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Re: Mysterious crash in NSRunLoop, using libobjc2 on Linux


From: David Chisnall
Subject: Re: Mysterious crash in NSRunLoop, using libobjc2 on Linux
Date: Mon, 11 Dec 2017 17:01:38 +0000

On 11 Dec 2017, at 16:57, Lobron, David <address@hidden> wrote:
> 
>>> Thanks, David!  I will try to make a reduced test case, based on this.  
>>> I'll start with a simple program that throws an ObjC exception in an 
>>> NS_HANDLER, where the whole thing resides in a .mm file.  BTW, I've enabled 
>>> native exceptions here.  I will let you guys know when I've got something.
>> 
>> Just use @try and @catch.  If you can find a smallish test case, please file 
>> a bug on GitHub and I’ll take a look.  Ideally, a test case shouldn’t depend 
>> on anything other than libobjc2 - take a look at the existing EH tests and 
>> see if you can make a similar one that shows the issue.
> 
> I've been trying combinations of C++ and ObjC exceptions in a .mm file, and 
> so far I haven't been able to reproduce the abort behavior.  I've attached my 
> latest code, which throws ObjC and C++ exceptions from C++ and ObjC classes, 
> and catches them.  Please let me know if you can think of any variations I 
> haven't tried here.  
> 

If the failure is what I suspect that it is, then it’s a problem caused by 
mixing C++ and Objective-C exception unwinding, so it won’t be possible to 
reproduce in a single file.  You will need to throw an exception from 
Objective-C++ and have it pass through stack frames from an Objective-C 
compilation unit that includes an @finally block that runs some code, and then 
be caught in an Objective-C++ compilation unit.  

David




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