[PATCH 1/3] include: sync min/max definitions with Linux
Ahmad Fatoum
ahmad at a3f.at
Tue May 30 23:28:51 PDT 2023
By syncing to Linux, min/max and friends now return constant expressions
if possible, which makes them suitable for use as non-VLA array length.
Signed-off-by: Ahmad Fatoum <ahmad at a3f.at>
---
include/linux/const.h | 9 +++
include/linux/kernel.h | 123 +-----------------------------
include/linux/minmax.h | 169 +++++++++++++++++++++++++++++++++++++++++
3 files changed, 179 insertions(+), 122 deletions(-)
create mode 100644 include/linux/minmax.h
diff --git a/include/linux/const.h b/include/linux/const.h
index 07f886d27155..0acddd3a0ed6 100644
--- a/include/linux/const.h
+++ b/include/linux/const.h
@@ -26,4 +26,13 @@
#define _BITUL(x) (_AC(1,UL) << (x))
#define _BITULL(x) (_AC(1,ULL) << (x))
+
+/*
+ * This returns a constant expression while determining if an argument is
+ * a constant expression, most importantly without evaluating the argument.
+ * Glory to Martin Uecker <Martin.Uecker at med.uni-goettingen.de>
+ */
+#define __is_constexpr(x) \
+ (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
+
#endif /* !(_LINUX_CONST_H) */
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 0eb7bd21fe93..bf820de22ca7 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -8,6 +8,7 @@
#include <linux/limits.h>
#include <linux/math64.h>
#include <linux/container_of.h>
+#include <linux/minmax.h>
#define ALIGN(x, a) __ALIGN_MASK(x, (typeof(x))(a) - 1)
#define ALIGN_DOWN(x, a) ALIGN((x) - ((a) - 1), (a))
@@ -88,121 +89,6 @@ extern long simple_strtol(const char *,char **,unsigned int);
extern unsigned long long simple_strtoull(const char *,char **,unsigned int);
extern long long simple_strtoll(const char *,char **,unsigned int);
-/*
- * min()/max()/clamp() macros that also do
- * strict type-checking.. See the
- * "unnecessary" pointer comparison.
- */
-#define min(x, y) ({ \
- typeof(x) _min1 = (x); \
- typeof(y) _min2 = (y); \
- (void) (&_min1 == &_min2); \
- _min1 < _min2 ? _min1 : _min2; })
-
-#define max(x, y) ({ \
- typeof(x) _max1 = (x); \
- typeof(y) _max2 = (y); \
- (void) (&_max1 == &_max2); \
- _max1 > _max2 ? _max1 : _max2; })
-
-#define min3(x, y, z) ({ \
- typeof(x) _min1 = (x); \
- typeof(y) _min2 = (y); \
- typeof(z) _min3 = (z); \
- (void) (&_min1 == &_min2); \
- (void) (&_min1 == &_min3); \
- _min1 < _min2 ? (_min1 < _min3 ? _min1 : _min3) : \
- (_min2 < _min3 ? _min2 : _min3); })
-
-#define max3(x, y, z) ({ \
- typeof(x) _max1 = (x); \
- typeof(y) _max2 = (y); \
- typeof(z) _max3 = (z); \
- (void) (&_max1 == &_max2); \
- (void) (&_max1 == &_max3); \
- _max1 > _max2 ? (_max1 > _max3 ? _max1 : _max3) : \
- (_max2 > _max3 ? _max2 : _max3); })
-
-/**
- * min_not_zero - return the minimum that is _not_ zero, unless both are zero
- * @x: value1
- * @y: value2
- */
-#define min_not_zero(x, y) ({ \
- typeof(x) __x = (x); \
- typeof(y) __y = (y); \
- __x == 0 ? __y : ((__y == 0) ? __x : min(__x, __y)); })
-
-/**
- * clamp - return a value clamped to a given range with strict typechecking
- * @val: current value
- * @min: minimum allowable value
- * @max: maximum allowable value
- *
- * This macro does strict typechecking of min/max to make sure they are of the
- * same type as val. See the unnecessary pointer comparisons.
