I did something in IDE options, and after some time this window became always empty. Does anybody knows what's the deal?
To test I do something simple like this
app.log('crash test '+inttostr(1 div JvTrayIcon1.IconIndex));
...and it rises, asks me to break, I do break, and.. there is nothing in Call Stack. But I remember it worked, and worked amazingly fine...
I got it! highly likely it is just IDE bug. Just do not detach this window. Return it back to main desktop flow. And it will work again.
I am trying to debug a small prototype for an iPhone App (iOS Simulator 4.1), compiled as Debug, with all the configuration apparently ok.
The application makes use of Cocos2d graphic engine and GDataXMLNode library (for XML reading). There isn’t much stuff going on. But on certain method, if I set a breakpoint, gdb simply “stops”.
Here’s the status line of the debugger after it hits he breakpoint:
And here’s the code that has the breakpoint(sshot):
note: the breakpoint could be anywhere in that function and it’s the same.
And this is the calling code (from another object)
self.map = [SimulationLoader loadMap];
None of the Editor buttons work when a breakpoint is set inside the “loadMap" (step into, step out, next, continue execution, etc.). I can stop and/or restart the debugging and it works (but goes back to the beginning). The gdb prompt, will let me write, but nothing happens. I cannot view object values or anything debugging related. I cannot resume execution, it won’t do anything.
The strange thing is that, if I put a breakpoint before or after that line (the loadMap), it all works, and I can step out or in, debug it and do all I want to do.
What am I missing?
A couple of seconds after the “failing” breakpoint is hit (and it “hangs”) the stack window clears. I believe all this happens because the gdb has stopped, but the question is, why does it stop there? What are the restrictions for this?
I’m compiling with LLVM GCC 4.2 for what is worth (but could probably change to other if that’s the problem, haven’t tried that because I don’t know much about the differences).
Is there something (maybe in your Map class?) that requires timing? For instance, a double-tap that's being interrupted by the breakpoint's being triggered at that spot?
(i.e., no breakpoint => double-tap registered, Breakpoint => second tap comes after breakpoint hits, so only a single-tap is registered.)
I don't see anything like this in your code specifically, but that's the kind of thing that could show mysteriously different behavior between breakpoints on/off.
While debugging the program my breakpoint is not working, so please give me some advice so that it can work properly.
Maybe you've tried to use the breakpoint on unreachable code? Try setting your breakpoint somewhere before the point you want to reach and try stepping from there to see if the point is actually reached.
Possible Reasons could be.
1. After changes in the code you have not built the libraries properly so the breakpoint is not pointing to the right location in the code.
2. If you are putting a breakpoint in a library then make sure the library is build and is built in Debug mode.
3. Clean full environment and rebuild the project.
Open XCode preferences and in the Debugging tab, un-check "Load symbols lazily", this caught me out when I first started iPhone developement. Then again, it might be for any of the other reasons that people have already mentioned.
Most of the times when Iphone program crash, compiler show stack with full of no's, but these no's don't make any sense to me. Very rarely it point out where the problem might be and mostly there are these useless no's. How you can make sure that when your program crashes while development/testing, it shows at what place this cause this crash?
My iPhone dev life was horrible until I found NSZombieEnabled. By adding this flag into your executable, it will help you see any memory issues by letting you know what the name of the object that is at fault is.
This works by never actually releasing an object, but by wrapping it up as a "zombie" and setting a flag inside it that says it normally would have been released. This way, if you try to access it again, it still know what it was before you made the error, and with this little bit of information, you can usually backtrack to see what the issue was.
It especially helps in background threads when the Debugger sometimes craps out on any useful information.
VERY IMPORTANT TO NOTE however, is that you need to 100% make sure this is only in your debug code and not your distribution code. Because nothing is ever release, your app will leak and leak and leak. To remind me to do this, I put this log in my appdelegate:
if(getenv("NSZombieEnabled") || getenv("NSAutoreleaseFreedObjectCheckEnabled"))
NSLog(#"NSZombieEnabled/NSAutoreleaseFreedObjectCheckEnabled enabled!");
The key word you are looking for is "symbolicate". If you have a crash log from a device, you have to sun symbolicate on it in order to have the stack trace give you line numbers.
The function I have in my .profile to help me run the command is:
function desym
{
/Developer/Platforms/iPhoneOS.platform/Developer/Library/PrivateFrameworks/DTDeviceKit.framework/Versions/A/Resources/symbolicatecrash -A -v $1 | more
}
Basically you put the app bundle, the dsym file generated at build, and the crash log in the same directory and then run "dysm [CrashLog File Name]" to have the symbols correctly shown in the stack trace.
Note that it must be the same executable and dysm file that generated the crash! Every time you recompile, locations of things can change.
Things to do:
1) Debug with breakpoint on
2) Add a global breakpoint: objc_exception_throw
Then look in the Debugger window
I'm programming an application in Objective-C and I'm getting this error:
MyApp(2121,0xb0185000) malloc: *** error for object 0x1068310: double free
*** set a breakpoint in malloc_error_break to debug
It is happening when I release an NSAutoreleasePool and I can't figure out what object I'm releasing twice.
How do I set his breakpoint?
Is there a way to know what is this "object 0x1068310"?
