From: Eliav Farber <farbere@amazon•com>
To: <gregkh@linuxfoundation•org>, <stable@vger•kernel.org>,
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Cc: Arnd Bergmann <arnd@kernel•org>,
Christoph Hellwig <hch@infradead•org>,
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Jens Axboe <axboe@kernel•dk>,
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Pedro Falcato <pedro.falcato@gmail•com>
Subject: [PATCH v2 22/27 5.10.y] minmax.h: update some comments
Date: Fri, 17 Oct 2025 09:05:14 +0000 [thread overview]
Message-ID: <20251017090519.46992-23-farbere@amazon.com> (raw)
In-Reply-To: <20251017090519.46992-1-farbere@amazon.com>
From: David Laight <David.Laight@ACULAB•COM>
[ Upstream commit 10666e99204818ef45c702469488353b5bb09ec7 ]
- Change three to several.
- Remove the comment about retaining constant expressions, no longer true.
- Realign to nearer 80 columns and break on major punctiation.
- Add a leading comment to the block before __signed_type() and __is_nonneg()
Otherwise the block explaining the cast is a bit 'floating'.
Reword the rest of that comment to improve readability.
Link: https://lkml.kernel.org/r/85b050c81c1d4076aeb91a6cded45fee@AcuMS.aculab.com
Signed-off-by: David Laight <david.laight@aculab•com>
Cc: Andy Shevchenko <andriy.shevchenko@linux•intel.com>
Cc: Arnd Bergmann <arnd@kernel•org>
Cc: Christoph Hellwig <hch@infradead•org>
Cc: Dan Carpenter <dan.carpenter@linaro•org>
Cc: Jason A. Donenfeld <Jason@zx2c4•com>
Cc: Jens Axboe <axboe@kernel•dk>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle•com>
Cc: Mateusz Guzik <mjguzik@gmail•com>
Cc: Matthew Wilcox <willy@infradead•org>
Cc: Pedro Falcato <pedro.falcato@gmail•com>
Signed-off-by: Andrew Morton <akpm@linux-foundation•org>
Signed-off-by: Eliav Farber <farbere@amazon•com>
---
include/linux/minmax.h | 53 +++++++++++++++++++-----------------------
1 file changed, 24 insertions(+), 29 deletions(-)
diff --git a/include/linux/minmax.h b/include/linux/minmax.h
index 51b0d988e322..24e4b372649a 100644
--- a/include/linux/minmax.h
+++ b/include/linux/minmax.h
@@ -8,13 +8,10 @@
#include <linux/types.h>
/*
- * min()/max()/clamp() macros must accomplish three things:
+ * min()/max()/clamp() macros must accomplish several things:
*
* - Avoid multiple evaluations of the arguments (so side-effects like
* "x++" happen only once) when non-constant.
- * - 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
@@ -31,25 +28,23 @@
* bit #0 set if ok for unsigned comparisons
* bit #1 set if ok for signed comparisons
*
- * In particular, statically non-negative signed integer
- * expressions are ok for both.
+ * In particular, statically non-negative signed integer expressions
+ * are ok for both.
*
- * NOTE! Unsigned types smaller than 'int' are implicitly
- * converted to 'int' in expressions, and are accepted for
- * signed conversions for now. This is debatable.
+ * NOTE! Unsigned types smaller than 'int' are implicitly converted to 'int'
+ * in expressions, and are accepted for signed conversions for now.
+ * This is debatable.
*
- * Note that 'x' is the original expression, and 'ux' is
- * the unique variable that contains the value.
+ * Note that 'x' is the original expression, and 'ux' is the unique variable
+ * that contains the value.
*
- * We use 'ux' for pure type checking, and 'x' for when
- * we need to look at the value (but without evaluating
- * it for side effects! Careful to only ever evaluate it
- * with sizeof() or __builtin_constant_p() etc).
+ * We use 'ux' for pure type checking, and 'x' for when we need to look at the
+ * value (but without evaluating it for side effects!
+ * Careful to only ever evaluate it with sizeof() or __builtin_constant_p() etc).
*
- * Pointers end up being checked by the normal C type
- * rules at the actual comparison, and these expressions
- * only need to be careful to not cause warnings for
- * pointer use.
+ * Pointers end up being checked by the normal C type rules at the actual
+ * comparison, and these expressions only need to be careful to not cause
+ * warnings for pointer use.
*/
#define __signed_type_use(x, ux) (2 + __is_nonneg(x, ux))
#define __unsigned_type_use(x, ux) (1 + 2 * (sizeof(ux) < 4))
@@ -57,19 +52,19 @@
__signed_type_use(x, ux) : __unsigned_type_use(x, ux))
/*
- * To avoid warnings about casting pointers to integers
- * of different sizes, we need that special sign type.
+ * Check whether a signed value is always non-negative.
*
- * On 64-bit we can just always use 'long', since any
- * integer or pointer type can just be cast to that.
+ * A cast is needed to avoid any warnings from values that aren't signed
+ * integer types (in which case the result doesn't matter).
*
- * This does not work for 128-bit signed integers since
- * the cast would truncate them, but we do not use s128
- * types in the kernel (we do use 'u128', but they will
- * be handled by the !is_signed_type() case).
+ * On 64-bit any integer or pointer type can safely be cast to 'long'.
