+
#endif
--
2.37.1