How to use MallocStackLogging on the device? - iphone

Question

I've a memory issue in an iPhone app that I'd like to debug with MallocStackLogging. The error involves the gyroscope so I have to debug on the device not the simulator.
I've set the MallocStackLogging environment variable and the iPhone properly records the mallock stack logs:
MyApp(1856) malloc: recording malloc stacks to disk using standard recorder
MyApp(1856) malloc: stack logs being written into /private/var/mobile/Applications/1FD1F8D2-5D30-4AA7-B426-C52FE20266DE/tmp/stack-logs.1856.MyApp.index
MyApp(1856) malloc: Please issue: cp /private/var/mobile/Applications/1FD1F8D2-5D30-4AA7- B426-C52FE20266DE/tmp/stack-logs.1856.MyApp.e8z3IL.link /tmp/
Now how can I work with them?
I can transfer them to the Mac using the Xcode Organizer. But what should I do with these two files?
stack-logs.1856.MyApp.index
stack-logs.1856.MyApp.e8z3IL.link
I tried moving the files in /tmp on the Mac and called:
$ malloc_history 1856 -all_events
malloc_history cannot examine process 1856 because the process does not exist.
Clearly, the malloc_history command looks for running processes on the local machine. I'm missing an option to specify the log file manually.
Is there any way to get this to work either directly working with Xcode on the (non-jailbroken) device or after transferring the logs to the Mac?

Answer 1

Here is how I debug APP with malloc stack history on idevice, it's really complicate, but I have no other way to deal with an auto release pool memory problem.
You need A jailbreak idevice with developer tools installed, then you have gdb.
To enable malloc stack loggin, you need set environment variables MallocStackLoggingNoCompact and MallocStackLogging, we need some trick to do it.
First, we need grant your app root privilege.
mv -f /User/Application/xxxxxxxxxxxxx/YOUR_APP.app /Application/YOUR_APP.app
cd /Application
chown -R root:wheel YOUR_APP.app
chmod 4755 YOUR_APP.app/YOUR_APP
Rename your program
mv YOUR_APP.app/YOUR_APP YOUR_APP.app/BACK_UP_NAME
Use a short shell scrip to start your program, so we can keep the env. Save it to YOUR_APP.app/YOUR_APP
#!/bin/bash
export MallocStackLogging=1
export MallocStackLoggingNoCompact=1
exec /Applications/YOUR_APP.app/BACK_UP_NAME
Done.
Just start you app, touching on the icon or use open command, you'll see a stack log file in /tmp
directory.
Use ps aux | grep YOUR_APP find process id, gdb -p PROCESS_ID attach to the progress, make a breakpoint, try info malloc ADDRESS, malloc history will show up.

Answer 2

In the Instruments application, which can diagnose an app running in the simulator or on a device, the Allocations instrument records memory addresses and allocation histories. You can browse by object/allocation type or specific memory address. This is likely the most straightforward way to accomplish what you want.
Running malloc_history on the device would require either jailbreaking to enable an ssh connection to the device, or running malloc_history from within your code. But I am not certain whether malloc_history exists on an iOS device. And malloc_history's help text does not mention an option for operating on log files rather than an existing process, which you likely already know.

Answer 3

I don't mean to sound flippant, but have you tried plugging the device in and running it under the debugger whilst connected ?
I do extensive debugging whilst runnning the application on the device. You do need to start the application under the debugger.