Getting info about bad memory address in LLDB

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南笙 2021-01-30 04:37

I am trying to debug an EXC_BAD_ACCESS in my iPhone app. It is crashing on a method call and on the line of the method is EXC_BAD_ACCESS (code=1, address = xxx).

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  • 2021-01-30 05:06

    you can use command like this in lldb:

    image lookup --address 0xec509b
    

    you can find more commands at:LLDB TO GDB COMMAND MAP

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  • 2021-01-30 05:09

    This problem is very easy to solve with an informative backtrace. Unfortunately with the latest version of iOS and Xcode, a good stack track is sometimes hard to come by. Fortunately you can set an 'Exception Breakpoint' in Xcode to allow you to examine this code prior to the EXC_BAD_ACCESS exception.

    1. Open the breakpoint navigation in Xcode 4 (This looks like a rectangle with a point on the right side)
    2. Press the '+' button at the bottom left and add an 'Exception Breakpoint'. Ensure you break 'On Throw' for 'All' exceptions.

    Now you should get a full backtrace immediately prior to this exception occurring. This should allow you to at least zero in on where this exception is being thrown.

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  • 2021-01-30 05:20

    Maybe is too late but for further assistance, on LLDB:

    (lldb) p *(MyClassToPrint*)memory_address
    

    E.g.

    (lldb) p *(HomeViewController*)0x0a2bf700
    
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  • 2021-01-30 05:21

    You can see the malloc stack if you debug using instruments.

    I encountered the same problem as you and similarly wanted to know how to get the malloc history when using lldb. Sadly I didn't find a nifty command like malloc-history found in gdb. To be honest I just switched my debugger over, but I found that annoying since I felt I shouldn't have to do that.

    To find the malloc history using instruments:

    1. Profile your project
    2. Select Zombies from the list of instruments enter image description here
    3. Make your app trigger the problem
    4. At this point you should be presented with the address that was already deallocated and you can explore it. enter image description here It should be a simple matter of viewing the malloc history at this point. I blacked out portions that had class / project names specific to the work I'm doing, but I think the essence and usefulness of how to go about getting this information is present.

    A Last Word

    The problem I ran into yielded a message like:

    *** -[someClass retain]: message sent to deallocated instance 0x48081fb0 someProject(84051,0xacd902c0) malloc: recording malloc stacks to disk using standard recorder

    I was really puzzled where this retain was coming from since the code it was breaking on didn't have one (not in the getter or setter of the line it was on). It turns out that I was not calling removeObserver:forKeyPath: when a certain object was dealloc'ed. Later in execution KVO occurred do to a setter on a line and that blew up the program since KVO was trying to notify an object that was already released.

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