iOS App crashes under 3.1.3 when compiled with LLVM2 - ios

Question

I have an iOS app with the following (selected) build settings in XCode 4.0.1:
Architecture = Standard (armv6 armv7)
Base SDK = Latest iOS (iOS 4.3)
iOS Deployment Target = iOS3.1
Other linker flags = -lxml2 -weak-library /usr/lib/libSystem.B.dylib
Under Targets/Build Phases, I have libSystem.B.dylib as Optional (Link Binary With Libraries).
On a 1st gen iPod Touch, I'm getting the following results:
Debug Build, C/C++ Compiler Version = LLVM Compiler 2.0, all OK
Ad Hoc Release Build, C/C++ Compiler Version = GCC 4.2, all OK
Ad Hoc Release Build, C/C++ Compiler Version = LLVM GCC 4.2, all OK
Ad Hoc Release Build, C/C++ Compiler Version = LLVM Compiler 2.0, crash a few seconds after starting.
In case 4., the crash report looks like this:
Incident Identifier: 10B8B9C5-0FA5-4C83-AB13-4C3F59D5962D
CrashReporter Key: 29f7901a33e9b055c9034cd051902ea0c87e61f6
Process: TPE [1484]
Path: /var/mobile/Applications/4FA4C8CA-DB5D-4096-8458-C76382E68D02/TPE.app/TPE
Identifier: TPE
Version: ??? (???)
Code Type: ARM (Native)
Parent Process: launchd [1]
Date/Time: 2011-04-09 17:56:58.188 +1000
OS Version: iPhone OS 3.1.3 (7E18)
Report Version: 104
Exception Type: EXC_BAD_ACCESS (SIGBUS)
Exception Codes: KERN_PROTECTION_FAILURE at 0x00000000
Crashed Thread: 0
Thread 0 Crashed:
0 libSystem.B.dylib 0000000000 0 + 0
Thread 1:
0 libSystem.B.dylib 0x00001488 mach_msg_trap + 20
1 libSystem.B.dylib 0x00004064 mach_msg + 60
etc.
The crash happens after a number of routines in my code have executed (I can see console output confirming it).
Does anyone have any ideas what would cause this to work under GCC4.2, but crash under LLVM2?

Answer 1

It's just a wild guess, but there was a compiler bug recently in llvm2 that made our app crash the same way. It only happened in release mode with full optimization and only on older devices (probably a specific processor). We switched back to gcc and everything was fine again. Apple updated their compiler in mean time which "fixes bugs for iOS", but we didn't test it yet.

Answer 2

The same problem still occurs with XCode 4.2 (4D199) when code is generated with Apple LLVM compiler 3.0.
AdHoc App works fine on iOS5 on simulator, iPad1 and iPhone4.
Same AdHoc code crashes on iPhone 3 and iPod3 on iOS 4.2.1 (8C148).
Debug code works fine on all platforms.
When the problem occurs the console log shows the following:
SpringBoard[25] <Warning>: Received memory warning. Level=1
MobileSafari[283] <Warning>: Received memory warning. Level=1
configd[23] <Notice>: jetsam: kernel memory event (93), free: 241, active: 1109, inactive: 760, purgeable: 0, wired: 7878
configd[23] <Notice>: jetsam: kernel termination snapshot being created
com.apple.launchd[1] <Notice>: (UIKitApplication:com.apple.mobilesafari[0xc614]) Exited: Killed
com.apple.launchd[1] <Notice>: (UIKitApplication:com.myapp.test[0x47db]) Exited: Killed
SpringBoard[25] <Warning>: Application 'MyApp' exited abnormally with signal 9: Killed
Peak memory usage of the App is a couple Mb. The debug code never reaches a critical memory limit.
The problem disappears when either:
Optimization Level for AdHoc is set to None (-O0)
The compiler is changed to LLVM GCC 4.2
So far, extensive analyzes of code and memory management have not provided an indication what might be causing this. It seems like a compiler bug...