1 Malloc Debug 2 ============ 3 4 Malloc debug is a method of debugging native memory problems. It can help 5 detect memory corruption, memory leaks, and use after free issues. 6 7 This documentation describes how to enable this feature on Android N or later 8 versions of the Android OS. (See the "Examples" section.) 9 10 The documentation for malloc debug on older versions of Android is 11 [here](README_marshmallow_and_earlier.md). 12 13 When malloc debug is enabled, it works by adding a shim layer that replaces 14 the normal allocation calls. The replaced calls are: 15 16 * `malloc` 17 * `free` 18 * `calloc` 19 * `realloc` 20 * `posix_memalign` 21 * `memalign` 22 * `aligned_alloc` 23 * `malloc_usable_size` 24 25 On 32 bit systems, these two deprecated functions are also replaced: 26 27 * `pvalloc` 28 * `valloc` 29 30 Any errors detected by the library are reported in the log. 31 32 NOTE: There is a small behavioral change beginning in P for realloc. 33 Before, a realloc from one size to a smaller size would not update the 34 backtrace related to the allocation. Starting in P, every single realloc 35 call changes the backtrace for the pointer no matter whether the pointer 36 returned has changed or not. 37 38 39 Controlling Malloc Debug Behavior 40 --------------------------------- 41 Malloc debug is controlled by individual options. Each option can be enabled 42 individually, or in a group of other options. Every single option can be 43 combined with every other option. 44 45 Option Descriptions 46 ------------------- 47 ### front\_guard[=SIZE\_BYTES] 48 Enables a small buffer placed before the allocated data. This is an attempt 49 to find memory corruption occuring to a region before the original allocation. 50 On first allocation, this front guard is written with a specific pattern (0xaa). 51 When the allocation is freed, the guard is checked to verify it has not been 52 modified. If any part of the front guard is modified, an error will be reported 53 in the log indicating what bytes changed. 54 55 If the backtrace option is also enabled, then any error message will include 56 the backtrace of the allocation site. 57 58 If SIZE\_BYTES is present, it indicates the number of bytes in the guard. 59 The default is 32 bytes, the max bytes is 16384. SIZE\_BYTES will be 60 padded so that it is a multiple of 8 bytes on 32 bit systems and 16 bytes 61 on 64 bit systems to make sure that the allocation returned is aligned 62 properly. 63 64 This option adds a special header to all allocations that contains the guard 65 and information about the original allocation. 66 67 Example error: 68 69 04-10 12:00:45.621 7412 7412 E malloc_debug: +++ ALLOCATION 0x12345678 SIZE 100 HAS A CORRUPTED FRONT GUARD 70 04-10 12:00:45.622 7412 7412 E malloc_debug: allocation[-32] = 0x00 (expected 0xaa) 71 04-10 12:00:45.622 7412 7412 E malloc_debug: allocation[-15] = 0x02 (expected 0xaa) 72 73 ### rear\_guard[=SIZE\_BYTES] 74 Enables a small buffer placed after the allocated data. This is an attempt 75 to find memory corruption occuring to a region after the original allocation. 76 On first allocation, this rear guard is written with a specific pattern (0xbb). 77 When the allocation is freed, the guard is checked to verify it has not been 78 modified. If any part of the rear guard is modified, an error will be reported 79 in the log indicating what bytes changed. 80 81 If SIZE\_BYTES is present, it indicates the number of bytes in the guard. 82 The default is 32 bytes, the max bytes is 16384. 83 84 This option adds a special header to all allocations that contains 85 information about the original allocation. 86 87 Example error: 88 89 04-10 12:00:45.621 7412 7412 E malloc_debug: +++ ALLOCATION 0x12345678 SIZE 100 HAS A CORRUPTED REAR GUARD 90 04-10 12:00:45.622 7412 7412 E malloc_debug: allocation[130] = 0xbf (expected 0xbb) 91 04-10 12:00:45.622 7412 7412 E malloc_debug: allocation[131] = 0x00 (expected 0xbb) 92 93 ### guard[=SIZE\_BYTES] 94 Enables both a front guard and a rear guard on all allocations. 