+ * But on 32-bit we need to avoid warnings about casting pointers to integers
+ * of different sizes without truncating 64-bit values so 'long' or 'long long'
+ * must be used depending on the size of the value.
*
- * NOTE! The cast is there only to avoid any warnings
- * from when values that aren't signed integer types.
+ * This does not work for 128-bit signed integers since the cast would truncate
+ * them, but we do not use s128 types in the kernel (we do use 'u128',
+ * but they are handled by the !is_signed_type() case).
*/
#ifdef CONFIG_64BIT
#define __signed_type(ux) long
--
2.47.3
next prev parent reply other threads:[~2025-10-17 9:12 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-17 9:04 [PATCH v2 00/27 5.10.y] Backport minmax.h updates from v6.17-rc7 Eliav Farber
2025-10-17 9:04 ` [PATCH v2 01/27 5.10.y] overflow, tracing: Define the is_signed_type() macro once Eliav Farber
2025-10-17 11:59 ` Greg KH
2025-10-17 12:16 ` Farber, Eliav
2025-10-17 13:21 ` Greg KH
2025-10-17 9:04 ` [PATCH v2 02/27 5.10.y] btrfs: remove duplicated in_range() macro Eliav Farber
2025-10-17 9:04 ` [PATCH v2 03/27 5.10.y] minmax: sanity check constant bounds when clamping Eliav Farber
2025-10-17 9:04 ` [PATCH v2 04/27 5.10.y] minmax: clamp more efficiently by avoiding extra comparison Eliav Farber
2025-10-17 9:04 ` [PATCH v2 05/27 5.10.y] minmax: add in_range() macro Eliav Farber
2025-10-17 9:04 ` [PATCH v2 06/27 5.10.y] minmax: Introduce {min,max}_array() Eliav Farber
2025-10-17 9:04 ` [PATCH v2 07/27 5.10.y] minmax: deduplicate __unconst_integer_typeof() Eliav Farber
2025-10-17 9:05 ` [PATCH v2 08/27 5.10.y] minmax: fix header inclusions Eliav Farber
2025-10-17 9:05 ` [PATCH v2 09/27 5.10.y] minmax: allow min()/max()/clamp() if the arguments have the same signedness Eliav Farber
2025-10-17 9:05 ` [PATCH v2 10/27 5.10.y] minmax: fix indentation of __cmp_once() and __clamp_once() Eliav Farber
2025-10-17 9:05 ` [PATCH v2 11/27 5.10.y] minmax: allow comparisons of 'int' against 'unsigned char/short' Eliav Farber
2025-10-17 9:05 ` [PATCH v2 12/27 5.10.y] minmax: relax check to allow comparison between unsigned arguments and signed constants Eliav Farber
2025-10-17 9:05 ` [PATCH v2 13/27 5.10.y] minmax: avoid overly complicated constant expressions in VM code Eliav Farber
2025-10-17 9:05 ` [PATCH v2 14/27 5.10.y] minmax: add a few more MIN_T/MAX_T users Eliav Farber
2025-10-17 9:05 ` [PATCH v2 15/27 5.10.y] minmax: simplify and clarify min_t()/max_t() implementation Eliav Farber
2025-10-17 9:05 ` [PATCH v2 16/27 5.10.y] minmax: make generic MIN() and MAX() macros available everywhere Eliav Farber
2025-10-17 9:05 ` [PATCH v2 17/27 5.10.y] minmax: don't use max() in situations that want a C constant expression Eliav Farber
2025-10-17 9:05 ` [PATCH v2 18/27 5.10.y] minmax: simplify min()/max()/clamp() implementation Eliav Farber
2025-10-17 9:05 ` [PATCH v2 19/27 5.10.y] minmax: improve macro expansion and type checking Eliav Farber
2025-10-17 9:05 ` [PATCH v2 20/27 5.10.y] minmax: fix up min3() and max3() too Eliav Farber
2025-10-17 9:05 ` [PATCH v2 21/27 5.10.y] minmax.h: add whitespace around operators and after commas Eliav Farber
2025-10-17 9:05 ` Eliav Farber [this message]
2025-10-17 9:05 ` [PATCH v2 23/27 5.10.y] minmax.h: reduce the #define expansion of min(), max() and clamp() Eliav Farber
2025-10-17 9:05 ` [PATCH v2 24/27 5.10.y] minmax.h: use BUILD_BUG_ON_MSG() for the lo < hi test in clamp() Eliav Farber
2025-10-17 9:05 ` [PATCH v2 25/27 5.10.y] minmax.h: move all the clamp() definitions after the min/max() ones Eliav Farber
2025-10-17 9:05 ` [PATCH v2 26/27 5.10.y] minmax.h: simplify the variants of clamp() Eliav Farber
2025-10-17 9:05 ` [PATCH v2 27/27 5.10.y] minmax.h: remove some #defines that are only expanded once Eliav Farber
2025-10-17 15:03 ` [PATCH v2 00/27 5.10.y] Backport minmax.h updates from v6.17-rc7 Greg KH
2025-10-17 16:09 ` Nathan Chancellor
2025-10-19 12:38 ` Greg KH
2025-10-18 20:07 ` Farber, Eliav
2025-10-19 12:37 ` Greg KH
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