[PATCH v3 5/5] minmax: Relax check to allow comparison between int and small unsigned constants.

David Laight
2023-08-04T10:58:48Z

Convert constants between 0 and INT_MAX to 'int' prior to comparisons
so that min(signed_var, 20u) and, more commonly, min(signed_var, sizeof())
are both valid.

Signed-off-by: David Laight <david.laight@aculab.com>
---
v3: Fix compiler warnings for 'x >= 0' with unsigned/pointer types.
v2: Add cast to fix min/max with pointer types.
include/linux/minmax.h | 34 ++++++++++++++++++++++------------
1 file changed, 22 insertions(+), 12 deletions(-)

diff --git a/include/linux/minmax.h b/include/linux/minmax.h
index f56611ab486a..8d292aa55f5f 100644
--- a/include/linux/minmax.h
+++ b/include/linux/minmax.h
@@ -8,11 +8,13 @@
/*
* min()/max()/clamp() macros must accomplish three things:
*
- * - avoid multiple evaluations of the arguments (so side-effects like
+ * - Avoid multiple evaluations of the arguments (so side-effects like
* "x++" happen only once) when non-constant.
- * - perform signed v unsigned type-checking (to generate compile
+ * - Perform signed v unsigned type-checking (to generate compile
* errors instead of nasty runtime surprises).
- * - retain result as a constant expressions when called with only
+ * Constants from 0 to INT_MAX are cast to (int) so can be used
+ * in comparisons with signed types.
+ * - Retain result as a constant expressions when called with only
* constant expressions (to avoid tripping VLA warnings in stack
* allocation usage).
*/
@@ -24,9 +26,17 @@
__builtin_choose_expr(__is_constexpr(is_signed_type(typeof(x))), \
is_signed_type(typeof(x)), 0)

-#define __types_ok(x, y) \
- (__is_signed(x) == __is_signed(y) || \
- __is_signed((x) + 0) == __is_signed((y) + 0))
+#define __is_noneg_int(x) \
+ (__builtin_choose_expr(!__is_constexpr(x), false, \
+ __builtin_choose_expr(__is_signed(x), x, 0) >= 0 && \
+ (x) <= (typeof((x) + 0))(long)__INT_MAX__))
+
+#define __int_const(x) __builtin_choose_expr(__is_noneg_int(x), (int)(long)(x), (x))
+
+#define __types_ok(x, y) \
+ (__is_signed(x) == __is_signed(y) || \
+ __is_signed((x) + 0) == __is_signed((y) + 0) || \
+ __is_noneg_int(x) || __is_noneg_int(y))

#define __cmp_op_min <
#define __cmp_op_max >
@@ -34,24 +44,24 @@
#define __cmp(op, x, y) ((x) __cmp_op_##op (y) ? (x) : (y))

#define __cmp_once(op, x, y, unique_x, unique_y) ({ \
- typeof(x) unique_x = (x); \
- typeof(y) unique_y = (y); \
+ typeof(__int_const(x)) unique_x = (x); \
+ typeof(__int_const(y)) unique_y = (y); \
static_assert(__types_ok(x, y), \
#op "(" #x ", " #y ") signedness error, fix types or consider " #op "_unsigned() before " #op "_t()"); \
__cmp(op, unique_x, unique_y); })

#define __careful_cmp(op, x, y) \
__builtin_choose_expr(__is_constexpr((x) - (y)), \
- __cmp(op, x, y), \
+ __cmp(op, __int_const(x), __int_const(y)), \
__cmp_once(op, x, y, __UNIQUE_ID(__x), __UNIQUE_ID(__y)))

#define __clamp(val, lo, hi) \
((val) >= (hi) ? (hi) : ((val) <= (lo) ? (lo) : (val)))

#define __clamp_once(val, lo, hi, unique_val, unique_lo, unique_hi) ({ \
- typeof(val) unique_val = (val); \
- typeof(lo) unique_lo = (lo); \
- typeof(hi) unique_hi = (hi); \
+ typeof(__int_const(val)) unique_val = (val); \
+ typeof(__int_const(lo)) unique_lo = (lo); \
+ typeof(__int_const(hi)) unique_hi = (hi); \
static_assert(__builtin_choose_expr(__is_constexpr((lo) > (hi)), \
(lo) <= (hi), true), \
"clamp() low limit " #lo " greater than high limit " #hi); \
--
2.17.1