1 //===-- sanitizer_ring_buffer.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 // Simple ring buffer. 10 // 11 //===----------------------------------------------------------------------===// 12 #ifndef SANITIZER_RING_BUFFER_H 13 #define SANITIZER_RING_BUFFER_H 14 15 #include "sanitizer_common.h" 16 17 namespace __sanitizer { 18 // RingBuffer<T>: fixed-size ring buffer optimized for speed of push(). 19 // T should be a POD type and sizeof(T) should be divisible by sizeof(void*). 20 // At creation, all elements are zero. 21 template<class T> 22 class RingBuffer { 23 public: 24 COMPILER_CHECK(sizeof(T) % sizeof(void *) == 0); 25 static RingBuffer *New(uptr Size) { 26 void *Ptr = MmapOrDie(SizeInBytes(Size), "RingBuffer"); 27 RingBuffer *RB = reinterpret_cast<RingBuffer*>(Ptr); 28 uptr End = reinterpret_cast<uptr>(Ptr) + SizeInBytes(Size); 29 RB->last_ = RB->next_ = reinterpret_cast<T*>(End - sizeof(T)); 30 return RB; 31 } 32 void Delete() { 33 UnmapOrDie(this, SizeInBytes(size())); 34 } 35 uptr size() const { 36 return last_ + 1 - 37 reinterpret_cast<T *>(reinterpret_cast<uptr>(this) + 38 2 * sizeof(T *)); 39 } 40 41 static uptr SizeInBytes(uptr Size) { 42 return Size * sizeof(T) + 2 * sizeof(T*); 43 } 44 45 uptr SizeInBytes() { return SizeInBytes(size()); } 46 47 void push(T t) { 48 *next_ = t; 49 next_--; 50 // The condition below works only if sizeof(T) is divisible by sizeof(T*). 51 if (next_ <= reinterpret_cast<T*>(&next_)) 52 next_ = last_; 53 } 54 55 T operator[](uptr Idx) const { 56 CHECK_LT(Idx, size()); 57 sptr IdxNext = Idx + 1; 58 if (IdxNext > last_ - next_) 59 IdxNext -= size(); 60 return next_[IdxNext]; 61 } 62 63 private: 64 RingBuffer() {} 65 ~RingBuffer() {} 66 RingBuffer(const RingBuffer&) = delete; 67 68 // Data layout: 69 // LNDDDDDDDD 70 // D: data elements. 71 // L: last_, always points to the last data element. 72 // N: next_, initially equals to last_, is decremented on every push, 73 // wraps around if it's less or equal than its own address. 74 T *last_; 75 T *next_; 76 T data_[1]; // flexible array. 77 }; 78 79 // A ring buffer with externally provided storage that encodes its state in 8 80 // bytes. Has significant constraints on size and alignment of storage. 81 // See a comment in hwasan/hwasan_thread_list.h for the motivation behind this. 82 #if SANITIZER_WORDSIZE == 64 83 template <class T> 84 class CompactRingBuffer { 85 // Top byte of long_ stores the buffer size in pages. 86 // Lower bytes store the address of the next buffer element. 87 static constexpr int kPageSizeBits = 12; 88 static constexpr int kSizeShift = 56; 89 static constexpr uptr kNextMask = (1ULL << kSizeShift) - 1; 90 91 uptr GetStorageSize() const { return (long_ >> kSizeShift) << kPageSizeBits; } 92 93 void Init(void *storage, uptr size) { 94 CHECK_EQ(sizeof(CompactRingBuffer<T>), sizeof(void *)); 95 CHECK(IsPowerOfTwo(size)); 96 CHECK_GE(size, 1 << kPageSizeBits); 97 CHECK_LE(size, 128 << kPageSizeBits); 98 CHECK_EQ(size % 4096, 0); 99 CHECK_EQ(size % sizeof(T), 0); 100 CHECK_EQ((uptr)storage % (size * 2), 0); 101 long_ = (uptr)storage | ((size >> kPageSizeBits) << kSizeShift); 102 } 103 104 void SetNext(const T *next) { 105 long_ = (long_ & ~kNextMask) | (uptr)next; 106 } 107 108 public: 109 CompactRingBuffer(void *storage, uptr size) { 110 Init(storage, size); 111 } 112 113 // A copy constructor of sorts. 114 CompactRingBuffer(const CompactRingBuffer &other, void *storage) { 115 uptr size = other.GetStorageSize(); 116 internal_memcpy(storage, other.StartOfStorage(), size); 117 Init(storage, size); 118 uptr Idx = other.Next() - (const T *)other.StartOfStorage(); 119 SetNext((const T *)storage + Idx); 120 } 121 122 T *Next() const { return (T *)(long_ & kNextMask); } 123 124 void *StartOfStorage() const { 125 return (void *)((uptr)Next() & ~(GetStorageSize() - 1)); 126 } 127 128 void *EndOfStorage() const { 129 return (void *)((uptr)StartOfStorage() + GetStorageSize()); 130 } 131 132 uptr size() const { return GetStorageSize() / sizeof(T); } 133 134 void push(T t) { 135 T *next = Next(); 136 *next = t; 137 next++; 138 next = (T *)((uptr)next & ~GetStorageSize()); 139 SetNext(next); 140 } 141 142 const T &operator[](uptr Idx) const { 143 CHECK_LT(Idx, size()); 144 const T *Begin = (const T *)StartOfStorage(); 145 sptr StorageIdx = Next() - Begin; 146 StorageIdx -= (sptr)(Idx + 1); 147 if (StorageIdx < 0) 148 StorageIdx += size(); 149 return Begin[StorageIdx]; 150 } 151 152 public: 153 ~CompactRingBuffer() {} 154 CompactRingBuffer(const CompactRingBuffer &) = delete; 155 156 uptr long_; 157 }; 158 #endif 159 } // namespace __sanitizer 160 161 #endif // SANITIZER_RING_BUFFER_H 162