Question

I’m trying to build my own signal and uncaught exception handler for iOS. To do this i use these two functions :

NSSetUncaughtExceptionHandler(/*handler*/); 

and

signal(/*signal const*/, /*signal handler*/);

My problem is that i can’t make it work with EXC_BAD_ACCESS signal. Is there some signal constant (like SIGABRT, SIGBUS) to catch the EXC_BAD_ACCESS? If no, how can i handle it? Some crash analytics tools (lika PLCrashReporter, Crashlytics etc.) can trace it…

Answer 1

EXC_BAD_ACCESS doesn’t generate an exception so you first function doesn’t work with the case. It generates a signal SIGSEGV or SIGBUS.

Please refer to Handling unhandled exceptions and signals by Cocoa with Love.

Update

I just checked the source code of LLDB. It might be TARGET_EXC_BAD_ACCESS = 0x91.

In RNBRemote.h:

/* We translate the /usr/include/mach/exception_types.h exception types
   (e.g. EXC_BAD_ACCESS) to the fake BSD signal numbers that gdb uses
   in include/gdb/signals.h (e.g. TARGET_EXC_BAD_ACCESS).  These hard
   coded values for TARGET_EXC_BAD_ACCESS et al must match the gdb
   values in its include/gdb/signals.h.  */

#define TARGET_EXC_BAD_ACCESS      0x91
#define TARGET_EXC_BAD_INSTRUCTION 0x92
#define TARGET_EXC_ARITHMETIC      0x93
#define TARGET_EXC_EMULATION       0x94
#define TARGET_EXC_SOFTWARE        0x95
#define TARGET_EXC_BREAKPOINT      0x96

and in RNBRemote.cpp:

// Translate any mach exceptions to gdb versions, unless they are
// common exceptions like a breakpoint or a soft signal.
switch (tid_stop_info.details.exception.type)
{
    default:                    signum = 0; break;
    case EXC_BREAKPOINT:        signum = SIGTRAP; break;
    case EXC_BAD_ACCESS:        signum = TARGET_EXC_BAD_ACCESS; break;
    case EXC_BAD_INSTRUCTION:   signum = TARGET_EXC_BAD_INSTRUCTION; break;
    case EXC_ARITHMETIC:        signum = TARGET_EXC_ARITHMETIC; break;
    case EXC_EMULATION:         signum = TARGET_EXC_EMULATION; break;
    case EXC_SOFTWARE:
        if (tid_stop_info.details.exception.data_count == 2 &&
            tid_stop_info.details.exception.data[0] == EXC_SOFT_SIGNAL)
            signum = tid_stop_info.details.exception.data[1];
        else
            signum = TARGET_EXC_SOFTWARE;
        break;
}