1/*
2 * Copyright (C) 2011 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#ifndef ART_RUNTIME_MEMORY_REGION_H_
18#define ART_RUNTIME_MEMORY_REGION_H_
19
20#include <stdint.h>
21#include <type_traits>
22
23#include "arch/instruction_set.h"
24#include "base/bit_utils.h"
25#include "base/casts.h"
26#include "base/logging.h"
27#include "base/macros.h"
28#include "base/value_object.h"
29#include "globals.h"
30
31namespace art {
32
33// Memory regions are useful for accessing memory with bounds check in
34// debug mode. They can be safely passed by value and do not assume ownership
35// of the region.
36class MemoryRegion FINAL : public ValueObject {
37 public:
38  MemoryRegion() : pointer_(nullptr), size_(0) {}
39  MemoryRegion(void* pointer_in, uintptr_t size_in) : pointer_(pointer_in), size_(size_in) {}
40
41  void* pointer() const { return pointer_; }
42  size_t size() const { return size_; }
43  size_t size_in_bits() const { return size_ * kBitsPerByte; }
44
45  static size_t pointer_offset() {
46    return OFFSETOF_MEMBER(MemoryRegion, pointer_);
47  }
48
49  uint8_t* start() const { return reinterpret_cast<uint8_t*>(pointer_); }
50  uint8_t* end() const { return start() + size_; }
51
52  // Load value of type `T` at `offset`.  The memory address corresponding
53  // to `offset` should be word-aligned (on ARM, this is a requirement).
54  template<typename T>
55  ALWAYS_INLINE T Load(uintptr_t offset) const {
56    T* address = ComputeInternalPointer<T>(offset);
57    DCHECK(IsWordAligned(address));
58    return *address;
59  }
60
61  // Store `value` (of type `T`) at `offset`.  The memory address
62  // corresponding to `offset` should be word-aligned (on ARM, this is
63  // a requirement).
64  template<typename T>
65  ALWAYS_INLINE void Store(uintptr_t offset, T value) const {
66    T* address = ComputeInternalPointer<T>(offset);
67    DCHECK(IsWordAligned(address));
68    *address = value;
69  }
70
71  // Load value of type `T` at `offset`.  The memory address corresponding
72  // to `offset` does not need to be word-aligned.
73  template<typename T>
74  ALWAYS_INLINE T LoadUnaligned(uintptr_t offset) const {
75    // Equivalent unsigned integer type corresponding to T.
76    typedef typename std::make_unsigned<T>::type U;
77    U equivalent_unsigned_integer_value = 0;
78    // Read the value byte by byte in a little-endian fashion.
79    for (size_t i = 0; i < sizeof(U); ++i) {
80      equivalent_unsigned_integer_value +=
81          *ComputeInternalPointer<uint8_t>(offset + i) << (i * kBitsPerByte);
82    }
83    return bit_cast<T, U>(equivalent_unsigned_integer_value);
84  }
85
86  // Store `value` (of type `T`) at `offset`.  The memory address
87  // corresponding to `offset` does not need to be word-aligned.
88  template<typename T>
89  ALWAYS_INLINE void StoreUnaligned(uintptr_t offset, T value) const {
90    // Equivalent unsigned integer type corresponding to T.
91    typedef typename std::make_unsigned<T>::type U;
92    U equivalent_unsigned_integer_value = bit_cast<U, T>(value);
93    // Write the value byte by byte in a little-endian fashion.
94    for (size_t i = 0; i < sizeof(U); ++i) {
95      *ComputeInternalPointer<uint8_t>(offset + i) =
96          (equivalent_unsigned_integer_value >> (i * kBitsPerByte)) & 0xFF;
97    }
98  }
99
100  template<typename T>
101  ALWAYS_INLINE T* PointerTo(uintptr_t offset) const {
102    return ComputeInternalPointer<T>(offset);
103  }
104
105  // Load a single bit in the region. The bit at offset 0 is the least
106  // significant bit in the first byte.
