SUMMARY
When I set an exception breakpoint, I don't get the exception message. How do I get the exception message? I already know how to get the stack trace, but that doesn't include the exception message.
DETAILS
In the past I developed iOS Apps with Xcode and when there was a problem, I'd get an error/exception. The exception would often have a message like "can't dereference null" or whatever.
Now, using Xcode 4.6.x for the past several weeks I've never gotten an exception message. I'll often get a SIGABRT. I put in the break on exception breakpoint and it will break there, but it's off in some assembly within the iOS SDK and I never get a message.
In fact, I can't remember the last time I saw anything show up in the debugger console.
Did exception info dissappear with the migration to LLVM?
It's very frustrating to have my app just crash in the SDK without knowing why. I check the last function to make sure things are set up correctly (objects allocated, etc) and they are which means I'm left with no clues.
Is it possibly a build setting held over from the past is somehow turning off exception messages?
Please reopen question. It now has an answer!
In the comments an excellent answer has been given. This should be promoted to full answer, and so I can mark the question answered and others who have this common issue can find it. In order for that to happen, the question needs to be reopened! (I'll delete this plea after that happens.)
I will update Jeff's answer here:
To have both the line causing the exception highlighted (and not UIApplicationMain() in main.m) AND to see the reason for the exception (e.g., "error: A fetch request must have an entity."), do this:
In the Breakpoint navigator:
Add (+), Add Exception Breakpoint
Select the new breakpoint, Control-Click, Edit Breakpoint
Add Action
Enter: po $arg1
The relevant part of the stack trace will be in the nagivator area.
This seems to still work in Xcode 9
Here is my addition for use with Xcode 6 and below.
Enter: po (NSException*) $eax
In Xcode 6 you must explicitly provide the object type because it is no longer inferred.
For Xcode 7-9 (based off Jeff's answer):
In the Breakpoint navigator:
Add (+), Add Exception Breakpoint
Select the new breakpoint, Control-Click, Edit Breakpoint
Add Action
Enter: po $arg1
To have both the line causing the exception highlighted (and not UIApplicationMain() in main.m) AND to see the reason for the exception (e.g., "error: A fetch request must have an entity."), do this:
In the Breakpoint navigator:
Add (+), Add Exception Breakpoint
Select the new breakpoint, Contorl-Click, Edit Breakpoint
Add Action
Enter: po $eax
The relevant part of the stack trace will be in the nagivator area.
Yes xcode is not so friendly for debugging. I like this article which helps me to understand crash logs a bit clearly))
Demystifying iOS Application Crash Logs
Also do this if you see error "message sent to deallocated instance"
'Products -> Edit Scheme -> Enable Zombie Objects'
this will enable zombie objects and when you do profile to your project choose
"zombie", cause error and you will be able to see which objects was deallocated e.g NSArray *myArray
The information I get from po $eax or po (NSException *)$eax seems to be different from what Xcode would print if no exception breakpoints are set. So I do the following,
Add an exception breakpoint
Exception occurs, breakpoint was hit -> I know the location
Temporarily disable breakpoints (second button on the left in Debug area)
Continue program execution (third button on the left in Debug area)
Details are printed -> I know the cause
Obviously not very elegant and flexible, but at least I two big questions are answered (where and why).
You can use bt or thread backtrace command to print error trace
Show the stack backtrace for the current thread.
The same stack trace you can find in crash reports
Information about current thread use currentThread
//Objective-C
po [NSThread currentThread]
//Swift
po Thread.currentThread
*Sometimes you can use fr v(or just v from XCode 10.2) when po is not working
Related
I'm stopped at an exception breakpoint. How can I use the LLDB console to tell which exception was thrown?
According to this comment I should be able to type po $r0 to see the exception object "because it is passed as the first argument to objc_exception_throw" but this register doesn't appear to exist on ARM64.
After reading the iOS ABI Function Call Guide I also tried po $x0 but registers x0 through x18 are all empty.
I'm using XCode 5.1, iOS 7.1 on ARM64.
Are you sure you have the correct stack frame selected (i.e. the objc_exception_throw frame)?
According to this answer, your po $x0 should work.
I am new to XCode and Objective C. I have intentionally make a mistake to assign number to NSString*.
NSString* s = #1;
[s uppercaseString];
Though XCode gives me warning, this code will compile. But at runtime I get exception. Now I see in logs, (Sorry for image, I was not able to paste is as text properly due to formatting)
In this log, how I find exact place of error. How this log tells me which code to change.
So it looks like you are running the Release build (debug symbols stripped) and if you got that crash log in a production environment you would need to symbolicate it in order to find the line.
This Apple TN gives some details of Symbolication.
In a development environment you would simply add an exception breakpoint and run it from Xcode, as the debug symbols would not be stripped.
To understand what line causes the problem, you usually need to add exception breakpoint to your project as explained in this document;
In the bottom-left corner of the breakpoints navigator, click the
Add button.
Choose Add Exception Breakpoint.
In the Exception pop-up menu, choose the type of exception on which
you want execution to stop:
All. Stops on all exceptions.
Objective-C. Stops on Objective-C exceptions.
C++. Stops on C++ exceptions. To stop on a particular C++ exception, specify the exception name.
Choose the phase of the exception handling process at which you want program execution to stop.
Click Done.
line 5 Sam : [BIDViewController viewDidLoad] + 143 , if this is a release build , you need to resolve with symbols the memory address of the function , this is called "symbolize" the crash dump...
