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/*
* Copyright 2018 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the Apache License 2.0 (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
/*
* Contemporary compilers implement lock-free atomic memory access
* primitives that facilitate writing "thread-opportunistic" or even real
* multi-threading low-overhead code. "Thread-opportunistic" is when
* exact result is not required, e.g. some statistics, or execution flow
* doesn't have to be unambiguous. Simplest example is lazy "constant"
* initialization when one can synchronize on variable itself, e.g.
*
* if (var == NOT_YET_INITIALIZED)
* var = function_returning_same_value();
*
* This does work provided that loads and stores are single-instruction
* operations (and integer ones are on *all* supported platforms), but
* it upsets Thread Sanitizer. Suggested solution is
*
* if (tsan_load(&var) == NOT_YET_INITIALIZED)
* tsan_store(&var, function_returning_same_value());
*
* Production machine code would be the same, so one can wonder why
* bother. Having Thread Sanitizer accept "thread-opportunistic" code
* allows to move on trouble-shooting real bugs.
*
* Resolving Thread Sanitizer nits was the initial purpose for this module,
* but it was later extended with more nuanced primitives that are useful
* even in "non-opportunistic" scenarios. Most notably verifying if a shared
* structure is fully initialized and bypassing the initialization lock.
* It's suggested to view macros defined in this module as "annotations" for
* thread-safe lock-free code, "Thread-Safe ANnotations"...
*
* It's assumed that ATOMIC_{LONG|INT}_LOCK_FREE are assigned same value as
* ATOMIC_POINTER_LOCK_FREE. And check for >= 2 ensures that corresponding
* code is inlined. It should be noted that statistics counters become
* accurate in such case.
*
* Special note about TSAN_QUALIFIER. It might be undesired to use it in
* a shared header. Because whether operation on specific variable or member
* is atomic or not might be irrelevant in other modules. In such case one
* can use TSAN_QUALIFIER in cast specifically when it has to count.
*/
#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L \
&& !defined(__STDC_NO_ATOMICS__)
# include <stdatomic.h>
# if defined(ATOMIC_POINTER_LOCK_FREE) \
&& ATOMIC_POINTER_LOCK_FREE >= 2
# define TSAN_QUALIFIER _Atomic
# define tsan_load(ptr) atomic_load_explicit((ptr), memory_order_relaxed)
# define tsan_store(ptr, val) atomic_store_explicit((ptr), (val), memory_order_relaxed)
# define tsan_counter(ptr) atomic_fetch_add_explicit((ptr), 1, memory_order_relaxed)
# define tsan_decr(ptr) atomic_fetch_add_explicit((ptr), -1, memory_order_relaxed)
# define tsan_ld_acq(ptr) atomic_load_explicit((ptr), memory_order_acquire)
# define tsan_st_rel(ptr, val) atomic_store_explicit((ptr), (val), memory_order_release)
# endif
#elif defined(__GNUC__) && defined(__ATOMIC_RELAXED)
# if defined(__GCC_ATOMIC_POINTER_LOCK_FREE) \
&& __GCC_ATOMIC_POINTER_LOCK_FREE >= 2
# define TSAN_QUALIFIER volatile
# define tsan_load(ptr) __atomic_load_n((ptr), __ATOMIC_RELAXED)
# define tsan_store(ptr, val) __atomic_store_n((ptr), (val), __ATOMIC_RELAXED)
# define tsan_counter(ptr) __atomic_fetch_add((ptr), 1, __ATOMIC_RELAXED)
# define tsan_decr(ptr) __atomic_fetch_add((ptr), -1, __ATOMIC_RELAXED)
# define tsan_ld_acq(ptr) __atomic_load_n((ptr), __ATOMIC_ACQUIRE)
# define tsan_st_rel(ptr, val) __atomic_store_n((ptr), (val), __ATOMIC_RELEASE)
# endif
#elif defined(_MSC_VER) && _MSC_VER>=1200 \
&& (defined(_M_IX86) || defined(_M_AMD64) || defined(_M_X64) || \
defined(_M_ARM64) || (defined(_M_ARM) && _M_ARM >= 7 && !defined(_WIN32_WCE)))
/*
* There is subtle dependency on /volatile:<iso|ms> command-line option.
* "ms" implies same semantic as memory_order_acquire for loads and
* memory_order_release for stores, while "iso" - memory_order_relaxed for
* either. Real complication is that defaults are different on x86 and ARM.
* There is explanation for that, "ms" is backward compatible with earlier
* compiler versions, while multi-processor ARM can be viewed as brand new
* platform to MSC and its users, and with non-relaxed semantic taking toll
* with additional instructions and penalties, it kind of makes sense to
* default to "iso"...
*/
# define TSAN_QUALIFIER volatile
# if defined(_M_ARM) || defined(_M_ARM64)
# define _InterlockedExchangeAdd _InterlockedExchangeAdd_nf
# pragma intrinsic(_InterlockedExchangeAdd_nf)
# pragma intrinsic(__iso_volatile_load32, __iso_volatile_store32)
# ifdef _WIN64
# define _InterlockedExchangeAdd64 _InterlockedExchangeAdd64_nf
# pragma intrinsic(_InterlockedExchangeAdd64_nf)
# pragma intrinsic(__iso_volatile_load64, __iso_volatile_store64)
# define tsan_load(ptr) (sizeof(*(ptr)) == 8 ? __iso_volatile_load64(ptr) \
: __iso_volatile_load32(ptr))
# define tsan_store(ptr, val) (sizeof(*(ptr)) == 8 ? __iso_volatile_store64((ptr), (val)) \
: __iso_volatile_store32((ptr), (val)))
# else
# define tsan_load(ptr) __iso_volatile_load32(ptr)
# define tsan_store(ptr, val) __iso_volatile_store32((ptr), (val))
# endif
# else
# define tsan_load(ptr) (*(ptr))
# define tsan_store(ptr, val) (*(ptr) = (val))
# endif
# pragma intrinsic(_InterlockedExchangeAdd)
# ifdef _WIN64
# pragma intrinsic(_InterlockedExchangeAdd64)
# define tsan_counter(ptr) (sizeof(*(ptr)) == 8 ? _InterlockedExchangeAdd64((ptr), 1) \
: _InterlockedExchangeAdd((ptr), 1))
# define tsan_decr(ptr) (sizeof(*(ptr)) == 8 ? _InterlockedExchangeAdd64((ptr), -1) \
: _InterlockedExchangeAdd((ptr), -1))
# else
# define tsan_counter(ptr) _InterlockedExchangeAdd((ptr), 1)
# define tsan_decr(ptr) _InterlockedExchangeAdd((ptr), -1)
# endif
# if !defined(_ISO_VOLATILE)
# define tsan_ld_acq(ptr) (*(ptr))
# define tsan_st_rel(ptr, val) (*(ptr) = (val))
# endif
#endif
#ifndef TSAN_QUALIFIER
# define TSAN_QUALIFIER volatile
# define tsan_load(ptr) (*(ptr))
# define tsan_store(ptr, val) (*(ptr) = (val))
# define tsan_counter(ptr) ((*(ptr))++)
# define tsan_decr(ptr) ((*(ptr))--)
/*
* Lack of tsan_ld_acq and tsan_ld_rel means that compiler support is not
* sophisticated enough to support them. Code that relies on them should be
* protected with #ifdef tsan_ld_acq with locked fallback.
*/
#endif
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