After upgrading xcode4.1/ios4 to xcode4.2/ios5 I am experiencing crashes while the App is loading and before it even enters main().
Guard malloc was the problem for me too. Probably because I'm using libxml2.2.7.3.dylib.
This question describes the same crash, but he was lucky enough to be turning guard malloc on, so it was obvious what caused the crash. I just got the crash after upgrading Xcode to 4.2.
I'd like to include the stack trace so that it is Googleable. I had trouble finding this page.
#0 0x00000000 in ???> ()
#1 0x99924ef3 in mig_get_reply_port ()
#2 0x9991e70c in mach_ports_lookup ()
#3 0x0141c124 in _xpc_domain_init_local ()
#4 0x01419eb1 in _libxpc_initializer ()
#5 0x8fe2a15b in __dyld__ZN16ImageLoaderMachO18doModInitFunctionsERKN11ImageLoader11LinkContextE ()
#6 0x8fe29cc0 in __dyld__ZN16ImageLoaderMachO16doInitializationERKN11ImageLoader11LinkContextE ()
#7 0x8fe27220 in __dyld__ZN11ImageLoader23recursiveInitializationERKNS_11LinkContextEjRNS_21InitializerTimingListE ()
#8 0x8fe271b6 in __dyld__ZN11ImageLoader23recursiveInitializationERKNS_11LinkContextEjRNS_21InitializerTimingListE ()
#9 0x8fe271b6 in __dyld__ZN11ImageLoader23recursiveInitializationERKNS_11LinkContextEjRNS_21InitializerTimingListE ()
#10 0x8fe271b6 in __dyld__ZN11ImageLoader23recursiveInitializationERKNS_11LinkContextEjRNS_21InitializerTimingListE ()
#11 0x8fe271b6 in __dyld__ZN11ImageLoader23recursiveInitializationERKNS_11LinkContextEjRNS_21InitializerTimingListE ()
#12 0x8fe281c0 in __dyld__ZN11ImageLoader15runInitializersERKNS_11LinkContextERNS_21InitializerTimingListE ()
#13 0x8fe1c626 in __dyld__ZN4dyld24initializeMainExecutableEv ()
#14 0x8fe20ef2 in __dyld__ZN4dyld5_mainEPK12macho_headermiPPKcS5_S5_ ()
#15 0x8fe1a2ef in __dyld__ZN13dyldbootstrap5startEPK12macho_headeriPPKclS2_ ()
#16 0x8fe1a063 in __dyld__dyld_start ()