95 96 If SIZE\_BYTES is present, it indicates the number of bytes in both guards. 97 The default is 32 bytes, the max bytes is 16384. 98 99 ### backtrace[=MAX\_FRAMES] 100 Enable capturing the backtrace of each allocation site. 101 This option will slow down allocations by an order of magnitude. If the 102 system runs too slowly with this option enabled, decreasing the maximum number 103 of frames captured will speed the allocations up. 104 105 Note that any backtrace frames that occur within the malloc backtrace library 106 itself are not recorded. 107 108 If MAX\_FRAMES is present, it indicates the maximum number of frames to 109 capture in a backtrace. The default is 16 frames, the maximumum value 110 this can be set to is 256. 111 112 Before P, this option adds a special header to all allocations that contains 113 the backtrace and information about the original allocation. After that, this 114 option will not add a special header. 115 116 As of P, this option will also enable dumping backtrace heap data to a 117 file when the process receives the signal SIGRTMAX - 17 ( which is 47 on most 118 Android devices). The format of this dumped data is the same format as 119 that dumped when running am dumpheap -n. The default is to dump this data 120 to the file /data/local/tmp/backtrace\_heap.**PID**.txt. This is useful when 121 used with native only executables that run for a while since these processes 122 are not spawned from a zygote process. 123 124 Note that when the signal is received, the heap is not dumped until the next 125 malloc/free occurs. 126 127 ### backtrace\_enable\_on\_signal[=MAX\_FRAMES] 128 Enable capturing the backtrace of each allocation site. If the 129 backtrace capture is toggled when the process receives the signal 130 SIGRTMAX - 19 (which is 45 on most Android devices). When this 131 option is used alone, backtrace capture starts out disabled until the signal 132 is received. If both this option and the backtrace option are set, then 133 backtrace capture is enabled until the signal is received. 134 135 If MAX\_FRAMES is present, it indicates the maximum number of frames to 136 capture in a backtrace. The default is 16 frames, the maximumum value 137 this can be set to is 256. 138 139 Before P, this option adds a special header to all allocations that contains 140 the backtrace and information about the original allocation. After that, this 141 option will not add a special header. 142 143 ### backtrace\_dump\_on\_exit 144 As of P, when the backtrace option has been enabled, this causes the backtrace 145 dump heap data to be dumped to a file when the program exits. If the backtrace 146 option has not been enabled, this does nothing. The default is to dump this 147 to the file named /data/local/tmp/backtrace\_heap.**PID**.exit.txt. 148 149 The file location can be changed by setting the backtrace\_dump\_prefix 150 option. 151 152 ### backtrace\_dump\_prefix 153 As of P, when one of the backtrace options has been enabled, this sets the 154 prefix used for dumping files when the signal SIGRTMAX - 17 is received or when 155 the program exits and backtrace\_dump\_on\_exit is set. 156 157 The default is /data/local/tmp/backtrace\_heap. 158 159 When this value is changed from the default, then the filename chosen 160 on the signal will be backtrace\_dump\_prefix.**PID**.txt. The filename chosen 161 when the program exits will be backtrace\_dump\_prefix.**PID**.exit.txt. 162 163 ### backtrace\_full 164 As of Q, any time that a backtrace is gathered, a different algorithm is used 165 that is extra thorough and can unwind through Java frames. This will run 166 slower than the normal backtracing function. 