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