In the log look for your project name and you will come to know.
e.g.
line 5 Sam : [BIDViewController viewDidLoad] + 143
If you want to produce real crash without warning, try following code it will produce index out of bound exception and will crash
NSArray *array = #[#"1",#"2"];
NSLog(#"Item not accessible->%#",(NSString*)array[2]);
set Exception breaking point or enable NSZombie object
or
NSZombie
From the menu bar, choose Project > Scheme > Edit Scheme
I'm getting the following Exception on iOS6 (on an App with CoreData):
"2012-10-15 10:21:28.952 MyApp[68650:c07] * Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '* -[__NSArrayM insertObject:atIndex:]: object cannot be nil'
* First throw call stack:
(0x28e6012 0x2659e7e 0x2899b6a 0x2899a20 0x1646941 0x1642c67 0x164f846 0x164f908 0x6c540 0x2057e83 0x28a5376 0x28a4e06 0x288ca82 0x288bf44 0x288be1b 0x33967e3 0x3396668 0x15a165c 0x13a22 0x2845)
libc++abi.dylib: terminate called throwing an exception"
This doesn't happen on iOS5, so something happens on iOS6 what I don't understand.
I set a Breakpoint on every point where I call insertObject:atIndex: but these are not called - it have to be something in this libc++abi.dylib which gets called and crashes.
Does anyone know what could be wrong?
thank you
This is probably because either iOS5 did not throw an exception for this error (and should have, but now iOS6 throws one which is better than having erratic behavior later), or because you have some different behavior in iOS6 which makes your object nil whereas it was not in iOS5.
Whatever the reason, you can add a Symbolic Breakpoint on the insertObject:atIndex: symbol, so that it will break every time this method is called, wherever it is in your application (in your own code or not).
Go to the "Breakpoints Navigator" view (Cmd-6 shortcut)
Click on the "+" button to add a symbolic breakpoint
Set the symbolic breakpoint to break when it hits the symbol [NSArray insertObject:atIndex:]
Thus you can see when this is called with a nil value for the first parameter and fix your problem where it occurs.
You can also instead add an Exception Breakpoint to break when an exception is thrown, thus knowing when in the code your exception occurs. This is another way to let you know which part of the code (your own or another) generate the exception.
Once the breakpoint has been hit and the program stops before the exception occurs, you can check in the call stack what part of your own code led to trigger this exception at the end.
The reason for the crash is that the object you are trying to insert is nil. This means it is not properly instantiated. This in turn means something has gone awry before you reached that exception.
Could you post the code that alloced and initialized the object you were trying to insert?
In order to find the relevant line of code, please try the following: Go to the "Exception" tab in your Xcode project:
Then click the "+" button (at the bottom of the page) and select "Add Exception Breakppoint ...". Leave all settings to their defaults and click "Done".
If you rerun your project it should now stop at the relevant line of code before the exception is thrown. Then you can move up the call-stack and identify from where in your code you called the library function that is responsible for this behavior. Then try to see if all objects are correctly initialized at this point.
Using Xcode 4.3.2. I looked at many different similar issues including this one
no-call-stack-on-exception-in-xcode-4
but cannot get the debugger (gdb or lldb) to give me a good stack trace that shows the location of the exception AND to also prints what the exception is
Setting either a symbolic exception on objc_exception_throw or an "All Exceptions" exception breakpoint, lldb would not give me a good stack trace but would show the following:
thread #1: tid = 0x1c03, 0x34455238 libobjc.A.dylibobjc_exception_throw, stop reason = breakpoint 1.1
frame #0: 0x34455238 libobjc.A.dylibobjc_exception_throw
frame #1: 0x323ff788 CoreFoundation`+[NSException raise:format:arguments:] + 100
That is the whole thing, either through bt or at full magnification in the graphical breakpoint/debugger view.
If I hit continue a few time at this point it will eventually tell me the exception/assertion, for example
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '_endUndoGroupRemovingIfEmpty:: NSUndoManager 0x2b7610 is in invalid state, endUndoGrouping called with no matching begin
But I have no idea where it is at.
gdb, using the same breakpoint, WILL stop and show me where it is at, but does not print the exception text. If I hit continue a few times it does but I have lost my context of the back trace.
I would like to know how to print the exception text so I know WHY it stopped, without having to do a few continues and losing my place. I would also like to get it to stop in lldb at the point of the exception like it does in gdb.
Please try updating to Xcode 4.5. You're seeing an armv7 unwinder problem where lldb doesn't know how to unwind your stack completely. The Objective-C runtime has some functions that are difficult to unwind out of (hand-written assembly) but I just did a quick test on an iOS device with Xcode 4.5 and lldb behaved correctly when I had Xcode set an Exception Breakpoint on throw.
Background
We have a problem that sometimes the grid in Devexpress raise exception
"Raised EConvertError: Cannot assign a nil to a TFont".
But to trace the real cause of this we have changed Font in cxEdit to be a public property instead with a get and set method. Here I want to log the callstack.
My question
Normally JCL is used to log callstacks when exceptions appear. But how can I log the callstack without using raise exception and show a dialog for the user about this ?
I have found the lines:
var
GlobalStackList: TJclGlobalStackList;
in JclDebug but I fail to use it. If someone have a example how to get the callstack I would be happy.
Regards Roland Bengtsson
This answer shows how to do it with JCL by calling JclCreateStackList.