167 168 ### fill\_on\_alloc[=MAX\_FILLED\_BYTES] 169 Any allocation routine, other than calloc, will result in the allocation being 170 filled with the value 0xeb. When doing a realloc to a larger size, the bytes 171 above the original usable size will be set to 0xeb. 172 173 If MAX\_FILLED\_BYTES is present, it will only fill up to the specified number 174 of bytes in the allocation. The default is to fill the entire allocation. 175 176 ### fill\_on\_free[=MAX\_FILLED\_BYTES] 177 When an allocation is freed, fill it with 0xef. 178 179 If MAX\_FILLED\_BYTES is present, it will only fill up to the specified number 180 of bytes in the allocation. The default is to fill the entire allocation. 181 182 ### fill[=MAX\_FILLED\_BYTES] 183 This enables both the fill\_on\_alloc option and the fill\_on\_free option. 184 185 If MAX\_FILLED\_BYTES is present, it will only fill up to the specified number 186 of bytes in the allocation. The default is to fill the entire allocation. 187 188 ### expand\_alloc[=EXPAND\_BYTES] 189 Add an extra amount to allocate for every allocation. 190 191 If XX is present, it is the number of bytes to expand the allocation by. 192 The default is 16 bytes, the max bytes is 16384. 193 194 ### free\_track[=ALLOCATION\_COUNT] 195 When a pointer is freed, do not free the memory right away, but add it to 196 a list of freed allocations. In addition to being added to the list, the 197 entire allocation is filled with the value 0xef, and the backtrace at 198 the time of the free is recorded. The backtrace recording is completely 199 separate from the backtrace option, and happens automatically if this 200 option is enabled. By default, a maximum of 16 frames will be recorded, 201 but this value can be changed using the free\_track\_backtrace\_num\_frames 202 option. It can also be completely disabled by setting the option to zero. 203 See the full description of this option below. 204 205 When the list is full, an allocation is removed from the list and is 206 checked to make sure that none of the contents have been modified since 207 being placed on the list. When the program terminates, all of the allocations 208 left on the list are verified. 209 210 If ALLOCATION\_COUNT is present, it indicates the total number of allocations 211 in the list. The default is to record 100 freed allocations, the max 212 allocations to record is 16384. 213 214 Before P, this option adds a special header to all allocations that contains 215 the backtrace and information about the original allocation. After that, this 216 option will not add a special header. 217 218 Example error: 219 220 04-15 12:00:31.304 7412 7412 E malloc_debug: +++ ALLOCATION 0x12345678 USED AFTER FREE 221 04-15 12:00:31.305 7412 7412 E malloc_debug: allocation[20] = 0xaf (expected 0xef) 222 04-15 12:00:31.305 7412 7412 E malloc_debug: allocation[99] = 0x12 (expected 0xef) 223 04-15 12:00:31.305 7412 7412 E malloc_debug: Backtrace at time of free: 224 04-15 12:00:31.305 7412 7412 E malloc_debug: #00 pc 00029310 /system/lib/libc.so 225 04-15 12:00:31.305 7412 7412 E malloc_debug: #01 pc 00021438 /system/lib/libc.so (newlocale+160) 226 04-15 12:00:31.305 7412 7412 E malloc_debug: #02 pc 000a9e38 /system/lib/libc++.so 227 04-15 12:00:31.305 7412 7412 E malloc_debug: #03 pc 000a28a8 /system/lib/libc++.so 228 229 In addition, there is another type of error message that can occur if 230 an allocation has a special header applied, and the header is corrupted 231 before the verification occurs. This is the error message that will be found 232 in the log: 233 234 04-15 12:00:31.604 7412 7412 E malloc_debug: +++ ALLOCATION 0x12345678 HAS CORRUPTED HEADER TAG 0x1cc7dc00 AFTER FREE 235 236 ### free\_track\_backtrace\_num\_frames[=MAX\_FRAMES] 237 This option only has meaning if free\_track is set. It indicates how many 238 backtrace frames to capture when an allocation is freed. 239 240 If MAX\_FRAMES is present, it indicates the number of frames to capture. 