mem_map.cc revision 700a402244a1a423da4f3ba8032459f4b65fa18f
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#include "mem_map.h" 18 19#include <inttypes.h> 20#include <backtrace/BacktraceMap.h> 21#include <memory> 22 23#include "base/stringprintf.h" 24#include "ScopedFd.h" 25#include "utils.h" 26 27#define USE_ASHMEM 1 28 29#ifdef USE_ASHMEM 30#include <cutils/ashmem.h> 31#endif 32 33namespace art { 34 35static std::ostream& operator<<( 36 std::ostream& os, 37 std::pair<BacktraceMap::const_iterator, BacktraceMap::const_iterator> iters) { 38 for (BacktraceMap::const_iterator it = iters.first; it != iters.second; ++it) { 39 os << StringPrintf("0x%08x-0x%08x %c%c%c %s\n", 40 static_cast<uint32_t>(it->start), 41 static_cast<uint32_t>(it->end), 42 (it->flags & PROT_READ) ? 'r' : '-', 43 (it->flags & PROT_WRITE) ? 'w' : '-', 44 (it->flags & PROT_EXEC) ? 'x' : '-', it->name.c_str()); 45 } 46 return os; 47} 48 49#if defined(__LP64__) && !defined(__x86_64__) 50// Where to start with low memory allocation. The first 64KB is protected by SELinux. 51static constexpr uintptr_t LOW_MEM_START = 64 * KB; 52 53uintptr_t MemMap::next_mem_pos_ = LOW_MEM_START; // first page to check for low-mem extent 54#endif 55 56static bool CheckMapRequest(byte* expected_ptr, void* actual_ptr, size_t byte_count, 57 std::ostringstream* error_msg) { 58 // Handled first by caller for more specific error messages. 59 CHECK(actual_ptr != MAP_FAILED); 60 61 if (expected_ptr == nullptr) { 62 return true; 63 } 64 65 if (expected_ptr == actual_ptr) { 66 return true; 67 } 68 69 // We asked for an address but didn't get what we wanted, all paths below here should fail. 70 int result = munmap(actual_ptr, byte_count); 71 if (result == -1) { 72 PLOG(WARNING) << StringPrintf("munmap(%p, %zd) failed", actual_ptr, byte_count); 73 } 74 75 uintptr_t actual = reinterpret_cast<uintptr_t>(actual_ptr); 76 uintptr_t expected = reinterpret_cast<uintptr_t>(expected_ptr); 77 uintptr_t limit = expected + byte_count; 78 79 std::unique_ptr<BacktraceMap> map(BacktraceMap::Create(getpid())); 80 if (!map->Build()) { 81 *error_msg << StringPrintf("Failed to build process map to determine why mmap returned " 82 "0x%08" PRIxPTR " instead of 0x%08" PRIxPTR, actual, expected); 83 84 return false; 85 } 86 for (BacktraceMap::const_iterator it = map->begin(); it != map->end(); ++it) { 87 if ((expected >= it->start && expected < it->end) // start of new within old 88 || (limit > it->start && limit < it->end) // end of new within old 89 || (expected <= it->start && limit > it->end)) { // start/end of new includes all of old 90 *error_msg 91 << StringPrintf("Requested region 0x%08" PRIxPTR "-0x%08" PRIxPTR " overlaps with " 92 "existing map 0x%08" PRIxPTR "-0x%08" PRIxPTR " (%s)\n", 93 expected, limit, 94 static_cast<uintptr_t>(it->start), static_cast<uintptr_t>(it->end), 95 it->name.c_str()) 96 << std::make_pair(it, map->end()); 97 return false; 98 } 99 } 100 *error_msg << StringPrintf("Failed to mmap at expected address, mapped at " 101 "0x%08" PRIxPTR " instead of 0x%08" PRIxPTR, actual, expected); 102 return false; 103} 104 105MemMap* MemMap::MapAnonymous(const char* name, byte* expected, size_t byte_count, int prot, 106 bool low_4gb, std::string* error_msg) { 107 if (byte_count == 0) { 108 return new MemMap(name, nullptr, 0, nullptr, 0, prot); 109 } 110 size_t page_aligned_byte_count = RoundUp(byte_count, kPageSize); 111 112#ifdef USE_ASHMEM 113 // android_os_Debug.cpp read_mapinfo assumes all ashmem regions associated with the VM are 114 // prefixed "dalvik-". 