| 1 | //===-- guarded_pool_allocator_tls.h ----------------------------*- C++ -*-===// |
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| 2 | // |
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| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
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| 4 | // See https://llvm.org/LICENSE.txt for license information. |
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| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
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| 6 | // |
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| 7 | //===----------------------------------------------------------------------===// |
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| 8 | |
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| 9 | #ifndef GWP_ASAN_GUARDED_POOL_ALLOCATOR_TLS_H_ |
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| 10 | #define GWP_ASAN_GUARDED_POOL_ALLOCATOR_TLS_H_ |
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| 11 | |
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| 12 | #include "gwp_asan/definitions.h" |
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| 13 | |
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| 14 | #include <stdint.h> |
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| 15 | |
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| 16 | namespace gwp_asan { |
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| 17 | // Pack the thread local variables into a struct to ensure that they're in |
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| 18 | // the same cache line for performance reasons. These are the most touched |
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| 19 | // variables in GWP-ASan. |
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| 20 | struct ThreadLocalPackedVariables { |
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| 21 | constexpr ThreadLocalPackedVariables() |
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| 22 | : RandomState(0xacd979ce), NextSampleCounter(0), RecursiveGuard(false) {} |
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| 23 | // Initialised to a magic constant so that an uninitialised GWP-ASan won't |
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| 24 | // regenerate its sample counter for as long as possible. The xorshift32() |
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| 25 | // algorithm used below results in getRandomUnsigned32(0xacd979ce) == |
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| 26 | // 0xfffffffe. |
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| 27 | uint32_t RandomState; |
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| 28 | // Thread-local decrementing counter that indicates that a given allocation |
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| 29 | // should be sampled when it reaches zero. |
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| 30 | uint32_t NextSampleCounter : 31; |
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| 31 | // The mask is needed to silence conversion errors. |
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| 32 | static const uint32_t NextSampleCounterMask = (1U << 31) - 1; |
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| 33 | // Guard against recursivity. Unwinders often contain complex behaviour that |
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| 34 | // may not be safe for the allocator (i.e. the unwinder calls dlopen(), |
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| 35 | // which calls malloc()). When recursive behaviour is detected, we will |
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| 36 | // automatically fall back to the supporting allocator to supply the |
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| 37 | // allocation. |
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| 38 | bool RecursiveGuard : 1; |
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| 39 | }; |
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| 40 | static_assert(sizeof(ThreadLocalPackedVariables) == sizeof(uint64_t), |
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| 41 | "thread local data does not fit in a uint64_t" ); |
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| 42 | } // namespace gwp_asan |
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| 43 | |
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| 44 | #ifdef GWP_ASAN_PLATFORM_TLS_HEADER |
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| 45 | #include GWP_ASAN_PLATFORM_TLS_HEADER |
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| 46 | #else |
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| 47 | namespace gwp_asan { |
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| 48 | inline ThreadLocalPackedVariables *getThreadLocals() { |
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| 49 | alignas(8) static GWP_ASAN_TLS_INITIAL_EXEC ThreadLocalPackedVariables Locals; |
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| 50 | return &Locals; |
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| 51 | } |
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| 52 | } // namespace gwp_asan |
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| 53 | #endif // GWP_ASAN_PLATFORM_TLS_HEADER |
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| 54 | |
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| 55 | #endif // GWP_ASAN_GUARDED_POOL_ALLOCATOR_TLS_H_ |
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| 56 | |
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