241 If the value is set to zero, then no backtrace will be captured when the 242 allocation is freed. The default is to record 16 frames, the max number of 243 frames to to record is 256. 244 245 ### leak\_track 246 Track all live allocations. When the program terminates, all of the live 247 allocations will be dumped to the log. If the backtrace option was enabled, 248 then the log will include the backtrace of the leaked allocations. This 249 option is not useful when enabled globally because a lot of programs do not 250 free everything before the program terminates. 251 252 Before P, this option adds a special header to all allocations that contains 253 the backtrace and information about the original allocation. After that, this 254 option will not add a special header. 255 256 Example leak error found in the log: 257 258 04-15 12:35:33.304 7412 7412 E malloc_debug: +++ APP leaked block of size 100 at 0x2be3b0b0 (leak 1 of 2) 259 04-15 12:35:33.304 7412 7412 E malloc_debug: Backtrace at time of allocation: 260 04-15 12:35:33.305 7412 7412 E malloc_debug: #00 pc 00029310 /system/lib/libc.so 261 04-15 12:35:33.305 7412 7412 E malloc_debug: #01 pc 00021438 /system/lib/libc.so (newlocale+160) 262 04-15 12:35:33.305 7412 7412 E malloc_debug: #02 pc 000a9e38 /system/lib/libc++.so 263 04-15 12:35:33.305 7412 7412 E malloc_debug: #03 pc 000a28a8 /system/lib/libc++.so 264 04-15 12:35:33.305 7412 7412 E malloc_debug: +++ APP leaked block of size 24 at 0x7be32380 (leak 2 of 2) 265 04-15 12:35:33.305 7412 7412 E malloc_debug: Backtrace at time of allocation: 266 04-15 12:35:33.305 7412 7412 E malloc_debug: #00 pc 00029310 /system/lib/libc.so 267 04-15 12:35:33.305 7412 7412 E malloc_debug: #01 pc 00021438 /system/lib/libc.so (newlocale+160) 268 04-15 12:35:33.305 7412 7412 E malloc_debug: #02 pc 000a9e38 /system/lib/libc++.so 269 04-15 12:35:33.305 7412 7412 E malloc_debug: #03 pc 000a28a8 /system/lib/libc++.so 270 271 ### record\_allocs[=TOTAL\_ENTRIES] 272 Keep track of every allocation/free made on every thread and dump them 273 to a file when the signal SIGRTMAX - 18 (which is 46 on most Android devices) 274 is received. 275 276 If TOTAL\_ENTRIES is set, then it indicates the total number of 277 allocation/free records that can be retained. If the number of records 278 reaches the TOTAL\_ENTRIES value, then any further allocations/frees are 279 not recorded. The default value is 8,000,000 and the maximum value this 280 can be set to is 50,000,000. 281 282 Once the signal is received, and the current records are written to the 283 file, all current records are deleted. Any allocations/frees occuring while 284 the data is being dumped to the file are ignored. 285 286 **NOTE**: This option is not available until the O release of Android. 287 288 The allocation data is written in a human readable format. Every line begins 289 with the THREAD\_ID returned by gettid(), which is the thread that is making 290 the allocation/free. If a new thread is created, no special line is added 291 to the file. However, when a thread completes, a special entry is added to 292 the file indicating this. 293 294 The thread complete line is: 295 296 **THREAD\_ID**: thread\_done 0x0 297 298 Example: 299 300 187: thread_done 0x0 301 302 Below is how each type of allocation/free call ends up in the file dump. 303 304 pointer = malloc(size) 305 306 **THREAD\_ID**: malloc pointer size 307 308 Example: 309 310 186: malloc 0xb6038060 20 311 312 free(pointer) 313 314 **THREAD\_ID**: free pointer 315 316 Example: 317 318 186: free 0xb6038060 319 320 pointer = calloc(nmemb, size) 321 322 **THREAD\_ID**: calloc pointer nmemb size 323 324 Example: 325 326 186: calloc 0xb609f080 32 4 327 328 new\_pointer = realloc(old\_pointer, size) 329 330 **THREAD\_ID**: realloc new\_pointer old\_pointer size 331 332 Example: 333 334 186: realloc 0xb609f080 0xb603e9a0 12 335 336 pointer = memalign(alignment, size) 337 338 **THREAD\_ID**: