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 
22 #include "base/logging.h"
23 #include "base/macros.h"
24 #include "globals.h"
25 
26 namespace art {
27 
28 // Memory regions are useful for accessing memory with bounds check in
29 // debug mode. They can be safely passed by value and do not assume ownership
30 // of the region.
31 class MemoryRegion {
32  public:
MemoryRegion()33   MemoryRegion() : pointer_(NULL), size_(0) {}
MemoryRegion(void * pointer,uword size)34   MemoryRegion(void* pointer, uword size) : pointer_(pointer), size_(size) {}
35 
pointer()36   void* pointer() const { return pointer_; }
size()37   size_t size() const { return size_; }
size_in_bits()38   size_t size_in_bits() const { return size_ * kBitsPerByte; }
39 
pointer_offset()40   static size_t pointer_offset() {
41     return OFFSETOF_MEMBER(MemoryRegion, pointer_);
42   }
43 
start()44   byte* start() const { return reinterpret_cast<byte*>(pointer_); }
end()45   byte* end() const { return start() + size_; }
46 
Load(uintptr_t offset)47   template<typename T> T Load(uintptr_t offset) const {
48     return *ComputeInternalPointer<T>(offset);
49   }
50 
Store(uintptr_t offset,T value)51   template<typename T> void Store(uintptr_t offset, T value) const {
52     *ComputeInternalPointer<T>(offset) = value;
53   }
54 
PointerTo(uintptr_t offset)55   template<typename T> T* PointerTo(uintptr_t offset) const {
56     return ComputeInternalPointer<T>(offset);
57   }
58 
59   // Load a single bit in the region. The bit at offset 0 is the least
60   // significant bit in the first byte.
LoadBit(uintptr_t bit_offset)61   bool LoadBit(uintptr_t bit_offset) const {
62     uint8_t bit_mask;
63     uint8_t byte = *ComputeBitPointer(bit_offset, &bit_mask);
64     return byte & bit_mask;
65   }
66 
StoreBit(uintptr_t bit_offset,bool value)67   void StoreBit(uintptr_t bit_offset, bool value) const {
68     uint8_t bit_mask;
69     uint8_t* byte = ComputeBitPointer(bit_offset, &bit_mask);
70     if (value) {
71       *byte |= bit_mask;
72     } else {
73       *byte &= ~bit_mask;
74     }
75   }
76 
77   void CopyFrom(size_t offset, const MemoryRegion& from) const;
78 
79   // Compute a sub memory region based on an existing one.
Subregion(uintptr_t offset,uintptr_t size)80   MemoryRegion Subregion(uintptr_t offset, uintptr_t size) const {
81     CHECK_GE(this->size(), size);
82     CHECK_LE(offset,  this->size() - size);
83     return MemoryRegion(reinterpret_cast<void*>(start() + offset), size);
84   }
85 
86   // Compute an extended memory region based on an existing one.
Extend(const MemoryRegion & region,uintptr_t extra)87   void Extend(const MemoryRegion& region, uintptr_t extra) {
88     pointer_ = region.pointer();
89     size_ = (region.size() + extra);
90   }
91 
92  private:
ComputeInternalPointer(size_t offset)93   template<typename T> T* ComputeInternalPointer(size_t offset) const {
94     CHECK_GE(size(), sizeof(T));
95     CHECK_LE(offset, size() - sizeof(T));
96     return reinterpret_cast<T*>(start() + offset);
97   }
98 
99   // Locate the bit with the given offset. Returns a pointer to the byte
100   // containing the bit, and sets bit_mask to the bit within that byte.
ComputeBitPointer(uintptr_t bit_offset,byte * bit_mask)101   byte* ComputeBitPointer(uintptr_t bit_offset, byte* bit_mask) const {
102     uintptr_t bit_remainder = (bit_offset & (kBitsPerByte - 1));
103     *bit_mask = (1U << bit_remainder);
104     uintptr_t byte_offset = (bit_offset >> kBitsPerByteLog2);
105     return ComputeInternalPointer<byte>(byte_offset);
106   }
107 
108   void* pointer_;
109   size_t size_;
110 };
111 
112 }  // namespace art
113 
114 #endif  // ART_RUNTIME_MEMORY_REGION_H_
115