- */
-#define clamp(val, min, max) ({ \
- typeof(val) __val = (val); \
- typeof(min) __min = (min); \
- typeof(max) __max = (max); \
- (void) (&__val == &__min); \
- (void) (&__val == &__max); \
- __val = __val < __min ? __min: __val; \
- __val > __max ? __max: __val; })
-
-/*
- * ..and if you can't take the strict
- * types, you can specify one yourself.
- *
- * Or not use min/max/clamp at all, of course.
- */
-#define min_t(type, x, y) ({ \
- type __min1 = (x); \
- type __min2 = (y); \
- __min1 < __min2 ? __min1: __min2; })
-
-#define max_t(type, x, y) ({ \
- type __max1 = (x); \
- type __max2 = (y); \
- __max1 > __max2 ? __max1: __max2; })
-
-/**
- * clamp_t - return a value clamped to a given range using a given type
- * @type: the type of variable to use
- * @val: current value
- * @min: minimum allowable value
- * @max: maximum allowable value
- *
- * This macro does no typechecking and uses temporary variables of type
- * 'type' to make all the comparisons.
- */
-#define clamp_t(type, val, min, max) ({ \
- type __val = (val); \
- type __min = (min); \
- type __max = (max); \
- __val = __val < __min ? __min: __val; \
- __val > __max ? __max: __val; })
-
-/**
- * clamp_val - return a value clamped to a given range using val's type
- * @val: current value
- * @min: minimum allowable value
- * @max: maximum allowable value
- *
- * This macro does no typechecking and uses temporary variables of whatever
- * type the input argument 'val' is. This is useful when val is an unsigned
- * type and min and max are literals that will otherwise be assigned a signed
- * integer type.
- */
-#define clamp_val(val, min, max) ({ \
- typeof(val) __val = (val); \
- typeof(val) __min = (min); \
- typeof(val) __max = (max); \
- __val = __val < __min ? __min: __val; \
- __val > __max ? __max: __val; })
-
-
/* The `const' in roundup() prevents gcc-3.3 from calling __divdi3 */
#define roundup(x, y) ( \
{ \
@@ -257,13 +143,6 @@ extern int hex_to_bin(char ch);
extern int __must_check hex2bin(u8 *dst, const char *src, size_t count);
extern char *bin2hex(char *dst, const void *src, size_t count);
-/*
- * swap - swap value of @a and @b
- */
-#define swap(a, b) \
- do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)
-
-
/* Internal, do not use. */
int __must_check _kstrtoul(const char *s, unsigned int base, unsigned long *res);
int __must_check _kstrtol(const char *s, unsigned int base, long *res);
diff --git a/include/linux/minmax.h b/include/linux/minmax.h
new file mode 100644
index 000000000000..396df1121bff
--- /dev/null
+++ b/include/linux/minmax.h
@@ -0,0 +1,169 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_MINMAX_H
+#define _LINUX_MINMAX_H
+
+#include <linux/const.h>
+
+/*
+ * min()/max()/clamp() macros must accomplish three things:
+ *
+ * - avoid multiple evaluations of the arguments (so side-effects like
+ * "x++" happen only once) when non-constant.
+ * - perform strict type-checking (to generate warnings instead of
+ * nasty runtime surprises). See the "unnecessary" pointer comparison
+ * in __typecheck().
+ * - retain result as a constant expressions when called with only
+ * constant expressions (to avoid tripping VLA warnings in stack
+ * allocation usage).