memalign pointer alignment size 339 340 pointer = aligned\_alloc(alignment, size) 341 342 **THREAD\_ID**: memalign pointer alignment size 343 344 posix\_memalign(&pointer, alignment, size) 345 346 **THREAD\_ID**: memalign pointer alignment size 347 348 Example: 349 350 186: memalign 0x85423660 16 104 351 352 pointer = valloc(size) 353 354 **THREAD\_ID**: memalign pointer 4096 size 355 356 Example: 357 358 186: memalign 0x85423660 4096 112 359 360 pointer = pvalloc(size) 361 362 **THREAD\_ID**: memalign pointer 4096 <b>SIZE\_ROUNDED\_UP\_TO\_4096</b> 363 364 Example: 365 366 186: memalign 0x85423660 4096 8192 367 368 ### record\_allocs\_file[=FILE\_NAME] 369 This option only has meaning if record\_allocs is set. It indicates the 370 file where the recorded allocations will be found. 371 372 If FILE\_NAME is set, then it indicates where the record allocation data 373 will be placed. 374 375 **NOTE**: This option is not available until the O release of Android. 376 377 ### verify\_pointers 378 Track all live allocations to determine if a pointer is used that does not 379 exist. This option is a lightweight way to verify that all 380 free/malloc\_usable\_size/realloc calls are passed valid pointers. 381 382 Example error: 383 384 04-15 12:00:31.304 7412 7412 E malloc_debug: +++ ALLOCATION 0x12345678 UNKNOWN POINTER (free) 385 04-15 12:00:31.305 7412 7412 E malloc_debug: Backtrace at time of failure: 386 04-15 12:00:31.305 7412 7412 E malloc_debug: #00 pc 00029310 /system/lib/libc.so 387 04-15 12:00:31.305 7412 7412 E malloc_debug: #01 pc 00021438 /system/lib/libc.so (newlocale+160) 388 04-15 12:00:31.305 7412 7412 E malloc_debug: #02 pc 000a9e38 /system/lib/libc++.so 389 04-15 12:00:31.305 7412 7412 E malloc_debug: #03 pc 000a28a8 /system/lib/libc++.so 390 391 Where the name of the function varies depending on the function that called 392 with a bad pointer. Only three functions do this checking: free, 393 malloc\_usable\_size, realloc. 394 395 **NOTE**: This option is not available until the P release of Android. 396 397 ### abort\_on\_error 398 When malloc debug detects an error, abort after sending the error 399 log message. 400 401 **NOTE**: If leak\_track is enabled, no abort occurs if leaks have been 402 detected when the process is exiting. 403 404 ### verbose 405 As of Android Q, all info messages will be turned off by default. For example, 406 in Android P and older, enabling malloc debug would result in this message 407 in the log: 408 409 08-16 15:54:16.060 26947 26947 I libc : /system/bin/app_process64: malloc debug enabled 410 411 In android Q, this message will not be displayed because these info messages 412 slow down process start up. However, if you want to re-enable these messages, 413 add the verbose option. All of the "Run XXX" messages are also silenced unless 414 the verbose option is specified. This is an example of the type 415 of messages that are no longer displayed: 416 417 09-10 01:03:50.070 557 557 I malloc_debug: /system/bin/audioserver: Run: 'kill -47 557' to dump the backtrace. 418 419 Additional Errors 420 ----------------- 421 There are a few other error messages that might appear in the log. 422 423 ### Use After Free 424 04-15 12:00:31.304 7412 7412 E malloc_debug: +++ ALLOCATION 0x12345678 USED AFTER FREE (free) 425 04-15 12:00:31.305 7412 7412 E malloc_debug: Backtrace of original free: 426 04-15 12:00:31.305 7412 7412 E malloc_debug: #00 pc 00029310 /system/lib/libc.so 427 04-15 12:00:31.305 7412 7412 E malloc_debug: #01 pc 00021438 /system/lib/libc.so (newlocale+160) 428 04-15 12:00:31.305 7412 7412 E malloc_debug: #02 pc 000a9e38 /system/lib/libc++.so 429 04-15 12:00:31.305 7412 7412 E malloc_debug: #03 pc 000a28a8 /system/lib/libc++.so 430 04-15 12:00:31.305 7412 7412 E malloc_debug: Backtrace at time of failure: 431 04-15 12:00:31.305 7412 7412 E malloc_debug: #00 pc 00029310 /system/lib/libc.so 432 04-15 12:00:31.305 7412 7412 E malloc_debug: #01 pc 00021438 /system/lib/libc.so (newlocale+160) 433 04-15 12:00:31.305 7412 7412 E malloc_debug: #02 pc 000a9e38 /system/lib/libc++.so 434 04-15 12:00:31.305 7412 7412 E malloc_debug: #03 pc 000a28a8 /system/lib/libc++.so 435 436 This indicates that code is attempting to free an already freed pointer. The 437 name in parenthesis indicates that the application called the function 438 *free* with the bad pointer. 