[PATCH v2 15/27 5.10.y] minmax: simplify and clarify min_t()/max_t() implementation

Eliav Farber
2025-10-17T09:10:25Z

From: Linus Torvalds <torvalds@linux-foundation.org>

[ Upstream commit 017fa3e89187848fd056af757769c9e66ac3e93d ]

This simplifies the min_t() and max_t() macros by no longer making them
work in the context of a C constant expression.

That means that you can no longer use them for static initializers or
for array sizes in type definitions, but there were only a couple of
such uses, and all of them were converted (famous last words) to use
MIN_T/MAX_T instead.

Cc: David Laight <David.Laight@aculab.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Eliav Farber <farbere@amazon.com>
---
include/linux/minmax.h | 19 +++++++++++--------
1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/include/linux/minmax.h b/include/linux/minmax.h
index a7ef65f78933..9c2848abc804 100644
--- a/include/linux/minmax.h
+++ b/include/linux/minmax.h
@@ -45,17 +45,20 @@

#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); \
+#define __cmp_once_unique(op, type, x, y, ux, uy) \
+ ({ type ux = (x); type uy = (y); __cmp(op, ux, uy); })
+
+#define __cmp_once(op, type, x, y) \
+ __cmp_once_unique(op, type, x, y, __UNIQUE_ID(x_), __UNIQUE_ID(y_))
+
+#define __careful_cmp_once(op, x, y) ({ \
static_assert(__types_ok(x, y), \
#op "(" #x ", " #y ") signedness error, fix types or consider u" #op "() before " #op "_t()"); \
- __cmp(op, unique_x, unique_y); })
+ __cmp_once(op, __auto_type, x, y); })

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

#define __clamp(val, lo, hi) \
((val) >= (hi) ? (hi) : ((val) <= (lo) ? (lo) : (val)))
@@ -158,7 +161,7 @@
* @x: first value
* @y: second value
*/
-#define min_t(type, x, y) __careful_cmp(min, (type)(x), (type)(y))
+#define min_t(type, x, y) __cmp_once(min, type, x, y)

/**
* max_t - return maximum of two values, using the specified type
@@ -166,7 +169,7 @@
* @x: first value
* @y: second value
*/
-#define max_t(type, x, y) __careful_cmp(max, (type)(x), (type)(y))
+#define max_t(type, x, y) __cmp_once(max, type, x, y)

/*
* Do not check the array parameter using __must_be_array().
--
2.47.3