I'm using CoreData in my app. Now add a new entry and try to save it. I don't know why but it fails with Thread 1: signal SIGABRT
This is my saving part:
var error: NSError? = nil
if !context.save(&error) {
abort()
}
It crashes in this line of code:
abort()
Does someone know why this happens and hoc I can solve it? I also use iCloud Sync if this could be a reason. Thanks a lot for your help!
Your code behaves exactly as intended. Google for "Unix abort".
NAME
abort - generate an abnormal process abort
SYNOPSIS
include
void abort(void);
DESCRIPTION
The abort() function causes abnormal process termination to occur, unless the signal SIGABRT is being caught and the signal handler does not return. The abnormal termination processing includes at least the effect of fclose() on all open streams, and message catalogue descriptors, and the default actions defined for SIGABRT. The SIGABRT signal is sent to the calling process as if by means of raise() with the argument SIGABRT.
The status made available to wait() or waitpid() by abort() will be that of a process terminated by the SIGABRT signal. The abort() function will override blocking or ignoring the SIGABRT signal.
RETURN VALUE
The abort() function does not return.
ERRORS
No errors are defined.
EXAMPLES
None.
APPLICATION USAGE
Catching the signal is intended to provide the application writer with a portable means to abort processing, free from possible interference from any implementation-provided library functions. If SIGABRT is neither caught nor ignored, and the current directory is writable, a core dump may be produced.
FUTURE DIRECTIONS
None.
SEE ALSO
exit(), kill(), raise(), signal(),
DERIVATION
Derived from Issue 1 of the SVID.
Related
My code crashed, and the following line gets highlighted in red. But some crash handle function should continue. How can i debug this crash handle function:
NSSetUncaughtExceptionHandler(&HandleException);
The error that you're generating doesn't result in an Objective-C exception, so exception handlers aren't going to be invoked for it.
If you're trying to test exception handling, you should replace your method code with a throw. If you're trying to test for handling of that specific code, you should create a signal handler for the error that's cut off by your screen shot. (SIGABRT, SIGSEGV, ...?)
I'm new to lldb and trying to diagnose an error by using po [$eax class]
The error shown in the UI is:
Thread 1: EXC_BREAKPOINT (code=EXC_i386_BPT, subcode=0x0)
Here is the lldb console including what I entered and what was returned:
(lldb) po [$eax class]
error: Execution was interrupted, reason: EXC_BAD_ACCESS (code=1, address=0xb06b9940).
The process has been returned to the state before expression evaluation.
The global breakpoint state toggle is off.
You app is getting stopped because the code you are running threw an uncaught Mach exception. Mach exceptions are the equivalent of BSD Signals for the Mach kernel - which makes up the lowest levels of the macOS operating system.
In this case, the particular Mach exception is EXC_BREAKPOINT. EXC_BREAKPOINT is a common source of confusion... Because it has the word "breakpoint" in the name people think that it is a debugger breakpoint. That's not entirely wrong, but the exception is used more generally than that.
EXC_BREAKPOINT is in fact the exception that the lower layers of Mach reports when it executes a certain instruction (a trap instruction). That trap instruction is used by lldb to implement breakpoints, but it is also used as an alternative to assert in various bits of system software. For instance, swift uses this error if you access past the end of an array. It is a way to stop your program right at the point of the error. If you are running outside the debugger, this will lead to a crash. But if you are running in the debugger, then control will be returned to the debugger with this EXC_BREAKPOINT stop reason.
To avoid confusion, lldb will never show you EXC_BREAKPOINT as the stop reason if the trap was one that lldb inserted in the program you are debugging to implement a debugger breakpoint. It will always say breakpoint n.n instead.
So if you see a thread stopped with EXC_BREAKPOINT as its stop reason, that means you've hit some kind of fatal error, usually in some system library used by your program. A backtrace at this point will show you what component is raising that error.
Anyway, then having hit that error, you tried to figure out the class of the value in the eax register by calling the class method on it by running po [$eax class]. Calling that method (which will cause code to get run in the program you are debugging) lead to a crash. That's what the "error" message you cite was telling you.
That's almost surely because $eax doesn't point to a valid ObjC object, so you're just calling a method on some random value, and that's crashing.