115 std::string debug_friendly_name("dalvik-"); 116 debug_friendly_name += name; 117 ScopedFd fd(ashmem_create_region(debug_friendly_name.c_str(), page_aligned_byte_count)); 118 if (fd.get() == -1) { 119 *error_msg = StringPrintf("ashmem_create_region failed for '%s': %s", name, strerror(errno)); 120 return nullptr; 121 } 122 int flags = MAP_PRIVATE; 123#else 124 ScopedFd fd(-1); 125 int flags = MAP_PRIVATE | MAP_ANONYMOUS; 126#endif 127 128 // We need to store and potentially set an error number for pretty printing of errors 129 int saved_errno = 0; 130 131#ifdef __LP64__ 132 // When requesting low_4g memory and having an expectation, the requested range should fit into 133 // 4GB. 134 if (low_4gb && ( 135 // Start out of bounds. 136 (reinterpret_cast<uintptr_t>(expected) >> 32) != 0 || 137 // End out of bounds. For simplicity, this will fail for the last page of memory. 138 (reinterpret_cast<uintptr_t>(expected + page_aligned_byte_count) >> 32) != 0)) { 139 *error_msg = StringPrintf("The requested address space (%p, %p) cannot fit in low_4gb", 140 expected, expected + page_aligned_byte_count); 141 return nullptr; 142 } 143#endif 144 145 // TODO: 146 // A page allocator would be a useful abstraction here, as 147 // 1) It is doubtful that MAP_32BIT on x86_64 is doing the right job for us 148 // 2) The linear scheme, even with simple saving of the last known position, is very crude 149#if defined(__LP64__) && !defined(__x86_64__) 150 // MAP_32BIT only available on x86_64. 151 void* actual = MAP_FAILED; 152 if (low_4gb && expected == nullptr) { 153 flags |= MAP_FIXED; 154 155 bool first_run = true; 156 157 for (uintptr_t ptr = next_mem_pos_; ptr < 4 * GB; ptr += kPageSize) { 158 if (4U * GB - ptr < page_aligned_byte_count) { 159 // Not enough memory until 4GB. 160 if (first_run) { 161 // Try another time from the bottom; 162 ptr = LOW_MEM_START - kPageSize; 163 first_run = false; 164 continue; 165 } else { 166 // Second try failed. 167 break; 168 } 169 } 170 171 uintptr_t tail_ptr; 172 173 // Check pages are free. 174 bool safe = true; 175 for (tail_ptr = ptr; tail_ptr < ptr + page_aligned_byte_count; tail_ptr += kPageSize) { 176 if (msync(reinterpret_cast<void*>(tail_ptr), kPageSize, 0) == 0) { 177 safe = false; 178 break; 179 } else { 180 DCHECK_EQ(errno, ENOMEM); 181 } 182 } 183 184 next_mem_pos_ = tail_ptr; // update early, as we break out when we found and mapped a region 185 186 if (safe == true) { 187 actual = mmap(reinterpret_cast<void*>(ptr), page_aligned_byte_count, prot, flags, fd.get(), 188 0); 189 if (actual != MAP_FAILED) { 190 break; 191 } 192 } else { 193 // Skip over last page. 194 ptr = tail_ptr; 195 } 196 } 197 198 if (actual == MAP_FAILED) { 199 LOG(ERROR) << "Could not find contiguous low-memory space."; 200 saved_errno = ENOMEM; 201 } 202 } else { 203 actual = mmap(expected, page_aligned_byte_count, prot, flags, fd.get(), 0); 204 saved_errno = errno; 205 } 206 207#else 208#ifdef __x86_64__ 209 if (low_4gb && expected == nullptr) { 210 flags |= MAP_32BIT; 211 } 212#endif 213 214 void* actual = mmap(expected, page_aligned_byte_count, prot, flags, fd.get(), 0); 215 saved_errno = errno; 216#endif 217 218 if (actual == MAP_FAILED) { 219 std::string maps; 220 ReadFileToString("/proc/self/maps", &maps); 221 222 *error_msg = StringPrintf("Failed anonymous mmap(%p, %zd, 0x%x, 0x%x, %d, 0): %s\n%s", 223 