Why does this objective-c exception backtrace show only the last two calls? - objective-c

Question

Using Xcode (4.3.3 and llvm), I set a breakpoint on all exceptions but often when the breakpoint is hit, the stack looks like this:
(lldb) bt
* thread #1: tid = 0x1c03, 0x31a891c4 libobjc.A.dylib`objc_exception_throw, stop reason = breakpoint 1.1
frame #0: 0x31a891c4 libobjc.A.dylib`objc_exception_throw
frame #1: 0x33a677b8 CoreFoundation`+[NSException raise:format:arguments:] + 100
There's no information about the caller of NSException raise:format:arguments:, the stack just stops there.
Something must have called raise so what happened to the stack? What should I look for to help me debug such issues (e.g. does this indicate some specific type of stack corruption or something else)?
Update: here's the code with the garbage.
The problem was that I accidentally wrote %s when I meant %#. Might have been a bit of a stretch to call that a properly-allocated string but I could "po imageName" in the llvm console, it just had some garbage at the end.
NSString *imageName = [NSString stringWithFormat:#"award_%s", award];
UIImage *image = [UIImage imageNamed:imageName];
[_awardIconMapping setObject:image forKey:award];
There was no thread #0 by the time the exception was hit. Using #try/#catch, I get a sensible exception from the last line (sorry, I thought it was the image= line before):
2012-07-06 10:43:36.184 CallVille[834:707] ****** Hit exception ********
-[__NSCFDictionary setObject:forKey:]: attempt to insert nil value (key: wiseGuy)

Answer 1

I use this function to print the stack traces from a NSException:
#include <execinfo.h>
#include <stdio.h>
#include <stdlib.h>
+ (void) printStackTrace: (NSException*) e
{
NSArray * addresses = [e callStackReturnAddresses];
if( [addresses count])
{
void * backtrace_frames[[addresses count]];
int i = 0;
for (NSNumber * address in addresses)
{
backtrace_frames[i] = (void *)[address unsignedLongValue];
i++;
}
char **frameStrings = backtrace_symbols(&backtrace_frames[0], [addresses count]);
if(frameStrings != NULL)
{
int x;
for(x = 0; x < [addresses count]; x++)
{
NSString *frame_description = [NSString stringWithUTF8String:frameStrings[ x]];
NSLog( #"------- %#", frame_description);
}
free( frameStrings);
frameStrings = nil;
}
}
}