+ */
+#define __typecheck(x, y) \
+ (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
+
+#define __no_side_effects(x, y) \
+ (__is_constexpr(x) && __is_constexpr(y))
+
+#define __safe_cmp(x, y) \
+ (__typecheck(x, y) && __no_side_effects(x, y))
+
+#define __cmp(x, y, op) ((x) op (y) ? (x) : (y))
+
+#define __cmp_once(x, y, unique_x, unique_y, op) ({ \
+ typeof(x) unique_x = (x); \
+ typeof(y) unique_y = (y); \
+ __cmp(unique_x, unique_y, op); })
+
+#define __careful_cmp(x, y, op) \
+ __builtin_choose_expr(__safe_cmp(x, y), \
+ __cmp(x, y, op), \
+ __cmp_once(x, y, __UNIQUE_ID(__x), __UNIQUE_ID(__y), op))
+
+#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); \
+ __clamp(unique_val, unique_lo, unique_hi); })
+
+#define __clamp_input_check(lo, hi) \
+ (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
+ __is_constexpr((lo) > (hi)), (lo) > (hi), false)))
+
+#define __careful_clamp(val, lo, hi) ({ \
+ __clamp_input_check(lo, hi) + \
+ __builtin_choose_expr(__typecheck(val, lo) && __typecheck(val, hi) && \
+ __typecheck(hi, lo) && __is_constexpr(val) && \
+ __is_constexpr(lo) && __is_constexpr(hi), \
+ __clamp(val, lo, hi), \
+ __clamp_once(val, lo, hi, __UNIQUE_ID(__val), \
+ __UNIQUE_ID(__lo), __UNIQUE_ID(__hi))); })
+
+/**
+ * min - return minimum of two values of the same or compatible types
+ * @x: first value
+ * @y: second value
+ */
+#define min(x, y) __careful_cmp(x, y, <)
+
+/**
+ * max - return maximum of two values of the same or compatible types
+ * @x: first value
+ * @y: second value
+ */
+#define max(x, y) __careful_cmp(x, y, >)
+
+/**
+ * min3 - return minimum of three values
+ * @x: first value
+ * @y: second value
+ * @z: third value
+ */
+#define min3(x, y, z) min((typeof(x))min(x, y), z)
+
+/**
+ * max3 - return maximum of three values
+ * @x: first value
+ * @y: second value
+ * @z: third value
+ */
+#define max3(x, y, z) max((typeof(x))max(x, y), z)
+
+/**
+ * min_not_zero - return the minimum that is _not_ zero, unless both are zero
+ * @x: value1
+ * @y: value2
+ */
+#define min_not_zero(x, y) ({ \
+ typeof(x) __x = (x); \
+ typeof(y) __y = (y); \
+ __x == 0 ? __y : ((__y == 0) ? __x : min(__x, __y)); })
+
+/**
+ * clamp - return a value clamped to a given range with strict typechecking
+ * @val: current value
+ * @lo: lowest allowable value
+ * @hi: highest allowable value
+ *
+ * This macro does strict typechecking of @lo/@hi to make sure they are of the
+ * same type as @val. See the unnecessary pointer comparisons.
+ */
+#define clamp(val, lo, hi) __careful_clamp(val, lo, hi)
+
+/*
+ * ..and if you can't take the strict
+ * types, you can specify one yourself.
+ *
+ * Or not use min/max/clamp at all, of course.
+ */
+
+/**
+ * min_t - return minimum of two values, using the specified type
+ * @type: data type to use
+ * @x: first value
+ * @y: second value
+ */
+#define min_t(type, x, y) __careful_cmp((type)(x), (type)(y), <)
+
+/**
+ * max_t - return maximum of two values, using the specified type
+ * @type: data type to use
+ * @x: first value
+ * @y: second value
+ */
+#define max_t(type, x, y) __careful_cmp((type)(x), (type)(y), >)
+
+/**
+ * clamp_t - return a value clamped to a given range using a given type
+ * @type: the type of variable to use
+ * @val: current value
+ * @lo: minimum allowable value
+ * @hi: maximum allowable value
+ *
+ * This macro does no typechecking and uses temporary variables of type
+ * @type to make all the comparisons.
+ */
+#define clamp_t(type, val, lo, hi) __careful_clamp((type)(val), (type)(lo), (type)(hi))
+
+/**
+ * clamp_val - return a value clamped to a given range using val's type
+ * @val: current value
+ * @lo: minimum allowable value
+ * @hi: maximum allowable value
+ *
+ * This macro does no typechecking and uses temporary variables of whatever
+ * type the input argument @val is. This is useful when @val is an unsigned
+ * type and @lo and @hi are literals that will otherwise be assigned a signed
+ * integer type.
+ */
+#define clamp_val(val, lo, hi) clamp_t(typeof(val), val, lo, hi)
+
+/**
+ * swap - swap values of @a and @b
+ * @a: first value
+ * @b: second value
+ */
+#define swap(a, b) \
+ do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)
+
+#endif /* _LINUX_MINMAX_H */
--
2.38.5
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