1 /* SPDX-License-Identifier: GPL-2.0 */ 1
2 /*
3 * Prevent the compiler from merging or refetc
4 * compiler is also forbidden from reordering
5 * READ_ONCE and WRITE_ONCE, but only when the
6 * particular ordering. One way to make the co
7 * put the two invocations of READ_ONCE or WRI
8 * statements.
9 *
10 * These two macros will also work on aggregat
11 * unions.
12 *
13 * Their two major use cases are: (1) Mediatin
14 * process-level code and irq/NMI handlers, al
15 * and (2) Ensuring that the compiler does not
16 * mutilate accesses that either do not requir
17 * with an explicit memory barrier or atomic i
18 * required ordering.
19 */
20 #ifndef __ASM_GENERIC_RWONCE_H
21 #define __ASM_GENERIC_RWONCE_H
22
23 #ifndef __ASSEMBLY__
24
25 #include <linux/compiler_types.h>
26 #include <linux/kasan-checks.h>
27 #include <linux/kcsan-checks.h>
28
29 /*
30 * Yes, this permits 64-bit accesses on 32-bit
31 * actually be atomic in some cases (namely Ar
32 * rely on the access being split into 2x32-bi
33 * (e.g. a virtual address) and a strong preva
34 */
35 #define compiletime_assert_rwonce_type(t)
36 compiletime_assert(__native_word(t) ||
37 "Unsupported access size for {
38
39 /*
40 * Use __READ_ONCE() instead of READ_ONCE() if
41 * atomicity. Note that this may result in tea
42 */
43 #ifndef __READ_ONCE
44 #define __READ_ONCE(x) (*(const volatile __un
45 #endif
46
47 #define READ_ONCE(x)
48 ({
49 compiletime_assert_rwonce_type(x);
50 __READ_ONCE(x);
51 })
52
53 #define __WRITE_ONCE(x, val)
54 do {
55 *(volatile typeof(x) *)&(x) = (val);
56 } while (0)
57
58 #define WRITE_ONCE(x, val)
59 do {
60 compiletime_assert_rwonce_type(x);
61 __WRITE_ONCE(x, val);
62 } while (0)
63
64 static __no_sanitize_or_inline
65 unsigned long __read_once_word_nocheck(const v
66 {
67 return __READ_ONCE(*(unsigned long *)a
68 }
69
70 /*
71 * Use READ_ONCE_NOCHECK() instead of READ_ONC
72 * word from memory atomically but without tel
73 * usually used by unwinding code when walking
74 */
75 #define READ_ONCE_NOCHECK(x)
76 ({
77 compiletime_assert(sizeof(x) == sizeof
78 "Unsupported access size for R
79 (typeof(x))__read_once_word_nocheck(&(
80 })
81
82 static __no_kasan_or_inline
83 unsigned long read_word_at_a_time(const void *
84 {
85 kasan_check_read(addr, 1);
86 return *(unsigned long *)addr;
87 }
88
89 #endif /* __ASSEMBLY__ */
90 #endif /* __ASM_GENERIC_RWONCE_H */
91
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