Note, if you are debugging a 64 bit program, then $eax is actually the lower 32 bits of the real argument passing register - $rax. The bottom 32 bits of a 64 bit pointer is unlikely to be a valid pointer value, so it is not at all surprising that calling class on it led to a crash.
If you were trying to call class on the first passed argument (self in ObjC methods) on 64 bit Intel, you really wanted to do:
(lldb) po [$rax class]
Note, that was also unlikely to work, since $rax only holds self at the start of the function. Then it gets used as a scratch register. So if you are any ways into the function (which the fact that your code fatally failed some test makes seem likely) $rax would be unlikely to still hold self.
Note also, if this is a 32 bit program, then $eax is not in fact used for argument passing - 32 bit Intel code passes arguments on the stack, not in registers.
Anyway, the first thing to do to figure out what went wrong was to print the backtrace when you get this exception, and see what code was getting run at the time this error occurred.
Clean project and restart Xcode worked for me.
I'm adding my solution, as I've struggled with the same problem and I didn't find this solution anywhere.
In my case I had to run Product -> Clean Build Folder (Clean + Option key) and rebuild my project. Breakpoints and lldb commands started to work properly.
In my first few dummy apps(for practice while learning) I have come across a lot of EXC_BAD_ACCESS, that somehow taught me Bad-Access is : You are touching/Accessing a object that you shouldn't because either it is not allocated yet or deallocated or simply you are not authorized to access it.
Look at this sample code that has bad-access issue because I am trying to modify a const :
-(void)myStartMethod{
NSString *str = #"testing";
const char *charStr = [str UTF8String];
charStr[4] = '\0'; // bad access on this line.
NSLog(#"%s",charStr);
}
While Segmentation fault says : Segmentation fault is a specific kind of error caused by accessing memory that “does not belong to you.” It’s a helper mechanism that keeps you from corrupting the memory and introducing hard-to-debug memory bugs. Whenever you get a segfault you know you are doing something wrong with memory (more description here.
I wanna know two things.
One, Am I right about objective-C's EXC_BAD_ACCESS ? Do I get it right ?
Second, Are EXC_BAD_ACCESS and Segmentation fault same things and Apple has just improvised its name?
No, EXC_BAD_ACCESS is not the same as SIGSEGV.
EXC_BAD_ACCESS is a Mach exception (A combination of Mach and xnu compose the Mac OS X kernel), while SIGSEGV is a POSIX signal. When crashes occur with cause given as EXC_BAD_ACCESS, often the signal is reported in parentheses immediately after: For instance, EXC_BAD_ACCESS(SIGSEGV). However, there is one other POSIX signal that can be seen in conjunction with EXC_BAD_ACCESS: It is SIGBUS, reported as EXC_BAD_ACCESS(SIGBUS).
SIGSEGV is most often seen when reading from/writing to an address that is not at all mapped in the memory map, like the NULL pointer, or attempting to write to a read-only memory location (as in your example above). SIGBUS on the other hand can be seen even for addresses the process has legitimate access to. For instance, SIGBUS can smite a process that dares to load/store from/to an unaligned memory address with instructions that assume an aligned address, or a process that attempts to write to a page for which it has not the privilege level to do so.
Thus EXC_BAD_ACCESS can best be understood as the set of both SIGSEGV and SIGBUS, and refers to all ways of incorrectly accessing memory (whether because said memory does not exist, or does exist but is misaligned, privileged or whatnot), hence its name: exception – bad access.
To feast your eyes, here is the code, within the xnu-1504.15.3 (Mac OS X 10.6.8 build 10K459) kernel source code, file bsd/uxkern/ux_exception.c beginning at line 429, that translates EXC_BAD_ACCESS to either SIGSEGV or SIGBUS.
/*
* ux_exception translates a mach exception, code and subcode to
* a signal and u.u_code. Calls machine_exception (machine dependent)
* to attempt translation first.
*/
static
void ux_exception(
int exception,
mach_exception_code_t code,
mach_exception_subcode_t subcode,
int *ux_signal,
mach_exception_code_t *ux_code)
{
/*
* Try machine-dependent translation first.
