NAME

malloc_history — Show the malloc and anonymous VM allocations that the process has performed

SYNOPSIS

DESCRIPTION

malloc_history inspects a given process and lists the malloc and anonymous VM allocations performed by it. Anonymous VM allocations are from calls such as mach_vm_allocate that allocate raw Virtual Memory that is not backed by a file. Allocations of the VM regions underlying the malloc heaps are ignored. malloc_history relies on information provided by the standard malloc library when malloc stack logging has been enabled for the target process. See below for further information.

The target process may be specified by pid or by full or partial name, or it can be the path of a memory graph file generated by leaks or the Xcode Memory Graph Debugger.

If the -highWaterMark option is passed, malloc_history first scans through the all malloc stack log records to calculate the "high water mark" of allocated memory -- i.e., the highest amount of allocated memory used at any one time by the target process. It then shows information about the malloc allocations and anonymous VM regions that were live at that time, rather than currently alive in the target program.

The -highWaterMark option requires full mode of MallocStackLogging, in either a live process or a memory graph file recorded with -fullStackHistory.

By specifying one or more addresses, malloc_history lists all allocations and deallocations of any malloc blocks or VM regions that started at or contained those addresses. For each allocation, a stack trace describing who called malloc or free, or mach_vm_allocate, mmap, or mach_vm_deallocate is listed. If you do only wish to see events for malloc blocks and VM regions that started at the specified address, you can grep the output for that address. If -highWaterMark is passed, it only shows allocations and deallocations up to the high water mark.

Alternatively, the -allBySize and -allByCount options list all allocations that are currently live in the target process, or were live at the high water mark. Frequent allocations from the same point in the program (that is, the same call stack) are grouped together, and output presented either from largest allocations to smallest, or most allocations to least. If you also specify one or more addresses, this output is filtered to only show information for malloc blocks containing those addresses.

The -allEvents option lists all allocation and free events, for all addresses, up to the current time or to the high water mark. This output can be voluminous. If the -showContent option is passed, live allocations will have additional details as described for that option below.

The -callTree option generates a call tree of the backtraces of malloc calls and anonymous VM regions for live allocations in the target process, or for allocations that were live at the high water mark. The call tree can be filtered to backtraces of specific allocations or classes, by passing one or more addresses or a <classes-pattern>.

The <classes-pattern> regular expression is interpreted as an extended (modern) regular expression as described by the re_format(7) manual page. "malloc" or "non-object" can be used to refer to blocks that are not of any specific type. Examples of valid classes-patterns include:

The <classes-pattern> pattern can be followed by an optional allocation size specifier, which can be one of the following forms. The square brackets are required. The size can include a 'k' suffix for kilobytes, or an 'm' suffix for megabytes:

Examples of <classes-pattern> with size specifications include:

The call tree format is similar to the output from sample(1). The resulting call tree can be filtered or pruned with the filtercalltree(1) tool for further analysis. Additional options for the -callTree mode include:

All modes require the standard malloc library's debugging facility to be turned on. To do this, set either the MallocStackLogging or MallocStackLoggingNoCompact environment variable to 1 in the shell that will run the program. If MallocStackLogging is used, then when recording events, if an allocation event for an address is immediately followed by a free event for the same address, both events are removed from the event log. If MallocStackLoggingNoCompact is used, then all such immediate allocation/free pairs are kept in the event log, which can be useful when examining all events for a specific address, or when using the -allEvents option.

If both MallocStackLogging and MallocStackLoggingNoCompact are set, then MallocStackLogging takes precedence and MallocStackLoggingNoCompact is ignored.

malloc_history is particularly useful for tracking down memory smashers. Run the program to be inspected with MallocStackLogging or MallocStackLoggingNoCompact defined. Also set the environment variable MallocScribble; this causes the malloc library to overwrite freed memory with a well-known value (0x55), and occasionally checks freed malloc blocks to make sure the memory has not been overwritten since it was cleared. When malloc detects the memory has been written, it will print out a warning that the buffer was modified after being freed. You can then use malloc_history to find who allocated and freed memory at that address, and thus deduce what parts of the code might still have a pointer to the freed structure.

EXAMPLE

To see backtraces of allocations by class type or malloc size, run this command:

% malloc_history <process> -callTree -invert -showContent

SEE ALSO

malloc(3), heap(1), leaks(1), stringdups(1), vmmap(1), filtercalltree(1), DevToolsSecurity(1)

The Xcode developer tools also include Instruments, a graphical application that can give information similar to that provided by malloc_history. The Allocations instrument graphically displays dynamic, real-time information about the object and memory use in an application, including backtraces of where the allocations occurred.

CAVEATS

All memory sizes are given in binary-prefixed units. For example, "1K" refers to 1024 bytes.