107  ALWAYS_INLINE bool LoadBit(uintptr_t bit_offset) const {
108    uint8_t bit_mask;
109    uint8_t byte = *ComputeBitPointer(bit_offset, &bit_mask);
110    return byte & bit_mask;
111  }
112
113  ALWAYS_INLINE void StoreBit(uintptr_t bit_offset, bool value) const {
114    uint8_t bit_mask;
115    uint8_t* byte = ComputeBitPointer(bit_offset, &bit_mask);
116    if (value) {
117      *byte |= bit_mask;
118    } else {
119      *byte &= ~bit_mask;
120    }
121  }
122
123  // Load `length` bits from the region starting at bit offset `bit_offset`.
124  // The bit at the smallest offset is the least significant bit in the
125  // loaded value.  `length` must not be larger than the number of bits
126  // contained in the return value (32).
127  uint32_t LoadBits(uintptr_t bit_offset, size_t length) const {
128    CHECK_LE(length, sizeof(uint32_t) * kBitsPerByte);
129    uint32_t value = 0u;
130    for (size_t i = 0; i < length; ++i) {
131      value |= LoadBit(bit_offset + i) << i;
132    }
133    return value;
134  }
135
136  // Store `value` on `length` bits in the region starting at bit offset
137  // `bit_offset`.  The bit at the smallest offset is the least significant
138  // bit of the stored `value`.  `value` must not be larger than `length`
139  // bits.
140  void StoreBits(uintptr_t bit_offset, uint32_t value, size_t length) {
141    CHECK_LE(value, MaxInt<uint32_t>(length));
142    for (size_t i = 0; i < length; ++i) {
143      bool ith_bit = value & (1 << i);
144      StoreBit(bit_offset + i, ith_bit);
145    }
146  }
147
148  void CopyFrom(size_t offset, const MemoryRegion& from) const;
149
150  // Compute a sub memory region based on an existing one.
151  MemoryRegion Subregion(uintptr_t offset, uintptr_t size_in) const {
152    CHECK_GE(this->size(), size_in);
153    CHECK_LE(offset,  this->size() - size_in);
154    return MemoryRegion(reinterpret_cast<void*>(start() + offset), size_in);
155  }
156
157  // Compute an extended memory region based on an existing one.
158  void Extend(const MemoryRegion& region, uintptr_t extra) {
159    pointer_ = region.pointer();
160    size_ = (region.size() + extra);
161  }
162
163 private:
164  template<typename T>
165  ALWAYS_INLINE T* ComputeInternalPointer(size_t offset) const {
166    CHECK_GE(size(), sizeof(T));
167    CHECK_LE(offset, size() - sizeof(T));
168    return reinterpret_cast<T*>(start() + offset);
169  }
170
171  // Locate the bit with the given offset. Returns a pointer to the byte
172  // containing the bit, and sets bit_mask to the bit within that byte.
173  ALWAYS_INLINE uint8_t* ComputeBitPointer(uintptr_t bit_offset, uint8_t* bit_mask) const {
174    uintptr_t bit_remainder = (bit_offset & (kBitsPerByte - 1));
175    *bit_mask = (1U << bit_remainder);
176    uintptr_t byte_offset = (bit_offset >> kBitsPerByteLog2);
177    return ComputeInternalPointer<uint8_t>(byte_offset);
178  }
179
180  // Is `address` aligned on a machine word?
181  template<typename T> static bool IsWordAligned(const T* address) {
182    // Word alignment in bytes.
183    size_t kWordAlignment = GetInstructionSetPointerSize(kRuntimeISA);
184    return IsAlignedParam(address, kWordAlignment);
185  }
186
187  void* pointer_;
188  size_t size_;
189};
190
191}  // namespace art
192
193#endif  // ART_RUNTIME_MEMORY_REGION_H_
194