git: c44d2663a790 - main - rb tree: remove strict aliasing violations
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Date: Wed, 15 Oct 2025 07:25:27 UTC
The branch main has been updated by rlibby:
URL: https://cgit.FreeBSD.org/src/commit/?id=c44d2663a790b31bc1cd08958b45a661487c0287
commit c44d2663a790b31bc1cd08958b45a661487c0287
Author: Ryan Libby <rlibby@FreeBSD.org>
AuthorDate: 2025-10-15 04:05:19 +0000
Commit: Ryan Libby <rlibby@FreeBSD.org>
CommitDate: 2025-10-15 06:44:47 +0000
rb tree: remove strict aliasing violations
Rework internal RB macros to avoid assignments via type punned pointers.
RB uses low order pointer bits to encode information (whether children
are red), and was manipulating those values via (*(__uintptr_t *)&elm),
which leads to strict aliasing warnings.
In the kernel we use -fno-strict-aliasing, but this isn't necessarily
the case in user space. This quiets thousands of -Wstrict-aliasing
warnings in the user space build.
Reported by: GCC -Wstrict-aliasing
Reviewed by: dougm
Discussed with: kib
Differential Revision: https://reviews.freebsd.org/D52939
---
sys/sys/tree.h | 57 ++++++++++++++++++++++++++++++++++-----------------------
1 file changed, 34 insertions(+), 23 deletions(-)
diff --git a/sys/sys/tree.h b/sys/sys/tree.h
index c11bccfb387c..194ad505b038 100644
--- a/sys/sys/tree.h
+++ b/sys/sys/tree.h
@@ -334,10 +334,13 @@ struct { \
#define _RB_L ((__uintptr_t)1)
#define _RB_R ((__uintptr_t)2)
#define _RB_LR ((__uintptr_t)3)
-#define _RB_BITS(elm) (*(__uintptr_t *)&elm)
+#define _RB_BITS(elm) ((__uintptr_t)elm)
#define _RB_BITSUP(elm, field) _RB_BITS(_RB_UP(elm, field))
-#define _RB_PTR(elm) (__typeof(elm)) \
- ((__uintptr_t)elm & ~_RB_LR)
+#define _RB_PTR_OP(elm, op, dir) ((__typeof(elm)) \
+ ((__uintptr_t)(elm) op (dir)))
+#define _RB_PTR(elm) _RB_PTR_OP((elm), &, ~_RB_LR)
+#define _RB_MOD_OR(elm, dir) ((elm) = _RB_PTR_OP((elm), |, (dir)))
+#define _RB_MOD_XOR(elm, dir) ((elm) = _RB_PTR_OP((elm), ^, (dir)))
#define RB_PARENT(elm, field) _RB_PTR(_RB_UP(elm, field))
#define RB_LEFT(elm, field) _RB_LINK(elm, _RB_L, field)
@@ -346,8 +349,8 @@ struct { \
#define RB_EMPTY(head) (RB_ROOT(head) == NULL)
#define RB_SET_PARENT(dst, src, field) do { \
- _RB_BITSUP(dst, field) = (__uintptr_t)src | \
- (_RB_BITSUP(dst, field) & _RB_LR); \
+ _RB_UP(dst, field) = (__typeof(src))((__uintptr_t)src | \
+ (_RB_BITSUP(dst, field) & _RB_LR)); \
} while (/*CONSTCOND*/ 0)
#define RB_SET(elm, parent, field) do { \
@@ -546,12 +549,12 @@ name##_RB_INSERT_COLOR(struct name *head, \
elmdir = RB_RIGHT(parent, field) == elm ? _RB_R : _RB_L; \
if (_RB_BITS(gpar) & elmdir) { \
/* shorten the parent-elm edge to rebalance */ \
- _RB_BITSUP(parent, field) ^= elmdir; \
+ _RB_MOD_XOR(_RB_UP(parent, field), elmdir); \
return (NULL); \
} \
sibdir = elmdir ^ _RB_LR; \
/* the other edge must change length */ \
- _RB_BITSUP(parent, field) ^= sibdir; \
+ _RB_MOD_XOR(_RB_UP(parent, field), sibdir); \
if ((_RB_BITS(gpar) & _RB_LR) == 0) { \
