tagptr.h
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/* SPDX-License-Identifier: GPL-2.0-only */
/*
* A tagged pointer implementation
*
* Copyright (C) 2018 Gao Xiang <gaoxiang25@huawei.com>
*/
#ifndef __EROFS_FS_TAGPTR_H
#define __EROFS_FS_TAGPTR_H
#include <linux/types.h>
#include <linux/build_bug.h>
/*
* the name of tagged pointer types are tagptr{1, 2, 3...}_t
* avoid directly using the internal structs __tagptr{1, 2, 3...}
*/
#define __MAKE_TAGPTR(n) \
typedef struct __tagptr##n { \
uintptr_t v; \
} tagptr##n##_t;
__MAKE_TAGPTR(1)
__MAKE_TAGPTR(2)
__MAKE_TAGPTR(3)
__MAKE_TAGPTR(4)
#undef __MAKE_TAGPTR
extern void __compiletime_error("bad tagptr tags")
__bad_tagptr_tags(void);
extern void __compiletime_error("bad tagptr type")
__bad_tagptr_type(void);
/* fix the broken usage of "#define tagptr2_t tagptr3_t" by users */
#define __tagptr_mask_1(ptr, n) \
__builtin_types_compatible_p(typeof(ptr), struct __tagptr##n) ? \
(1UL << (n)) - 1 :
#define __tagptr_mask(ptr) (\
__tagptr_mask_1(ptr, 1) ( \
__tagptr_mask_1(ptr, 2) ( \
__tagptr_mask_1(ptr, 3) ( \
__tagptr_mask_1(ptr, 4) ( \
__bad_tagptr_type(), 0)))))
/* generate a tagged pointer from a raw value */
#define tagptr_init(type, val) \
((typeof(type)){ .v = (uintptr_t)(val) })
/*
* directly cast a tagged pointer to the native pointer type, which
* could be used for backward compatibility of existing code.
*/
#define tagptr_cast_ptr(tptr) ((void *)(tptr).v)
/* encode tagged pointers */
#define tagptr_fold(type, ptr, _tags) ({ \
const typeof(_tags) tags = (_tags); \
if (__builtin_constant_p(tags) && (tags & ~__tagptr_mask(type))) \
__bad_tagptr_tags(); \
tagptr_init(type, (uintptr_t)(ptr) | tags); })
/* decode tagged pointers */
#define tagptr_unfold_ptr(tptr) \
((void *)((tptr).v & ~__tagptr_mask(tptr)))
#define tagptr_unfold_tags(tptr) \
((tptr).v & __tagptr_mask(tptr))
/* operations for the tagger pointer */
#define tagptr_eq(_tptr1, _tptr2) ({ \
typeof(_tptr1) tptr1 = (_tptr1); \
typeof(_tptr2) tptr2 = (_tptr2); \
(void)(&tptr1 == &tptr2); \
(tptr1).v == (tptr2).v; })
/* lock-free CAS operation */
#define tagptr_cmpxchg(_ptptr, _o, _n) ({ \
typeof(_ptptr) ptptr = (_ptptr); \
typeof(_o) o = (_o); \
typeof(_n) n = (_n); \
(void)(&o == &n); \
(void)(&o == ptptr); \
tagptr_init(o, cmpxchg(&ptptr->v, o.v, n.v)); })
/* wrap WRITE_ONCE if atomic update is needed */
#define tagptr_replace_tags(_ptptr, tags) ({ \
typeof(_ptptr) ptptr = (_ptptr); \
*ptptr = tagptr_fold(*ptptr, tagptr_unfold_ptr(*ptptr), tags); \
*ptptr; })
#define tagptr_set_tags(_ptptr, _tags) ({ \
typeof(_ptptr) ptptr = (_ptptr); \
const typeof(_tags) tags = (_tags); \
if (__builtin_constant_p(tags) && (tags & ~__tagptr_mask(*ptptr))) \
__bad_tagptr_tags(); \
ptptr->v |= tags; \
*ptptr; })
#define tagptr_clear_tags(_ptptr, _tags) ({ \
typeof(_ptptr) ptptr = (_ptptr); \
const typeof(_tags) tags = (_tags); \
if (__builtin_constant_p(tags) && (tags & ~__tagptr_mask(*ptptr))) \
__bad_tagptr_tags(); \
ptptr->v &= ~tags; \
*ptptr; })
#endif /* __EROFS_FS_TAGPTR_H */