439 440 For example, this message: 441 442 04-15 12:00:31.304 7412 7412 E malloc_debug: +++ ALLOCATION 0x12345678 USED AFTER FREE (realloc) 443 444 Would indicate that the application called the *realloc* function 445 with an already freed pointer. 446 447 ### Invalid Tag 448 04-15 12:00:31.304 7412 7412 E malloc_debug: +++ ALLOCATION 0x12345678 HAS INVALID TAG 1ee7d000 (malloc_usable_size) 449 04-15 12:00:31.305 7412 7412 E malloc_debug: Backtrace at time of failure: 450 04-15 12:00:31.305 7412 7412 E malloc_debug: #00 pc 00029310 /system/lib/libc.so 451 04-15 12:00:31.305 7412 7412 E malloc_debug: #01 pc 00021438 /system/lib/libc.so (newlocale+160) 452 04-15 12:00:31.305 7412 7412 E malloc_debug: #02 pc 000a9e38 /system/lib/libc++.so 453 04-15 12:00:31.305 7412 7412 E malloc_debug: #03 pc 000a28a8 /system/lib/libc++.so 454 455 This indicates that a function (malloc\_usable\_size) was called with 456 a pointer that is either not allocated memory, or that the memory of 457 the pointer has been corrupted. 458 459 As with the other error message, the function in parenthesis is the 460 function that was called with the bad pointer. 461 462 Backtrace Heap Dump Format 463 ========================== 464 465 This section describes the format of the backtrace heap dump. This data is 466 generated by am dumpheap -n or, as of P, by the signal or on exit. 467 468 The data has this header: 469 470 Android Native Heap Dump v1.0 471 472 Total memory: XXXX 473 Allocation records: YYYY 474 Backtrace size: ZZZZ 475 476 Total memory is the total of all of the currently live allocations. 477 Allocation records is the total number of allocation records. 478 Backtrace size is the maximum number of backtrace frames that can be present. 479 480 Following this header are two different sections, the first section is the 481 allocation records, the second section is the map data. 482 483 The allocation record data has this format: 484 485 z ZYGOTE_CHILD_ALLOC sz ALLOCATION_SIZE num NUM_ALLOCATIONS bt FRAMES 486 487 ZYGOTE\_CHILD\_ALLOC is either 0 or 1. 0 means this was allocated by the 488 zygote process or in a process not spawned from the zygote. 1 means this 489 was allocated by an application after it forked off from the zygote process. 490 491 ALLOCATION\_SIZE is the size of the allocation. 492 NUM\_ALLOCATIONS is the number of allocations that have this size and have the 493 same backtrace. 494 FRAMES is a list of instruction pointers that represent the backtrace of the 495 allocation. 496 497 Example: 498 499 z 0 sz 400 num 1 bt 0000a230 0000b500 500 z 1 sz 500 num 3 bt 0000b000 0000c000 501 502 The first allocation record was created by the zygote of size 400 only one 503 with this backtrace/size and a backtrace of 0xa230, 0xb500. 504 The second allocation record was create by an application spawned from the 505 zygote of size 500, where there are three of these allocation with the same 506 backtrace/size and a backtrace of 0xb000, 0xc000. 507 508 The final section is the map data for the process: 509 510 MAPS 511 7fe9181000-7fe91a2000 rw-p 00000000 00:00 0 /system/lib/libc.so 512 . 513 . 514 . 515 END 516 517 The map data is simply the output of /proc/PID/maps. This data can be used to 518 decode the frames in the backtraces. 