IMP methodForSelector EXC_BAD_ACCESS crash - ios

Question

I have received a couple of crash reports, and the only thing I can see in common is that they are both iPhone 5. I can't reproduce the crash on iPhone 5s or 6 so I I assumed it was a 64/32 bit issue. However the code also runs fine on an iPhone 4s running iOS 7.
The crash is happening on the last line here:
IMP imp = [self.delegate methodForSelector:aSelector];
id (*func)(id, SEL, id) = (void *)imp;
func(self.delegate, aSelector, self);
To be perfectly honest, I don't understand these 3 lines of code. I found them to overcome a compiler warning may cause a leak because its selector is unknown when using [self.delegate performSelector:aSelector withObject:self];
When I push an update using performSelector it doesn't crash.
I need to pass an argument of self along with the selector which is why I used IMP and added self as the third argument which is how I read it should be done.
The actual crash log doesn't reveal much:
Crashed: com.apple.main-thread EXC_BAD_ACCESS KERN_INVALID_ADDRESS at 0x00000100 Thread : Crashed: com.apple.main-thread
0 libobjc.A.dylib 0x30ca26b8 objc_retain + 7
1 Timeout 0x0009e2a1 __50-[BaseOperation finishedSuccessfullyWithSelector:]_block_invoke_2 (BaseOperation.m:47)
2 libdispatch.dylib 0x311e87bb
_dispatch_call_block_and_release + 10
3 libdispatch.dylib 0x311efe8b _dispatch_after_timer_callback + 66
4 libdispatch.dylib 0x311e87a7 _dispatch_client_callout + 22
5 libdispatch.dylib 0x311f9253 _dispatch_source_latch_and_call + 626
6 libdispatch.dylib 0x311ea2ed _dispatch_source_invoke + 212
7 libdispatch.dylib 0x311ebe1f _dispatch_main_queue_callback_4CF + 330
8 CoreFoundation 0x234a39d1 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 8
9 CoreFoundation 0x234a20d1 __CFRunLoopRun + 1512
10 CoreFoundation 0x233f0211 CFRunLoopRunSpecific + 476
11 CoreFoundation 0x233f0023 CFRunLoopRunInMode + 106
12 GraphicsServices 0x2a7e90a9 GSEventRunModal + 136
13 UIKit 0x269fc1d1 UIApplicationMain + 1440
14 Timeout 0x000a265b main (main.m:14)
Is there anyone that can shed some light on this?
Thanks
EDIT ----
I am now also seeing crashes on iPad 3 (iOS 8.1.2) & iPhone 5 (iOS 8.1). Yet still can't reproduce it myself, I also tried an iPod (iOS 8.1) and iPad mini retina (iOS 8.1.3). This is really bugging me (Pun intended).
EDIT 2 ----
I've added some Crashlytics logs to log self.delegate self imp & func and they all appear to be fine! So why does the very next line crash?
0 | 00:01:33:665 | $ __50-[BaseOperation finishedSuccessfullyWithSelector:]_block_invoke_2 : connectComplete:
1 | 00:01:33:665 | $ delegate: <BaseMenuViewController: 0x17e5e780>
2 | 00:01:33:666 | $ self: <ConnectOperation_Virgin: 0x1902a490>{name = '(null)'}
3 | 00:01:33:667 | $ imp: 0xaa345
4 | 00:01:33:667 | $ func: 0xaa345

Answer 1

I had the same problem, working code 6 months ago now crashes, fixed it with those changes :
//old code
IMP imp = [_target methodForSelector:_action];
id (*func)(id, SEL, id) = (void *)imp;
func(_target, _action, params);
//replaced by
void (*imp)(id, SEL, id) = (void(*)(id,SEL,id))[_target methodForSelector:_action];
if( imp ) imp(_target, _action, params);