Re: Exceptions in GNUstep

[Fred Kiefer]

On 02.08.2013 16:36, Riccardo Mottola wrote:
> Hi,
> 
> I have a hard time analyzing certain runtime exceptions in GNUstep. For
> example, if you send a message to a non-existing method under Cocoa, you
> get an NSLog, not so on GS, at least, not always. I am speaking of a Gui
> app.
> 
> Right now, I don't have a "cocoa" counterpart of the Application I'm
> trying to debug, so...
> 
> I know I get an exception, because I noticed the app misbehaving, thus I
> put a breakpoi8nt in [NSException raise] and rightfully it stops:
> 
> Breakpoint 2, 0xb6f7fd50 in -[NSException raise] (self=0xa409f28,
>     _cmd=0xb72521c0) at NSException.m:1056
> 1056      id    info = (_reserved == 0) ? nil : _e_info;
> 
> trace:
> 
> (gdb) bt
> #0  0xb6f7fd50 in -[NSException raise] (self=0xa409f28, _cmd=0xb72521c0)
>     at NSException.m:1056
> #1  0xb6f7f2c9 in +[NSException raise:format:arguments:] (self=0xb7252260,
>     _cmd=0xb72521a8, name=0xb7252294, format=0xb726d4c0,
>     argList=0xbfe8b310
> "ÿ÷\"·Ó\017\017·Ê\207&·Ìçý¶\221²è¿\233²è¿Ê\207&·ð\001ø¶\020;C\n\220j*·xj*·")
> at NSException.m:1056
> #2  0xb6f80245 in +[NSException raise:format:] (self=0xb7252260,
>     _cmd=0xb726d280, name=0xb7252294, format=0xb726d4c0) at
> NSException.m:1056
> #3  0xb6fdd69c in -[NSObject doesNotRecognizeSelector:] (self=0xa416c00,
>     _cmd=0xb726d370, aSelector=0xb7268d10) at NSObject.m:1425
> #4  0xb6fdbb69 in -[NSObject forwardInvocation:] (self=0xa416c00,
>     _cmd=0xb72a6ab0, anInvocation=0xa433b10) at NSObject.m:1765
> #5  0x0a416c00 in ?? ()
> #6  0xb726d370 in _OBJC_SELECTOR_TABLE ()
>    from /System/Library/Libraries/libgnustep-base.so.1.24
> #7  0xb7268d10 in _OBJC_SELECTOR_TABLE ()
>    from /System/Library/Libraries/libgnustep-base.so.1.24
> #8  0xb6f9f246 in -[NSInvocation setTarget:] (self=0x5c891cec,
>     _cmd=0xdfe81024, anObject=0x81ffece8) at GSPrivate.h:101
> Backtrace stopped: previous frame inner to this frame (corrupt stack?)
> 
> 
> this gives me no real clue about where this is coming from and what is
> the missing selector and where it is trying to access it. I guess it is
> a wrong selector because of "doesNotRecognizeSelector".
> 
> I tried getting up to stack #3 and print out the selector, which is a
> (SEL). How may I print it out?
> 
> However, the next step is why I get no output.
> 
> I put a breakpoint in _NSAppKitUncaughtExceptionHandler() of
> NSApplication. That exception will either re-raise it through base if
> there is no graphic context or put a nice Panel. In theory. I don't get
> into that method, this means the exception is sort trapped elsewhere or
> not thrown in a way that ends up here!
> 
> Ideas?

Hi Riccardo,

please have a look at this method in NSApplication:

- (void) _handleException: (NSException *)exception

As you can see it gets the mask for exception handling from the
defaults. My current setting there is 3, which means I get a log and the
exception ends up in a panel. This is the best setting for a development
environment, but not what you want on a user desktop.

On your second question, how to print out a selector. It is as easy as
po NSStringFromSelector(aSelector)

But don't be surprised when you don't get a useful result. Your stack
seems to be already corrupted.

Hope this helps,
Fred