expected, page_aligned_byte_count, prot, flags, fd.get(), 224 strerror(saved_errno), maps.c_str()); 225 return nullptr; 226 } 227 std::ostringstream check_map_request_error_msg; 228 if (!CheckMapRequest(expected, actual, page_aligned_byte_count, &check_map_request_error_msg)) { 229 *error_msg = check_map_request_error_msg.str(); 230 return nullptr; 231 } 232 return new MemMap(name, reinterpret_cast<byte*>(actual), byte_count, actual, 233 page_aligned_byte_count, prot); 234} 235 236MemMap* MemMap::MapFileAtAddress(byte* expected, size_t byte_count, int prot, int flags, int fd, 237 off_t start, bool reuse, const char* filename, 238 std::string* error_msg) { 239 CHECK_NE(0, prot); 240 CHECK_NE(0, flags & (MAP_SHARED | MAP_PRIVATE)); 241 if (reuse) { 242 // reuse means it is okay that it overlaps an existing page mapping. 243 // Only use this if you actually made the page reservation yourself. 244 CHECK(expected != nullptr); 245 flags |= MAP_FIXED; 246 } else { 247 CHECK_EQ(0, flags & MAP_FIXED); 248 } 249 250 if (byte_count == 0) { 251 return new MemMap(filename, nullptr, 0, nullptr, 0, prot); 252 } 253 // Adjust 'offset' to be page-aligned as required by mmap. 254 int page_offset = start % kPageSize; 255 off_t page_aligned_offset = start - page_offset; 256 // Adjust 'byte_count' to be page-aligned as we will map this anyway. 257 size_t page_aligned_byte_count = RoundUp(byte_count + page_offset, kPageSize); 258 // The 'expected' is modified (if specified, ie non-null) to be page aligned to the file but not 259 // necessarily to virtual memory. mmap will page align 'expected' for us. 260 byte* page_aligned_expected = (expected == nullptr) ? nullptr : (expected - page_offset); 261 262 byte* actual = reinterpret_cast<byte*>(mmap(page_aligned_expected, 263 page_aligned_byte_count, 264 prot, 265 flags, 266 fd, 267 page_aligned_offset)); 268 if (actual == MAP_FAILED) { 269 auto saved_errno = errno; 270 271 std::string maps; 272 ReadFileToString("/proc/self/maps", &maps); 273 274 *error_msg = StringPrintf("mmap(%p, %zd, 0x%x, 0x%x, %d, %" PRId64 275 ") of file '%s' failed: %s\n%s", 276 page_aligned_expected, page_aligned_byte_count, prot, flags, fd, 277 static_cast<int64_t>(page_aligned_offset), filename, 278 strerror(saved_errno), maps.c_str()); 279 return nullptr; 280 } 281 std::ostringstream check_map_request_error_msg; 282 if (!CheckMapRequest(expected, actual, page_aligned_byte_count, &check_map_request_error_msg)) { 283 *error_msg = check_map_request_error_msg.str(); 284 return nullptr; 285 } 286 return new MemMap(filename, actual + page_offset, byte_count, actual, page_aligned_byte_count, 287 prot); 288} 289 290MemMap::~MemMap() { 291 if (base_begin_ == nullptr && base_size_ == 0) { 292 return; 293 } 294 int result = munmap(base_begin_, base_size_); 295 if (result == -1) { 296 PLOG(FATAL) << "munmap failed"; 297 } 298} 299 300MemMap::MemMap(const std::string& name, byte* begin, size_t size, void* base_begin, 301 size_t base_size, int prot) 302 : name_(name), begin_(begin), size_(size), base_begin_(base_begin), base_size_(base_size), 303 prot_(prot) { 304 if (size_ == 0) { 305 CHECK(begin_ == nullptr); 306 CHECK(base_begin_ == nullptr); 307 CHECK_EQ(base_size_, 0U); 308 } else { 309 CHECK(begin_ != nullptr); 310 CHECK(base_begin_ != nullptr); 311 CHECK_NE(base_size_, 0U); 312 } 313}; 314 315MemMap* MemMap::RemapAtEnd(byte* new_end, const char* tail_name, int tail_prot, 316 std::string* error_msg) { 317 DCHECK_GE(new_end, Begin()); 318 DCHECK_LE(new_end, End()); 