iPhone application is crashing and not leaving behind a .crash log file

Question

Hi folks,

I'm working on catching a seriously insidious bug that's happening in my code. The problem is, the bug is completely random and can happen either 9 minutes into the application's runtime or 30 minutes. I've gone ahead and added the fabulous PLCrashReporter to my project (http://code.google.com/p/plcrashreporter) and that works fine for trivial bugs. Also, when I'm in doubt, I will navigate to the crash logs found in ~/Library/Logs/CrashReporter/MobileDevice/ and run symbolicatecrash on the crash log. This + GDB will eventually catch any bug, except for the one I'm facing now.

Apparently the nature of this bug is preventing even Apple's crash logs to be properly written to storage. This shows when I sync my iPhone or iPod Touch with iTunes and run symbolicatecrash on my app:

sf$ symbolicatecrash foo.crash 
No crash report version in foo.crash at /usr/local/bin/symbolicatecrash line 741.

It might be that my application is not leaving a crash report at all, and exiting due to memory issues. I do indeed see the applicationWillTerminate: executing my NSLog statement before exiting, in my App Delegate. However, after running the application through ObjectAlloc, my application never reaches > 2.08MB of usage. Although if I'm reading the results proper, I did allocate over 28MB of memory throughout the entire duration of my test run.

Thanks again for everything.

Answer 1

A couple of suggestions:

1. Make sure that you're not actually calling exit(), returning from main(), or otherwise cleanly exiting anywhere in your code. If your application is just quitting, and not crashing, that obviously won't leave a log.

2. I think that running the system very rapidly out of memory can sometimes cause your application to crash without leaving a crash log. Run it under Instruments and see what the memory usage over time looks like.

3. If you have a set of steps that "often" reproduces the problem, try running it under the debugger and poking at it until it does crash. That might be a half-hour well-spent.

Having eliminated the obvious/easy, it's on to the more-obscure. Chances are that you're corrupting your heap or stack somewhere along the way, via a buffer overrun, re-using an invalid pointer, etc, etc. Here are some things to try:

1. Try running with NSZombieEnabled=YES in the environment variables. This will help you find re-use of freed objects. It does have an enormous impact on memory usage though, so it may not be applicable for everyone. Here's an Apple article dealing with NSZombie (among other things).

2. When running in the iPhone Simulator, use the "Simulate Memory Warning" item in the Hardware menu to force a low-memory condition - this can flush out bugs in that code, which otherwise runs at unpredictable times.

3. Last but not least, do a search through your code for everywhere that you use low-level C memory manipulation functions - malloc, calloc, realloc, memcpy, strcpy,strncpy, etc - and make absolutely sure that the buffer sizes are appropriate.