1/*
2 * Copyright 2018 The OpenSSL Project Authors. All Rights Reserved.
3 *
4 * Licensed under the Apache License 2.0 (the "License"). You may not use
5 * this file except in compliance with the License. You can obtain a copy
6 * in the file LICENSE in the source distribution or at
7 * https://www.openssl.org/source/license.html
8 */
9
10/*
11 * Contemporary compilers implement lock-free atomic memory access
12 * primitives that facilitate writing "thread-opportunistic" or even real
13 * multi-threading low-overhead code. "Thread-opportunistic" is when
14 * exact result is not required, e.g. some statistics, or execution flow
15 * doesn't have to be unambiguous. Simplest example is lazy "constant"
16 * initialization when one can synchronize on variable itself, e.g.
17 *
18 * if (var == NOT_YET_INITIALIZED)
19 * var = function_returning_same_value();
20 *
21 * This does work provided that loads and stores are single-instruction
22 * operations (and integer ones are on *all* supported platforms), but
23 * it upsets Thread Sanitizer. Suggested solution is
24 *
25 * if (tsan_load(&var) == NOT_YET_INITIALIZED)
26 * tsan_store(&var, function_returning_same_value());
27 *
28 * Production machine code would be the same, so one can wonder why
29 * bother. Having Thread Sanitizer accept "thread-opportunistic" code
30 * allows to move on trouble-shooting real bugs.
31 *
32 * Resolving Thread Sanitizer nits was the initial purpose for this module,
33 * but it was later extended with more nuanced primitives that are useful
34 * even in "non-opportunistic" scenarios. Most notably verifying if a shared
35 * structure is fully initialized and bypassing the initialization lock.
36 * It's suggested to view macros defined in this module as "annotations" for
37 * thread-safe lock-free code, "Thread-Safe ANnotations"...
38 *
39 * It's assumed that ATOMIC_{LONG|INT}_LOCK_FREE are assigned same value as
40 * ATOMIC_POINTER_LOCK_FREE. And check for >= 2 ensures that corresponding
41 * code is inlined. It should be noted that statistics counters become
42 * accurate in such case.
43 *
44 * Special note about TSAN_QUALIFIER. It might be undesired to use it in
45 * a shared header. Because whether operation on specific variable or member
46 * is atomic or not might be irrelevant in other modules. In such case one
47 * can use TSAN_QUALIFIER in cast specifically when it has to count.
48 */
49
50#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L \
51 && !defined(__STDC_NO_ATOMICS__)
52# include <stdatomic.h>
53
54# if defined(ATOMIC_POINTER_LOCK_FREE) \
55 && ATOMIC_POINTER_LOCK_FREE >= 2
56# define TSAN_QUALIFIER _Atomic
57# define tsan_load(ptr) atomic_load_explicit((ptr), memory_order_relaxed)
58# define tsan_store(ptr, val) atomic_store_explicit((ptr), (val), memory_order_relaxed)
59# define tsan_counter(ptr) atomic_fetch_add_explicit((ptr), 1, memory_order_relaxed)
60# define tsan_decr(ptr) atomic_fetch_add_explicit((ptr), -1, memory_order_relaxed)
61# define tsan_ld_acq(ptr) atomic_load_explicit((ptr), memory_order_acquire)
62# define tsan_st_rel(ptr, val) atomic_store_explicit((ptr), (val), memory_order_release)
63# endif
64
65#elif defined(__GNUC__) && defined(__ATOMIC_RELAXED)
66
67# if defined(__GCC_ATOMIC_POINTER_LOCK_FREE) \
68 && __GCC_ATOMIC_POINTER_LOCK_FREE >= 2
69# define TSAN_QUALIFIER volatile
70# define tsan_load(ptr) __atomic_load_n((ptr), __ATOMIC_RELAXED)
71# define tsan_store(ptr, val) __atomic_store_n((ptr), (val), __ATOMIC_RELAXED)
72# define tsan_counter(ptr) __atomic_fetch_add((ptr), 1, __ATOMIC_RELAXED)
73# define tsan_decr(ptr) __atomic_fetch_add((ptr), -1, __ATOMIC_RELAXED)
74# define tsan_ld_acq(ptr) __atomic_load_n((ptr), __ATOMIC_ACQUIRE)
75# define tsan_st_rel(ptr, val) __atomic_store_n((ptr), (val), __ATOMIC_RELEASE)
76# endif
77
78#elif defined(_MSC_VER) && _MSC_VER>=1200 \
79 && (defined(_M_IX86) || defined(_M_AMD64) || defined(_M_X64) || \
80 defined(_M_ARM64) || (defined(_M_ARM) && _M_ARM >= 7 && !defined(_WIN32_WCE)))
81/*
82 * There is subtle dependency on /volatile:<iso|ms> command-line option.