/* both edges now short, retry from parent */ \
child = elm; \
@@ -583,11 +586,14 @@ name##_RB_INSERT_COLOR(struct name *head, \
RB_ROTATE(elm, child, elmdir, field); \
child_up = _RB_UP(child, field); \
if (_RB_BITS(child_up) & sibdir) \
- _RB_BITSUP(parent, field) ^= elmdir; \
+ _RB_MOD_XOR(_RB_UP(parent, field), \
+ elmdir); \
if (_RB_BITS(child_up) & elmdir) \
- _RB_BITSUP(elm, field) ^= _RB_LR; \
+ _RB_MOD_XOR(_RB_UP(elm, field), \
+ _RB_LR); \
else \
- _RB_BITSUP(elm, field) ^= elmdir; \
+ _RB_MOD_XOR(_RB_UP(elm, field), \
+ elmdir); \
/* if child is a leaf, don't augment elm, \
* since it is restored to be a leaf again. */ \
if ((_RB_BITS(child_up) & _RB_LR) == 0) \
@@ -656,7 +662,7 @@ name##_RB_REMOVE_COLOR(struct name *head, \
/* the rank of the tree rooted at elm shrank */ \
gpar = _RB_UP(parent, field); \
elmdir = RB_RIGHT(parent, field) == elm ? _RB_R : _RB_L; \
- _RB_BITS(gpar) ^= elmdir; \
+ _RB_MOD_XOR(gpar, elmdir); \
if (_RB_BITS(gpar) & elmdir) { \
/* lengthen the parent-elm edge to rebalance */ \
_RB_UP(parent, field) = gpar; \
@@ -664,7 +670,7 @@ name##_RB_REMOVE_COLOR(struct name *head, \
} \
if (_RB_BITS(gpar) & _RB_LR) { \
/* shorten other edge, retry from parent */ \
- _RB_BITS(gpar) ^= _RB_LR; \
+ _RB_MOD_XOR(gpar, _RB_LR); \
_RB_UP(parent, field) = gpar; \
gpar = _RB_PTR(gpar); \
continue; \
@@ -672,7 +678,7 @@ name##_RB_REMOVE_COLOR(struct name *head, \
sibdir = elmdir ^ _RB_LR; \
sib = _RB_LINK(parent, sibdir, field); \
up = _RB_UP(sib, field); \
- _RB_BITS(up) ^= _RB_LR; \
+ _RB_MOD_XOR(up, _RB_LR); \
if ((_RB_BITS(up) & _RB_LR) == 0) { \
/* shorten edges descending from sib, retry */ \
_RB_UP(sib, field) = up; \
@@ -703,24 +709,29 @@ name##_RB_REMOVE_COLOR(struct name *head, \
/* elm is a 1-child. First rotate at elm. */ \
RB_ROTATE(sib, elm, sibdir, field); \
up = _RB_UP(elm, field); \
- _RB_BITSUP(parent, field) ^= \
- (_RB_BITS(up) & elmdir) ? _RB_LR : elmdir; \
- _RB_BITSUP(sib, field) ^= \
- (_RB_BITS(up) & sibdir) ? _RB_LR : sibdir; \
- _RB_BITSUP(elm, field) |= _RB_LR; \
+ _RB_MOD_XOR(_RB_UP(parent, field), \
+ (_RB_BITS(up) & elmdir) ? _RB_LR : elmdir); \
+ _RB_MOD_XOR(_RB_UP(sib, field), \
+ (_RB_BITS(up) & sibdir) ? _RB_LR : sibdir); \
+ _RB_MOD_OR(_RB_UP(elm, field), _RB_LR); \
} else { \
if ((_RB_BITS(up) & elmdir) == 0 && \
RB_STRICT_HST && elm != NULL) { \
/* if parent does not become a leaf, \
do not demote parent yet. */ \
- _RB_BITSUP(parent, field) ^= sibdir; \
- _RB_BITSUP(sib, field) ^= _RB_LR; \
+ _RB_MOD_XOR(_RB_UP(parent, field), \
+ sibdir); \
+ _RB_MOD_XOR(_RB_UP(sib, field), \
+ _RB_LR); \
} else if ((_RB_BITS(up) & elmdir) == 0) { \
/* demote parent. */ \
- _RB_BITSUP(parent, field) ^= elmdir; \
- _RB_BITSUP(sib, field) ^= sibdir; \
+ _RB_MOD_XOR(_RB_UP(parent, field), \
+ elmdir); \
+ _RB_MOD_XOR(_RB_UP(sib, field), \
+ sibdir); \
} else \
- _RB_BITSUP(sib, field) ^= sibdir; \
+ _RB_MOD_XOR(_RB_UP(sib, field), \
+ sibdir); \
elm = sib; \
} \
\