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/*
* Copyright 2018 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the OpenSSL license (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
*/
/*
* Goal here is to facilitate writing "thread-opportunistic" code that
* withstands Thread Sanitizer's scrutiny. "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-instuction
* 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.
*
* We utilize the fact that compilers that implement Thread Sanitizer
* implement even atomic operations. Then it's assumed that
* ATOMIC_{LONG|INT}_LOCK_FREE are assigned same value as
* ATOMIC_POINTER_LOCK_FREE. And check for >= 2 ensures that correspodning
* code is inlined. It should be noted that statistics counters become
* accurate in such case.
*/
#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)
# 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)
# endif
#elif defined(_MSC_VER) && _MSC_VER>=1200
# define TSAN_QUALIFIER volatile
# define tsan_load(ptr) (*(ptr))
# define tsan_store(ptr, val) (*(ptr) = (val))
# pragma intrinsic(_InterlockedExchangeAdd)
# ifdef _WIN64
# pragma intrinsic(_InterlockedExchangeAdd64)
# define tsan_counter(ptr) (sizeof(*ptr) == 8 ? _InterlockedExchangeAdd64((ptr), 1) \
: _InterlockedExchangeAdd((ptr), 1))
# else
# define tsan_counter(ptr) _InterlockedExchangeAdd((ptr), 1)
# 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))++)
#endif
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