83 * "ms" implies same semantic as memory_order_acquire for loads and
84 * memory_order_release for stores, while "iso" - memory_order_relaxed for
85 * either. Real complication is that defaults are different on x86 and ARM.
86 * There is explanation for that, "ms" is backward compatible with earlier
87 * compiler versions, while multi-processor ARM can be viewed as brand new
88 * platform to MSC and its users, and with non-relaxed semantic taking toll
89 * with additional instructions and penalties, it kind of makes sense to
90 * default to "iso"...
91 */
92# define TSAN_QUALIFIER volatile
93# if defined(_M_ARM) || defined(_M_ARM64)
94# define _InterlockedExchangeAdd _InterlockedExchangeAdd_nf
95# pragma intrinsic(_InterlockedExchangeAdd_nf)
96# pragma intrinsic(__iso_volatile_load32, __iso_volatile_store32)
97# ifdef _WIN64
98# define _InterlockedExchangeAdd64 _InterlockedExchangeAdd64_nf
99# pragma intrinsic(_InterlockedExchangeAdd64_nf)
100# pragma intrinsic(__iso_volatile_load64, __iso_volatile_store64)
101# define tsan_load(ptr) (sizeof(*(ptr)) == 8 ? __iso_volatile_load64(ptr) \
102 : __iso_volatile_load32(ptr))
103# define tsan_store(ptr, val) (sizeof(*(ptr)) == 8 ? __iso_volatile_store64((ptr), (val)) \
104 : __iso_volatile_store32((ptr), (val)))
105# else
106# define tsan_load(ptr) __iso_volatile_load32(ptr)
107# define tsan_store(ptr, val) __iso_volatile_store32((ptr), (val))
108# endif
109# else
110# define tsan_load(ptr) (*(ptr))
111# define tsan_store(ptr, val) (*(ptr) = (val))
112# endif
113# pragma intrinsic(_InterlockedExchangeAdd)
114# ifdef _WIN64
115# pragma intrinsic(_InterlockedExchangeAdd64)
116# define tsan_counter(ptr) (sizeof(*(ptr)) == 8 ? _InterlockedExchangeAdd64((ptr), 1) \
117 : _InterlockedExchangeAdd((ptr), 1))
118# define tsan_decr(ptr) (sizeof(*(ptr)) == 8 ? _InterlockedExchangeAdd64((ptr), -1) \
119 : _InterlockedExchangeAdd((ptr), -1))
120# else
121# define tsan_counter(ptr) _InterlockedExchangeAdd((ptr), 1)
122# define tsan_decr(ptr) _InterlockedExchangeAdd((ptr), -1)
123# endif
124# if !defined(_ISO_VOLATILE)
125# define tsan_ld_acq(ptr) (*(ptr))
126# define tsan_st_rel(ptr, val) (*(ptr) = (val))
127# endif
128
129#endif
130
131#ifndef TSAN_QUALIFIER
132
133# define TSAN_QUALIFIER volatile
134# define tsan_load(ptr) (*(ptr))
135# define tsan_store(ptr, val) (*(ptr) = (val))
136# define tsan_counter(ptr) ((*(ptr))++)
137# define tsan_decr(ptr) ((*(ptr))--)
138/*
139 * Lack of tsan_ld_acq and tsan_ld_rel means that compiler support is not
140 * sophisticated enough to support them. Code that relies on them should be
141 * protected with #ifdef tsan_ld_acq with locked fallback.
142 */
143
144#endif
145