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      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 <pre>
     11 <b>
     12 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);
     13 </b>
     14 </pre>
     15 
     16 <i>info</i> is set to a buffer allocated by the call that contains all of
     17 the allocation information.
     18 <i>overall\_size</i> is set to the total size of the buffer returned. If this
     19 <i>info\_size</i>
     20 value is zero, then there are no allocation being tracked.
     21 <i>total\_memory</i> is set to the sum of all allocation sizes that are live at
     22 the point of the function call. This does not include the memory allocated
     23 by the malloc debug library itself.
     24 <i>backtrace\_size</i> is set to the maximum number of backtrace entries
     25 that are present for each allocation.
     26 
     27 In order to free the buffer allocated by the function, call:
     28 
     29 <pre>
     30 <b>
     31 extern "C" void free_malloc_leak_info(uint8_t* info);
     32 </b>
     33 </pre>
     34 
     35 ### Format of info Buffer
     36 <pre>
     37 size_t size_of_original_allocation
     38 size_t num_backtrace_frames
     39 uintptr_t pc1
     40 uintptr_t pc2
     41 uintptr_t pc3
     42 .
     43 .
     44 .
     45 </pre>
     46 
     47 The number of <i>uintptr\_t</i> values is determined by the value
     48 <i>backtrace\_size</i> as returned by the original call to
     49 <i>get\_malloc\_leak\_info</i>. This value is not variable, it is the same
     50 for all the returned data. The value
     51 <i>num\_backtrace\_frames</i> contains the real number of frames found. The
     52 extra frames are set to zero. Each <i>uintptr\_t</i> is a pc of the callstack.
     53 The calls from within the malloc debug library are automatically removed.
     54 
     55 For 32 bit systems, <i>size\_t</i> and <i>uintptr\_t</i> are both 4 byte values.
     56 
     57 For 64 bit systems, <i>size\_t</i> and <i>uintptr\_t</i> are both 8 byte values.
     58 
     59 The total number of these structures returned in <i>info</i> is
     60 <i>overall\_size</i> divided by <i>info\_size</i>.
     61 
     62 Note, the size value in each allocation data structure will have bit 31 set
     63 if this allocation was created by the Zygote process. This helps to distinguish
     64 between native allocations created by the application.
     65