*/
if (machine_exception(exception, code, subcode, ux_signal, ux_code))
return;
switch(exception) {
case EXC_BAD_ACCESS:
if (code == KERN_INVALID_ADDRESS)
*ux_signal = SIGSEGV;
else
*ux_signal = SIGBUS;
break;
case EXC_BAD_INSTRUCTION:
*ux_signal = SIGILL;
break;
...
Edit in relation to another of your questions
Please note that exception here does not refer to an exception at the level of the language, of the type one may catch with syntactical sugar like try{} catch{} blocks. Exception here refers to the actions of a CPU on encountering certain types of mistakes in your program (they may or may not be be fatal), like a null-pointer dereference, that require outside intervention.
When this happens, the CPU is said to raise what is commonly called either an exception or an interrupt. This means that the CPU saves what it was doing (the context) and deals with the exceptional situation.
To deal with such an exceptional situation, the CPU does not start executing any "exception-handling" code (catch-blocks or suchlike) in your application. It first gives the OS control, by starting to execute a kernel-provided piece of code called an interrupt service routine. This is a piece of code that figures out what happened to which process, and what to do about it. The OS thus has an opportunity to judge the situation, and take the action it wants.
The action it does for an invalid memory access (such as a null pointer dereference) is to signal the guilty process with EXC_BAD_ACCESS(SIGSEGV). The action it does for a misaligned memory access is to signal the guilty process with EXC_BAD_ACCESS(SIGBUS). There are many other exceptional situations and corresponding actions, not all of which involve signals.
We're now back in the context of your program. If your program receives the SIGSEGV or SIGBUS signals, it will invoke the signal handler that was installed for that signal, or the default one if none was. It is rare for people to install custom handlers for SIGSEGV and SIGBUS and the default handlers shut down your program, so what you usually get is your program being shut down.
This sort of exceptions is therefore completely unlike the sort one throws in try{}-blocks and catch{}es. Those exceptions are handled purely within the application, without involving the OS at all. Here what happens is that a throw statement is simply a glorified jump to the inner-most catch block that handles that exception. As the exception bubbles through the stack, it unwinds the stack behind it, running destructors and suchlike as needed.
Basically yes, indeed an EXC_BAD_ACCESS is usually paired with a SIGSEGV which is a signal that warns about the segmentation failure.
A segmentation failure is risen whenever you are working with a pointer that points to invalid data (maybe not belonging to the process, maybe read-only, maybe an invalid address in general).
Don't think about the segmentation fault in terms of "accessing an object", you are accessing a memory location, so an address. That address must be considered coherent by the OS memory protection system.
Not all errors which are related to accessing invalid data can be tracked by the memory manager, think about a pointer to a stack allocated variable, which is considered valid although its content is not valid anymore upon restoring the stack frame.
I am reproducibly getting an exception on this line
UIImage * image = [UIImage imageWithContentsOfFile:path]; // Always main thread
The exception is not fatal, if breakpoints are disabled the app continues normally. I presume the exception is caught in Apple's code.
The message logged is:
< Error >: ImageIO: CreateMetadataFromXMPBufferInternal
Threw error #11 (Acquire pthread write lock failed)
Stack-trace:
The code is accessing a file path that the ASI Networking library owns.
There is another background ASI thread thats checking for existence of the the URL string but I don't believe its actually writing anything to disk.
The code is iterates over 8 successfully, then fails on the 9th.
Anyone seen this issue before or know whats causing it?
I'm trying to listen for both location updates and errors (through CLLocationManagerDelegate), and support the ability to track errors but filter them out of the final signal and keep it alive.
When I subscribe to the location signal (via ReactiveCocoaPlayground's -[LocationManager currentLocationSignal]), any errors received will end the signal.
I've tried -catch: and -catchTo: but those just catch one error and then end the signal.
I've tried returning a brand new instance of that signal inside -catch:, but then the error on THAT signal is uncaught (which causes a crash in a RAC() binding later on).
I've tried a recursive approach to that catch as well, which caused a stack overflow (maybe I just made a mistake though).
Is there a way to receive nexts after errors occur?
I believe you're looking for -[RACSignal retry]:
/// Resubscribes to the receiving signal if an error occurs.
- (RACSignal *)retry;