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59 lines
2.5 KiB
59 lines
2.5 KiB
4 months ago
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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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`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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*info* is set to a buffer allocated by the call that contains all of
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the allocation information.
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*overall\_size* is set to the total size of the buffer returned. If this
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*info\_size*
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value is zero, then there are no allocation being tracked.
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*total\_memory* 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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*backtrace\_size* 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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`extern "C" void free_malloc_leak_info(uint8_t* info);`
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### Format of info Buffer
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size_t size_of_original_allocation
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size_t num_allocations
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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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The number of *uintptr\_t* values is determined by the value
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*backtrace\_size* as returned by the original call to
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*get\_malloc\_leak\_info*. This value is not variable, it is the same
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for all the returned data. The value
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*num\_allocations* contains the total number of allocations with the same
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backtrace and size as this allocation. On Android Nougat, this value was
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incorrectly set to the number of frames in the backtrace.
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Each *uintptr\_t* is a pc of the callstack. If the total number
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of backtrace entries is less than *backtrace\_size*, the rest of the
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entries are zero.
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The calls from within the malloc debug library are automatically removed.
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For 32 bit systems, *size\_t* and *uintptr\_t* are both 4 byte values.
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For 64 bit systems, *size\_t* and *uintptr\_t* are both 8 byte values.
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The total number of these structures returned in *info* is
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*overall\_size* divided by *info\_size*.
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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 in a process forked from the Zygote process.
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This helps to distinguish between native allocations created by the application.
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