Cannot debug double-free crash

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I'm getting a crash from freeing an autorelease variable. I believe it is an over-release because the crash comes when the autorelease pool is released on a secondary thread. The following warning is sent (NSZombieEnabled = YES).

*** -[NSConcreteData release]: message sent to deallocated instance 0x85db5f0

Using breakpoints and NSZombieEnable I have found the object type and address but can't convert that to a symbol name.The crash is (likely) inside of a static library which I compiled from source and enabled debugging symbol names.

I have not been able to use atos() to find the symbol name for the memory address of the object. Our code base is too large to simply look at every line. Is there another way to find out which object is being released too many time?

Thanks.