65 lines
2.3 KiB
Markdown
65 lines
2.3 KiB
Markdown
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Native Memory Tracking using libc Callbacks
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-------------------------------------------
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Malloc debug can be used to get information on all of the live allocations
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in a process. The libc library in Android exports two calls that can be
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used to gather this data from a process. This tracking can be enabled using
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either the backtrace option or the backtrace\_enabled\_on\_signal option.
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The function to gather the data:
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<pre>
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<b>
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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);
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</b>
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</pre>
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<i>info</i> is set to a buffer allocated by the call that contains all of
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the allocation information.
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<i>overall\_size</i> is set to the total size of the buffer returned. If this
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<i>info\_size</i>
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value is zero, then there are no allocation being tracked.
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<i>total\_memory</i> is set to the sum of all allocation sizes that are live at
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the point of the function call. This does not include the memory allocated
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by the malloc debug library itself.
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<i>backtrace\_size</i> is set to the maximum number of backtrace entries
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that are present for each allocation.
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In order to free the buffer allocated by the function, call:
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<pre>
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<b>
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extern "C" void free_malloc_leak_info(uint8_t* info);
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</b>
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</pre>
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### Format of info Buffer
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<pre>
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size_t size_of_original_allocation
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size_t num_backtrace_frames
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uintptr_t pc1
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uintptr_t pc2
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uintptr_t pc3
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.
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.
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.
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</pre>
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The number of <i>uintptr\_t</i> values is determined by the value
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<i>backtrace\_size</i> as returned by the original call to
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<i>get\_malloc\_leak\_info</i>. This value is not variable, it is the same
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for all the returned data. The value
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<i>num\_backtrace\_frames</i> contains the real number of frames found. The
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extra frames are set to zero. Each <i>uintptr\_t</i> is a pc of the callstack.
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The calls from within the malloc debug library are automatically removed.
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For 32 bit systems, <i>size\_t</i> and <i>uintptr\_t</i> are both 4 byte values.
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For 64 bit systems, <i>size\_t</i> and <i>uintptr\_t</i> are both 8 byte values.
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The total number of these structures returned in <i>info</i> is
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<i>overall\_size</i> divided by <i>info\_size</i>.
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Note, the size value in each allocation data structure will have bit 31 set
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if this allocation was created by the Zygote process. This helps to distinguish
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between native allocations created by the application.
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