The patch titled
Subject: minmax: relax check to allow comparison between unsigned arguments and signed constants
has been added to the -mm mm-nonmm-unstable branch. Its filename is
minmax-relax-check-to-allow-comparison-between-unsigned-arguments-and-signed-constants.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/minmax-relax-check-to-allow-comparison-between-unsigned-arguments-and-signed-constants.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: David Laight <David.Laight@xxxxxxxxxx>
Subject: minmax: relax check to allow comparison between unsigned arguments and signed constants
Date: Mon, 18 Sep 2023 08:19:25 +0000
Allow (for example) min(unsigned_var, 20).
The opposite min(signed_var, 20u) is still errored.
Since a comparison between signed and unsigned never makes the unsigned
value negative it is only necessary to adjust the __types_ok() test.
Link: https://lkml.kernel.org/r/633b64e2f39e46bb8234809c5595b8c7@xxxxxxxxxxxxxxxx
Signed-off-by: David Laight <david.laight@xxxxxxxxxx>
Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Jason A. Donenfeld <Jason@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/minmax.h | 24 +++++++++++++++++-------
1 file changed, 17 insertions(+), 7 deletions(-)
--- a/include/linux/minmax.h~minmax-relax-check-to-allow-comparison-between-unsigned-arguments-and-signed-constants
+++ a/include/linux/minmax.h
@@ -10,13 +10,18 @@
/*
* 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
- * errors instead of nasty runtime surprises).
- * - retain result as a constant expressions when called with only
+ * - Retain result as a constant expressions when called with only
* constant expressions (to avoid tripping VLA warnings in stack
* allocation usage).
+ * - Perform signed v unsigned type-checking (to generate compile
+ * errors instead of nasty runtime surprises).
+ * - Unsigned char/short are always promoted to signed int and can be
+ * compared against signed or unsigned arguments.
+ * - Unsigned arguments can be compared against non-negative signed constants.
+ * - Comparison of a signed argument against an unsigned constant fails
+ * even if the constant is below __INT_MAX__ and could be cast to int.
*/
#define __typecheck(x, y) \
(!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
@@ -26,9 +31,14 @@
__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))
+/* True for a non-negative signed int constant */
+#define __is_noneg_int(x) \
+ (__builtin_choose_expr(__is_constexpr(x) && __is_signed(x), x, -1) >= 0)
+
+#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 >
_
Patches currently in -mm which might be from David.Laight@xxxxxxxxxx are
minmax-add-umina-b-and-umaxa-b.patch
minmax-allow-min-max-clamp-if-the-arguments-have-the-same-signedness.patch
minmax-fix-indentation-of-__cmp_once-and-__clamp_once.patch
minmax-allow-comparisons-of-int-against-unsigned-char-short.patch
minmax-relax-check-to-allow-comparison-between-unsigned-arguments-and-signed-constants.patch