319 DCHECK_LE(begin_ + size_, reinterpret_cast<byte*>(base_begin_) + base_size_); 320 DCHECK(IsAligned<kPageSize>(begin_)); 321 DCHECK(IsAligned<kPageSize>(base_begin_)); 322 DCHECK(IsAligned<kPageSize>(reinterpret_cast<byte*>(base_begin_) + base_size_)); 323 DCHECK(IsAligned<kPageSize>(new_end)); 324 byte* old_end = begin_ + size_; 325 byte* old_base_end = reinterpret_cast<byte*>(base_begin_) + base_size_; 326 byte* new_base_end = new_end; 327 DCHECK_LE(new_base_end, old_base_end); 328 if (new_base_end == old_base_end) { 329 return new MemMap(tail_name, nullptr, 0, nullptr, 0, tail_prot); 330 } 331 size_ = new_end - reinterpret_cast<byte*>(begin_); 332 base_size_ = new_base_end - reinterpret_cast<byte*>(base_begin_); 333 DCHECK_LE(begin_ + size_, reinterpret_cast<byte*>(base_begin_) + base_size_); 334 size_t tail_size = old_end - new_end; 335 byte* tail_base_begin = new_base_end; 336 size_t tail_base_size = old_base_end - new_base_end; 337 DCHECK_EQ(tail_base_begin + tail_base_size, old_base_end); 338 DCHECK(IsAligned<kPageSize>(tail_base_size)); 339 340#ifdef USE_ASHMEM 341 // android_os_Debug.cpp read_mapinfo assumes all ashmem regions associated with the VM are 342 // prefixed "dalvik-". 343 std::string debug_friendly_name("dalvik-"); 344 debug_friendly_name += tail_name; 345 ScopedFd fd(ashmem_create_region(debug_friendly_name.c_str(), tail_base_size)); 346 int flags = MAP_PRIVATE | MAP_FIXED; 347 if (fd.get() == -1) { 348 *error_msg = StringPrintf("ashmem_create_region failed for '%s': %s", 349 tail_name, strerror(errno)); 350 return nullptr; 351 } 352#else 353 ScopedFd fd(-1); 354 int flags = MAP_PRIVATE | MAP_ANONYMOUS; 355#endif 356 357 // Unmap/map the tail region. 358 int result = munmap(tail_base_begin, tail_base_size); 359 if (result == -1) { 360 std::string maps; 361 ReadFileToString("/proc/self/maps", &maps); 362 *error_msg = StringPrintf("munmap(%p, %zd) failed for '%s'\n%s", 363 tail_base_begin, tail_base_size, name_.c_str(), 364 maps.c_str()); 365 return nullptr; 366 } 367 // Don't cause memory allocation between the munmap and the mmap 368 // calls. Otherwise, libc (or something else) might take this memory 369 // region. Note this isn't perfect as there's no way to prevent 370 // other threads to try to take this memory region here. 371 byte* actual = reinterpret_cast<byte*>(mmap(tail_base_begin, tail_base_size, tail_prot, 372 flags, fd.get(), 0)); 373 if (actual == MAP_FAILED) { 374 std::string maps; 375 ReadFileToString("/proc/self/maps", &maps); 376 *error_msg = StringPrintf("anonymous mmap(%p, %zd, 0x%x, 0x%x, %d, 0) failed\n%s", 377 tail_base_begin, tail_base_size, tail_prot, flags, fd.get(), 378 maps.c_str()); 379 return nullptr; 380 } 381 return new MemMap(tail_name, actual, tail_size, actual, tail_base_size, tail_prot); 382} 383 384bool MemMap::Protect(int prot) { 385 if (base_begin_ == nullptr && base_size_ == 0) { 386 prot_ = prot; 387 return true; 388 } 389 390 if (mprotect(base_begin_, base_size_, prot) == 0) { 391 prot_ = prot; 392 return true; 393 } 394 395 PLOG(ERROR) << "mprotect(" << reinterpret_cast<void*>(base_begin_) << ", " << base_size_ << ", " 396 << prot << ") failed"; 397 return false; 398} 399 400std::ostream& operator<<(std::ostream& os, const MemMap& mem_map) { 401 os << StringPrintf("[MemMap: %s prot=0x%x %p-%p]", 402 mem_map.GetName().c_str(), mem_map.GetProtect(), 403 mem_map.BaseBegin(), mem_map.BaseEnd()); 404 return os; 405} 406 407} // namespace art 408