519 520 There are now multiple versions of the file: 521 522 Android P produces version v1.1 of the heap dump. 523 524 Android Native Heap Dump v1.1 525 526 The only difference between v1.0 and v1.1 is that the NUM\_ALLOCATIONS 527 value is always accurate in v1.1. A previous version of malloc debug set 528 NUM\_ALLOCATIONS to an incorrect value. For heap dump v1.0, the 529 NUM\_ALLOCATIONS value should be treated as always 1 no matter what is 530 actually present. 531 532 Android Q introduces v1.2 of the heap dump. The new header looks like this: 533 534 Android Native Heap Dump v1.2 535 536 Build fingerprint: 'google/taimen/taimen:8.1.0/OPM2.171026.006.C1/4769658:user/release-keys' 537 538 The new line fingerprint line is the contents of the ro.build.fingerprint 539 property. 540 541 The new version no longer 0 pads the backtrace addresses. In v1.0/v1.1: 542 543 z 0 sz 400 num 1 bt 0000a230 0000b500 544 545 While v1.2: 546 547 z 0 sz 400 num 1 bt a230 b500 548 549 In addition, when the new option backtrace\_full is used, another line will 550 be added to every backtrace line. The line will be: 551 552 bt_info {"MAP_NAME" RELATIVE_TO_MAP_PC "FUNCTION_NAME" FUNCTION_OFFSET} ... 553 554 For each backtrace pc, there will be one element in braces. 555 556 MAP\_NAME is the name of the map in which the backtrace pc exists. If there is 557 no valid map name, this will be empty. 558 RELATIVE\_TO\_MAP\_PC is the hexadecimal value of the relative pc to the map. 559 FUNCTION\_NAME the name of the function for this pc. If there is no valid 560 function name, then it will be empty. 561 FUNCTION\_OFFSET the hexadecimal offset from the beginning of the function. If 562 the FUNCTION\_NAME is empty, then this value will always be zero. 563 564 An example of this new format: 565 566 z 0 sz 400 num 1 bt a2a0 b510 567 bt_info {"/system/libc.so" 2a0 "abort" 24} {"/system/libutils.so" 510 "" 0} 568 569 In this example, the first backtrace frame has a pc of 0xa2a0 and is in the 570 map named /system/libc.so which starts at 0xa000. The relative pc is 0x2a0, 571 and it is in the function abort + 0x24. 572 The second backtrace frame has a pc of 0xb510 and is in the map named 573 /system/libutils.so which starts at 0xb000. The relative pc is 0x510 and 574 it is in an unknown function. 575 576 There is a tool to visualize this data, 577 [native\_heapdump\_viewer.py](https://android.googlesource.com/platform/development/+/master/scripts/native_heapdump_viewer.py). 578 579 Examples 580 ======== 581 582 ### For platform developers 583 584 Enable backtrace tracking of all allocation for all processes: 585 586 adb shell stop 587 adb shell setprop libc.debug.malloc.options backtrace 588 adb shell start 589 590 Enable backtrace tracking for a specific process (ls): 591 592 adb shell setprop libc.debug.malloc.options backtrace 593 adb shell setprop libc.debug.malloc.program ls 594 adb shell ls 595 596 Enable backtrace tracking for the zygote and zygote based processes: 597 598 adb shell stop 599 adb shell setprop libc.debug.malloc.program app_process 600 adb shell setprop libc.debug.malloc.options backtrace 601 adb shell start 602 603 Enable multiple options (backtrace and guard): 604 605 adb shell stop 606 adb shell setprop libc.debug.malloc.options "\"backtrace guard\"" 607 adb shell start 608 609 Note: The two levels of quoting in the adb shell command is necessary. 610 The outer layer of quoting is for the shell on the host, to ensure that the 611 inner layer of quoting is sent to the device, to make 'backtrace guard' 612 a single argument. 613 614 Enable malloc debug using an environment variable (pre-O Android release): 615 616 adb shell 617 # setprop libc.debug.malloc.env_enabled 1 618 # setprop libc.debug.malloc.options backtrace 619 # export LIBC_DEBUG_MALLOC_ENABLE=1 620 # ls 621 622 Enable malloc debug using an environment variable (Android O or later): 623 624 adb shell 625 # export LIBC_DEBUG_MALLOC_OPTIONS=backtrace 626 # ls 627 628 Any process spawned from this shell will run with malloc debug enabled 629 using the backtrace option. 