Question

I have a scroll view app which runs fine on the simulator, however, when installed on the device, it gives me an EXC_BAD_ACCESS, when i attempt to scroll one page. I have ran it through Instruments with Allocations and Leaks, but nothing is leaked and no zombies are messaged… i’m just curious what could cause such a difference in simulator vs device? Any ways to debug this, since my symbolicated crash log (partial below), doesn’t seem to be very symbolicated.

Exception Type: EXC_BAD_ACCESS (SIGBUS)
Exception Codes: KERN_PROTECTION_FAILURE at 0x0000000f
Crashed Thread: 0

Thread 0 Crashed:
0 libobjc.A.dylib            0x0000286e objc_msgSend + 18
1 MyApp                       0x00004fee 0x1000 + 16366
2 UIKit                         0x000668f4 -[UIViewController view] + 104
3 MyApp                     0x00009716 0x1000 + 34582
4 MyApp                     0x0000960c 0x1000 + 34316
5 UIKit                         0x0001426c -[UIScrollView setContentOffset:] + 344

Thanks

Answer 1

Your code in the simulator could have the bug, but isn’t triggering EXC_BAD_ACCESS by just the luck that a pointer that you dereference is not in unmapped memory. A pointer could be bad, and accessed, but not detected — it’s still a bug.

You have already checked to see that no Zombies are messaged, which would have been my first suggestion.

The next thing to do is Enable Guard Malloc — and then read this

http://developer.apple.com/iphone/library/documentation/Performance/Conceptual/ManagingMemory/Articles/MallocDebug.html

You can only do this in the simulator — your goal is to use the extra-sensitive heap to make the bug throw EXC_BAD_ACCESS in the simulator.

In the article:

1. Look at how to set the variables in GDB
2. Read the “Detecting Heap Corruption” section