mem_map.h revision a25dce9b452ba17ef7cef768926c884177a3025e 
1/*
2 * Copyright (C) 2008 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_MEM_MAP_H_
18#define ART_RUNTIME_MEM_MAP_H_
19
20#include "base/mutex.h"
21
22#include <string>
23#include <map>
24
25#include <stddef.h>
26#include <sys/mman.h>  // For the PROT_* and MAP_* constants.
27#include <sys/types.h>
28
29#include "base/allocator.h"
30#include "globals.h"
31
32namespace art {
33
34#if defined(__LP64__) && (!defined(__x86_64__) || defined(__APPLE__))
35#define USE_ART_LOW_4G_ALLOCATOR 1
36#else
37#define USE_ART_LOW_4G_ALLOCATOR 0
38#endif
39
40#ifdef __linux__
41static constexpr bool kMadviseZeroes = true;
42#else
43static constexpr bool kMadviseZeroes = false;
44#endif
45
46// Used to keep track of mmap segments.
47//
48// On 64b systems not supporting MAP_32BIT, the implementation of MemMap will do a linear scan
49// for free pages. For security, the start of this scan should be randomized. This requires a
50// dynamic initializer.
51// For this to work, it is paramount that there are no other static initializers that access MemMap.
52// Otherwise, calls might see uninitialized values.
53class MemMap {
54 public:
55  // Request an anonymous region of length 'byte_count' and a requested base address.
56  // Use null as the requested base address if you don't care.
57  // "reuse" allows re-mapping an address range from an existing mapping.
58  //
59  // The word "anonymous" in this context means "not backed by a file". The supplied
60  // 'name' will be used -- on systems that support it -- to give the mapping
61  // a name.
62  //
63  // On success, returns returns a MemMap instance.  On failure, returns null.
64  static MemMap* MapAnonymous(const char* name,
65                              uint8_t* addr,
66                              size_t byte_count,
67                              int prot,
68                              bool low_4gb,
69                              bool reuse,
70                              std::string* error_msg,
71                              bool use_ashmem = true);
72
73  // Create placeholder for a region allocated by direct call to mmap.
74  // This is useful when we do not have control over the code calling mmap,
75  // but when we still want to keep track of it in the list.
76  // The region is not considered to be owned and will not be unmmaped.
77  static MemMap* MapDummy(const char* name, uint8_t* addr, size_t byte_count);
78
79  // Map part of a file, taking care of non-page aligned offsets.  The
80  // "start" offset is absolute, not relative.
81  //
82  // On success, returns returns a MemMap instance.  On failure, returns null.
83  static MemMap* MapFile(size_t byte_count,
84                         int prot,
85                         int flags,
86                         int fd,
87                         off_t start,
88                         bool low_4gb,
89                         const char* filename,
90                         std::string* error_msg) {
91    return MapFileAtAddress(nullptr,
92                            byte_count,
93                            prot,
94                            flags,
95                            fd,
96                            start,
97                            /*low_4gb*/low_4gb,
98                            /*reuse*/false,
99                            filename,
100                            error_msg);
101  }
102
103  // Map part of a file, taking care of non-page aligned offsets.  The "start" offset is absolute,
104  // not relative. This version allows requesting a specific address for the base of the mapping.
105  // "reuse" allows us to create a view into an existing mapping where we do not take ownership of
106  // the memory. If error_msg is null then we do not print /proc/maps to the log if
107  // MapFileAtAddress fails. This helps improve performance of the fail case since reading and
108  // printing /proc/maps takes several milliseconds in the worst case.
109  //
110  // On success, returns returns a MemMap instance.  On failure, returns null.
111  static MemMap* MapFileAtAddress(uint8_t* addr,
112                                  size_t byte_count,
113                                  int prot,
114                                  int flags,
115                                  int fd,
116                                  off_t start,
117                                  bool low_4gb,
118                                  bool reuse,
119                                  const char* filename,
120                                  std::string* error_msg);
121
122  // Releases the memory mapping.