630 631 adb shell stop 632 adb shell setprop libc.debug.malloc.options backtrace 633 adb shell start 634 adb shell am dumpheap -n <PID_TO_DUMP> /data/local/tmp/heap.txt 635 636 It is possible to use the backtrace\_enable\_on\_signal option as well, 637 but, obviously, it must be enabled through the signal before the file will 638 contain any data. 639 640 ### For app developers 641 642 App developers should check the NDK documentation about 643 [wrap.sh](https://developer.android.com/ndk/guides/wrap-script.html) 644 for the best way to use malloc debug in Android O or later on non-rooted 645 devices. 646 647 If you do have a rooted device, you can enable malloc debug for a specific 648 program/application (Android O or later): 649 650 adb shell setprop wrap.<APP> '"LIBC_DEBUG_MALLOC_OPTIONS=backtrace logwrapper"' 651 652 If you need to enable multiple options using this method, then you can set 653 them like so: 654 655 adb shell setprop wrap.<APP> '"LIBC_DEBUG_MALLOC_OPTIONS=backtrace\ leak_track\ fill logwrapper"' 656 657 For example, to enable malloc debug for the google search box (Android O or later): 658 659 adb shell setprop wrap.com.google.android.googlequicksearchbox '"LIBC_DEBUG_MALLOC_OPTIONS=backtrace logwrapper"' 660 adb shell am force-stop com.google.android.googlequicksearchbox 661 662 If you are setting multiple options and the app does not appear to start 663 properly, check the logcat looking for this message 664 (`adb logcat -d | grep "malloc debug"`): 665 666 08-16 15:54:16.060 26947 26947 I libc : /system/bin/app_process64: malloc debug enabled 667 668 If you do not see this message, then the wrap property was not set correctly. 669 Run: 670 671 adb shell getprop | grep wrap 672 673 And verify that any spaces are properly escaped. 674 675 NOTE: On pre-O versions of the Android OS, property names had a length limit 676 of 32. This meant that to create a wrap property with the name of the app, it 677 was necessary to truncate the name to fit. On O, property names can be 678 an order of magnitude larger, so there should be no need to truncate the name 679 at all. 680 681 To detect leaks while an app is running: 682 683 adb shell dumpsys meminfo --unreachable <PID_OF_APP> 684 685 Without also enabling malloc debug, this command will only tell 686 you whether it can detect leaked memory, not where those leaks are 687 occurring. If you enable malloc debug with the backtrace option for your 688 app before running the dumpsys command, you'll get backtraces showing 689 where the memory was allocated. 690 691 For backtraces from your app to be useful, you'll want to keep the 692 symbols in your app's shared libraries rather than stripping them. That 693 way you'll see the location of the leak directly without having to use 694 something like the <code>ndk-stack</code> tool. 695 696 ### Analyzing heap dumps 697 698 To analyze the data produced by the dumpheap command, run 699 [development/scripts/native\_heapdump\_viewer.py](https://android.googlesource.com/platform/development/+/master/scripts/native_heapdump_viewer.py) 700 701 In order for the script to properly symbolize the stacks in the file, 702 make sure the script is executed from the tree that built the image. 703 704 To collect, transfer, and analyze a dump: 705 706 adb shell am dumpheap -n <PID_TO_DUMP> /data/local/tmp/heap.txt 707 adb shell pull /data/local/tmp/heap.txt . 708 python development/scripts/native_heapdump_viewer.py --symbols /some/path/to/symbols/ heap.txt > heap_info.txt 709 710 At the moment, the script will look for symbols in the given directory, 711 using the path the .so file would have on the device. So if your .so file 712 is at `/data/app/.../lib/arm/libx.so` on the device, it will need to be at 713 `/some/path/to/symbols/data/app/.../lib/arm/libx.so` locally given the 714 command line above. That is: you need to mirror the directory structure 715 for the app in the symbols directory. 716
