[PATCH v6 1/8] overflow: Move and add few utility macros into overflow

[Gwan-gyeong Mun]

It moves overflows_type utility macro into overflow header from i915_utils
header. The overflows_type can be used to catch the truncation between data
types. And it adds safe_conversion() macro which performs a type conversion
(cast) of an source value into a new variable, checking that the
destination is large enough to hold the source value. And the functionality
of overflows_type has been improved to handle the signbit.
The is_unsigned_type macro has been added to check the sign bit of the
built-in type.

v3: Add is_type_unsigned() macro (Mauro)
    Modify overflows_type() macro to consider signed data types (Mauro)
    Fix the problem that safe_conversion() macro always returns true
v4: Fix kernel-doc markups
v6: Move macro addition location so that it can be used by other than drm
    subsystem (Jani, Mauro, Andi)
    Change is_type_unsigned to is_unsigned_type to have the same name form
    as is_signed_type macro

Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun at intel.com>
Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
Cc: Matthew Auld <matthew.auld at intel.com>
Cc: Nirmoy Das <nirmoy.das at intel.com>
Cc: Jani Nikula <jani.nikula at intel.com>
Cc: Andi Shyti <andi.shyti at linux.intel.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab at kernel.org> (v5)
---
 drivers/gpu/drm/i915/i915_utils.h |  5 +--
 include/linux/overflow.h          | 54 +++++++++++++++++++++++++++++++
 2 files changed, 55 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_utils.h b/drivers/gpu/drm/i915/i915_utils.h
index c10d68cdc3ca..eb0ded23fa9c 100644
--- a/drivers/gpu/drm/i915/i915_utils.h
+++ b/drivers/gpu/drm/i915/i915_utils.h
@@ -32,6 +32,7 @@
 #include <linux/types.h>
 #include <linux/workqueue.h>
 #include <linux/sched/clock.h>
+#include <linux/overflow.h>
 
 #ifdef CONFIG_X86
 #include <asm/hypervisor.h>
@@ -111,10 +112,6 @@ bool i915_error_injected(void);
 #define range_overflows_end_t(type, start, size, max) \
 	range_overflows_end((type)(start), (type)(size), (type)(max))
 
-/* Note we don't consider signbits :| */
-#define overflows_type(x, T) \
-	(sizeof(x) > sizeof(T) && (x) >> BITS_PER_TYPE(T))
-
 #define ptr_mask_bits(ptr, n) ({					\
 	unsigned long __v = (unsigned long)(ptr);			\
 	(typeof(ptr))(__v & -BIT(n));					\
diff --git a/include/linux/overflow.h b/include/linux/overflow.h
index f1221d11f8e5..462a03454377 100644
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h
@@ -35,6 +35,60 @@
 #define type_max(T) ((T)((__type_half_max(T) - 1) + __type_half_max(T)))
 #define type_min(T) ((T)((T)-type_max(T)-(T)1))
 
+/**
+ * is_unsigned_type - helper for checking data type which is an unsigned data
+ * type or not
+ * @x: The data type to check
+ *
+ * Returns:
+ * True if the data type is an unsigned data type, false otherwise.
+ */
+#define is_unsigned_type(x) ((typeof(x))-1 >= (typeof(x))0)
+
+/**
+ * overflows_type - helper for checking the truncation between data types
+ * @x: Source for overflow type comparison
+ * @T: Destination for overflow type comparison
+ *
+ * It compares the values and size of each data type between the first and
+ * second argument to check whether truncation can occur when assigning the
+ * first argument to the variable of the second argument.
+ * Source and Destination can be used with or without sign bit.
+ * Composite data structures such as union and structure are not considered.
+ * Enum data types are not considered.
+ * Floating point data types are not considered.
+ *
+ * Returns:
+ * True if truncation can occur, false otherwise.
+ */
+#define overflows_type(x, T) \
+	(is_unsigned_type(x) ? \
+		is_unsigned_type(T) ? \
+			(sizeof(x) > sizeof(T) && (x) >> BITS_PER_TYPE(T)) ? 1 : 0 \
+			: (sizeof(x) >= sizeof(T) && (x) >> (BITS_PER_TYPE(T) - 1)) ? 1 : 0 \
+	: is_unsigned_type(T) ? \
+		((x) < 0) ? 1 : (sizeof(x) > sizeof(T) && (x) >> BITS_PER_TYPE(T)) ? 1 : 0 \
+		: (sizeof(x) > sizeof(T)) ? \
+			((x) < 0) ? (((x) * -1) >> BITS_PER_TYPE(T)) ? 1 : 0 \
+				: ((x) >> BITS_PER_TYPE(T)) ? 1 : 0 \
+			: 0)
+
+/**
+ * safe_conversion - perform a type conversion (cast) of an source value into
+ * a new variable, checking that the destination is large enough to hold the
+ * source value.
+ * @ptr: Destination pointer address
+ * @value: Source value
+ *
+ * Returns:
+ * If the value would overflow the destination, it returns false.
+ */
+#define safe_conversion(ptr, value) ({ \
+	typeof(value) __v = (value); \
+	typeof(ptr) __ptr = (ptr); \
+	overflows_type(__v, *__ptr) ? 0 : ((*__ptr = (typeof(*__ptr))__v), 1); \
+})
+
 /*
  * Avoids triggering -Wtype-limits compilation warning,
  * while using unsigned data types to check a < 0.
-- 
2.34.1