When an object is "double-freed", the most common cause is that you're (unnecessarily) releasing an autoreleased object, and it is later autoreleased when the containing autorelease pool is emptied.
I've found that the best way to track down the extra release is to use the NSZombieEnabled environment variable for the affected executable in Xcode. For a quick rundown of how to use it, check out this CocoaDev wiki page. (In addition to this page, Apple has documented some incredibly obscure yet useful tips for debugging code in Xcode, some of which have saved my bacon more than a few times. I suggest checking out this Technical Note on developer.apple.com — link jumps to the section on Cocoa's Foundation framework).
Edit: You can often track the offending object down within the Xcode debugger, but it's often much easier if you use Instruments to assist you. From Xcode, choose Run → Start With Performance Tool → Object Allocations and you should be able to trace the offending object back to where it was created. (This will work best if you're enabled zombies as discussed above.) Note: Snow Leopard adds a Zombies tool to Instruments, accessible from the Run menu as well. Might be worth the $29 alone! ;-)
There is also a related SO question here.
You'll find out what the object is when you break in the debugger. Just look up the call stack and you will find where you free it. That will tell you which object it is.
The easiest way to set the breakpoint is to:
Go to Run -> Show -> Breakpoints (ALT-Command-B)
Scroll to the bottom of the list and add the symbol malloc_error_break
I just want to add my experience in addition to the answer of Quinn Taylor.
In one of my apps, I have to parse and save data into core data objects and later on get these objects to display on the views. In fact, the app works just fine and does not crash at all, until I tried to do a stress test of navigating back and forth multiple times, tried to open multiple views as fast as possible. The app crashes with the above message.
I have tried all the methods that Quinn suggested in his answer and still failed to find out where was the exact cause.
I set NSZombieEnabled=YES, and NSStackLogging=YES, ran the command shell malloc_history to find out why, but still no luck. It always points out to where I save the data into core data objects, in fact, I have checked thousand times the over released objects there, nothing odd.
Running in Instruments with various tools(Allocations, Leaks, etc...) still did not help. Enable the Guard Malloc still got nothing.
Final rescue: I tried to come back to the views where the objects were taken from Core Data and sent a retain message to all of these objects, and took note to these changes. It solved the issue!!!
So, I found out that I failed to retain one, that's exactly the cause. Just want to share my experience so you have another rescue for your app.
Open up the debugger console by pressing Cmd+Shift+R. There, type
break malloc_error_break
to set a breakpoint at the beginning of the malloc_error_break function.
If you want to find out what object is located at address 0x1068310, you can type the following into the debugger console:
print-object 0x1068310
Of course, you have to do this while the object is still alive -- if the object has already been freed by the time you do this, then this will not work.
Please find the below steps for how to find the object which is free and crash the application.
1) Click on the "Breakpoint navigator". 2) Then click on the
"+" button which is below. 3) Add the "Symbolic
Breakpoint..." from the list. 4) Add the
"malloc_error_break" keyword on the "Symbol" option.
Or you can also refer the below GIF presentation.
For me the issue was solved by
(gdb) call (void)_CFAutoreleasePoolPrintPools()
right after the crash. The address at the top of the stack was the address of the culprit. Threw in a retain and voila.
The address given in the log message did not get me anywhere. It never showed up in any of the various Instrumets. Apparently a pointer to some internal data which had already been freed.
Adding a symbolic breakpoint in Xcode 4
Just an update to make this relevant to Xcode 4...
From the Xcode 4 User Guide:
To add a symbolic breakpoint . . .
In the bottom-left corner of the breakpoint navigator, click the Add
button.
Choose Add Symbolic Breakpoint.
Enter the symbol name in the
Symbol field.
Click Done.
This is what the malloc_error_break breakpoint looks like in the Breakpoints window in Xcode.
Need to check the boxes to make it work.
alt text http://www.martijnthe.nl/wp-content/uploads/2009/08/Afbeelding-1.png
Check your classes and look under the dealloc method. Make sure you care calling [super dealloc].
I had this exact same problem and found out I was calling [self dealloc] instead. Just not paying attention.
In Xcode, click left of the line number to set a breakpoint. Then you can launch it by doing a "Build and Debug".
It is recommended to not have object that you create be autorelease since memory is a commodity on the iPhone. Apple recommends explicitly calling release.
To find these kinds of memory and pointer problems in general, you want to run your code against a runtime memory error checker like Valgrind. This should be able to point out lots of things your code is doing wrong, beyond those that cause it to crash.
Valgrind can work on OSX (though it says it's "unsupported and incomplete and buggy"), and with a little hacking someone got it to work on iPhone SDK executables.
Even better you can try Instruments, which is part of XCode. There's a tutorial for running it here.
If malloc_error_break is not helping...
The best way to solve this error is to run instruments with the NSZombies turned on. Instruments will flag you when the Zombie is messaged and you can trace directly back to the line of code.
Snow Leopard required, what a lifesaver though!
This is usually caused by some inspector, such as safari or safari preview. Refer to post or post and question.
Remove the select of AutoMatically Show Web ...., will remove this issue.
Note, just close safari or safari preview will not remove this issue. And you have to deselect both of safari and safari preview.
If this will not do, refer to this answer or post to debug it.