1 Native Memory Tracking using libc Callbacks 2 ------------------------------------------- 3 Malloc debug can be used to get information on all of the live allocations 4 in a process. The libc library in Android exports two calls that can be 5 used to gather this data from a process. This tracking can be enabled using 6 either the backtrace option or the backtrace\_enabled\_on\_signal option. 7 8 The function to gather the data: 9 10 `extern "C" void get_malloc_leak_info(uint8_t** info, size_t* overall_size, size_t* info_size, size_t* total_memory, size_t* backtrace_size);` 11 12 *info* is set to a buffer allocated by the call that contains all of 13 the allocation information. 14 *overall\_size* is set to the total size of the buffer returned. If this 15 *info\_size* 16 value is zero, then there are no allocation being tracked. 17 *total\_memory* is set to the sum of all allocation sizes that are live at 18 the point of the function call. This does not include the memory allocated 19 by the malloc debug library itself. 20 *backtrace\_size* is set to the maximum number of backtrace entries 21 that are present for each allocation. 22 23 In order to free the buffer allocated by the function, call: 24 25 `extern "C" void free_malloc_leak_info(uint8_t* info);` 26 27 ### Format of info Buffer 28 size_t size_of_original_allocation 29 size_t num_allocations 30 uintptr_t pc1 31 uintptr_t pc2 32 uintptr_t pc3 33 . 34 . 35 . 36 37 The number of *uintptr\_t* values is determined by the value 38 *backtrace\_size* as returned by the original call to 39 *get\_malloc\_leak\_info*. This value is not variable, it is the same 40 for all the returned data. The value 41 *num\_allocations* contains the total number of allocations with the same 42 backtrace and size as this allocation. On Android Nougat, this value was 43 incorrectly set to the number of frames in the backtrace. 44 Each *uintptr\_t* is a pc of the callstack. If the total number 45 of backtrace entries is less than *backtrace\_size*, the rest of the 46 entries are zero. 47 The calls from within the malloc debug library are automatically removed. 48 49 For 32 bit systems, *size\_t* and *uintptr\_t* are both 4 byte values. 50 51 For 64 bit systems, *size\_t* and *uintptr\_t* are both 8 byte values. 52 53 The total number of these structures returned in *info* is 54 *overall\_size* divided by *info\_size*. 55 56 Note, the size value in each allocation data structure will have bit 31 set 57 if this allocation was created in a process forked from the Zygote process. 58 This helps to distinguish between native allocations created by the application. 59