123  ~MemMap() REQUIRES(!Locks::mem_maps_lock_);
124
125  const std::string& GetName() const {
126    return name_;
127  }
128
129  bool Protect(int prot);
130
131  void MadviseDontNeedAndZero();
132
133  int GetProtect() const {
134    return prot_;
135  }
136
137  uint8_t* Begin() const {
138    return begin_;
139  }
140
141  size_t Size() const {
142    return size_;
143  }
144
145  // Resize the mem-map by unmapping pages at the end. Currently only supports shrinking.
146  void SetSize(size_t new_size);
147
148  uint8_t* End() const {
149    return Begin() + Size();
150  }
151
152  void* BaseBegin() const {
153    return base_begin_;
154  }
155
156  size_t BaseSize() const {
157    return base_size_;
158  }
159
160  void* BaseEnd() const {
161    return reinterpret_cast<uint8_t*>(BaseBegin()) + BaseSize();
162  }
163
164  bool HasAddress(const void* addr) const {
165    return Begin() <= addr && addr < End();
166  }
167
168  // Unmap the pages at end and remap them to create another memory map.
169  MemMap* RemapAtEnd(uint8_t* new_end,
170                     const char* tail_name,
171                     int tail_prot,
172                     std::string* error_msg,
173                     bool use_ashmem = true);
174
175  static bool CheckNoGaps(MemMap* begin_map, MemMap* end_map)
176      REQUIRES(!Locks::mem_maps_lock_);
177  static void DumpMaps(std::ostream& os, bool terse = false)
178      REQUIRES(!Locks::mem_maps_lock_);
179
180  typedef AllocationTrackingMultiMap<void*, MemMap*, kAllocatorTagMaps> Maps;
181
182  static void Init() REQUIRES(!Locks::mem_maps_lock_);
183  static void Shutdown() REQUIRES(!Locks::mem_maps_lock_);
184
185 private:
186  MemMap(const std::string& name,
187         uint8_t* begin,
188         size_t size,
189         void* base_begin,
190         size_t base_size,
191         int prot,
192         bool reuse,
193         size_t redzone_size = 0) REQUIRES(!Locks::mem_maps_lock_);
194
195  static void DumpMapsLocked(std::ostream& os, bool terse)
196      REQUIRES(Locks::mem_maps_lock_);
197  static bool HasMemMap(MemMap* map)
198      REQUIRES(Locks::mem_maps_lock_);
199  static MemMap* GetLargestMemMapAt(void* address)
200      REQUIRES(Locks::mem_maps_lock_);
201  static bool ContainedWithinExistingMap(uint8_t* ptr, size_t size, std::string* error_msg)
202      REQUIRES(!Locks::mem_maps_lock_);
203
204  // Internal version of mmap that supports low 4gb emulation.
205  static void* MapInternal(void* addr,
206                           size_t length,
207                           int prot,
208                           int flags,
209                           int fd,
210                           off_t offset,
211                           bool low_4gb);
212
213  const std::string name_;
214  uint8_t* const begin_;  // Start of data.
215  size_t size_;  // Length of data.
216
217  void* const base_begin_;  // Page-aligned base address.
218  size_t base_size_;  // Length of mapping. May be changed by RemapAtEnd (ie Zygote).
219  int prot_;  // Protection of the map.
220
221  // When reuse_ is true, this is just a view of an existing mapping
222  // and we do not take ownership and are not responsible for
223  // unmapping.
224  const bool reuse_;
225
226  const size_t redzone_size_;
227
228#if USE_ART_LOW_4G_ALLOCATOR
229  static uintptr_t next_mem_pos_;   // Next memory location to check for low_4g extent.
230#endif
231
232  // All the non-empty MemMaps. Use a multimap as we do a reserve-and-divide (eg ElfMap::Load()).
233  static Maps* maps_ GUARDED_BY(Locks::mem_maps_lock_);
234
235  friend class MemMapTest;  // To allow access to base_begin_ and base_size_.
236};
237std::ostream& operator<<(std::ostream& os, const MemMap& mem_map);
238std::ostream& operator<<(std::ostream& os, const MemMap::Maps& mem_maps);
239
240}  // namespace art
241
242#endif  // ART_RUNTIME_MEM_MAP_H_
243