Crash Reporter for iPhone Applications (Part 2)

In part one I describe how to set up an Exception Handler, Uli discovered as first one that this handles not all cases. The missing part is a signal handler to get information of SIGSEGV, SIGBUS, … signals.

I thought the hard part of this is getting the backtrace inside a signal handler. I already found code for this, but I couldn’t use it because it was GPL. I tried the easy way, offering the author money to release it under public domain, oh boy this was a waste of time. But now that I found my own solution for this I’m happy that I didn’t spend money on this. (1 line versus 20 lines of code)

Let’s start with setting up a signal handler, the good old man page helps.

/* GeSHi (C) 2004 – 2007 Nigel McNie (http://qbnz.com/highlighter) */
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1. int main(int argc, char *argv[]) {
2.         struct sigaction mySigAction;
3.         mySigAction.sa_sigaction = mysighandler;
4.         mySigAction.sa_flags = SA_SIGINFO;
5.         sigemptyset(&mySigAction.sa_mask);
6.         sigaction(SIGQUIT, &mySigAction, NULL);
7.         sigaction(SIGILL, &mySigAction, NULL);
8.         sigaction(SIGTRAP, &mySigAction, NULL);
9.         sigaction(SIGABRT, &mySigAction, NULL);
10.         sigaction(SIGEMT, &mySigAction, NULL);
11.         sigaction(SIGFPE, &mySigAction, NULL);
12.         sigaction(SIGBUS, &mySigAction, NULL);
13.         sigaction(SIGSEGV, &mySigAction, NULL);
14.         sigaction(SIGSYS, &mySigAction, NULL);
15.         sigaction(SIGPIPE, &mySigAction, NULL);
16.         sigaction(SIGALRM, &mySigAction, NULL);
17.         sigaction(SIGXCPU, &mySigAction, NULL);
18.         sigaction(SIGXFSZ, &mySigAction, NULL);
19.        
20.         NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
21.         int retVal = UIApplicationMain(argc, argv, nil, nil);
22.         [pool release];
23.         return retVal;
24. }

And here the line of code I was searching for over two days: backtrace(3). You don’t find this little bastard if you search in Xcode Help with iPhone OS Library selected (there goes my two days)

1. void mysighandler(int sig, siginfo_t *info, void *context) {
2.         void *backtraceFrames[128];
3.         int frameCount = backtrace(backtraceFrames, 128);
4.  
5.         // report the error
6. }

Like in the Exception Handler you now just use backtrace_symbols(3). (Example)

Good luck with working down the crash reports you will get now

Crash Reporter for iPhone Applications (Part 1)
Crash Reporter for iPhone Applications (Part 2)