The patch titled
Subject: minmax.h: update some comments
has been added to the -mm mm-nonmm-unstable branch. Its filename is
minmaxh-update-some-comments.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/minmaxh-update-some-comments.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.h: update some comments
Date: Mon, 18 Nov 2024 19:12:07 +0000
- 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@xxxxxxxxxxxxxxxx
Signed-off-by: David Laight <david.laight@xxxxxxxxxx>
Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Cc: Jason A. Donenfeld <Jason@xxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Cc: Mateusz Guzik <mjguzik@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Pedro Falcato <pedro.falcato@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/minmax.h | 61 +++++++++++++++++----------------------
1 file changed, 28 insertions(+), 33 deletions(-)
--- a/include/linux/minmax.h~minmaxh-update-some-comments
+++ a/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 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).
- *
- * 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.
+ * 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.
+ *
+ * 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.
*/
#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).
- *
- * NOTE! The cast is there only to avoid any warnings
- * from when values that aren't signed integer types.
+ * 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.
+ *
+ * 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
_
Patches currently in -mm which might be from David.Laight@xxxxxxxxxx are
minmaxh-add-whitespace-around-operators-and-after-commas.patch
minmaxh-update-some-comments.patch
minmaxh-reduce-the-define-expansion-of-min-max-and-clamp.patch
minmaxh-use-build_bug_on_msg-for-the-lo-hi-test-in-clamp.patch
minmaxh-move-all-the-clamp-definitions-after-the-min-max-ones.patch
minmaxh-simplify-the-variants-of-clamp.patch
minmaxh-remove-some-defines-that-are-only-expanded-once.patch
