Re: NSHashTable with weak objects crashing

[Frederik Seiffert]

Thanks for the suggestion Jordan. That’s certainly concerning to hear about the segfaults you’re experiencing with weak references. Is this on ARMv7 only and do you think it could be related to the WeakReferences test failing (https://github.com/gnustep/libobjc2/issues/107)?

I tried out using the reference implementation for the runtime but it doesn’t make a difference for the NSHashTable issue.

Frederik

Am 30.07.2019 um 06:55 schrieb Jordan Schidlowsky <jordan@noodlecake.com>:

worth a shot, but for whatever reason, we seem to experience heap-use-after-free segfaults when using weak references under ARC in the current libobjc2 runtime.  

I replace the following functions with their reference implementations below, and it seems to solve our seg-fault issues using weak references under arc:

https://clang.llvm.org/docs/AutomaticReferenceCounting.html#arc-runtime-objc-initweak

objc_copyWeak

objc_destroyWeak

objc_initWeak

objc_loadWeak

-Jordan

On Jul 29, 2019, at 8:38 AM, Frederik Seiffert <frederik@algoriddim.com> wrote:

Hi,

I’m trying to use an NSHashTable with weak objects (-weakObjectsHashTable) on Android, but it’s segfaulting in addObject: on all architectures (ARM/x86). Does anyone know if this should be supported or what might be going on here?

Following is the backtrace:

    frame #5: 0xca4e2b12 libobjc.so`objc_msgSend at objc_msgSend.x86-32.S:120

    frame #6: 0xc9befbcd libgnustep-base.so`hashObject(item=0xcacce5a0, size=0x00000000) at NSConcretePointerFunctions.m:126

    frame #7: 0xc9b02992 libgnustep-base.so`pointerFunctionsHash(PF=0xc7d2d210, item=0xcacce5a0) at NSConcretePointerFunctions.h:180

    frame #8: 0xc9aff7b6 libgnustep-base.so`GSIMapBucketForKey(map=0xc7d2d1e4, key=GSIMapKey @ 0xfff875b4) at GSIMap.h:410

    frame #9: 0xc9b02c03 libgnustep-base.so`GSIMapAddNodeToMap(map=0xc7d2d1e4, node=0xcacce590) at GSIMap.h:453

    frame #10: 0xc9afe964 libgnustep-base.so`GSIMapAddKey(map=0xc7d2d1e4, key=GSIMapKey @ 0xfff87644) at GSIMap.h:1118

    frame #11: 0xc9b0074f libgnustep-base.so`-[NSConcreteHashTable addObject:](self=0xc7d2d1e4, _cmd="C", anObject=0xcac9945c) at NSConcreteHashTable.m:863

Interestingly, when I use hashTableWithWeakObjects (NSPointerFunctionsZeroingWeakMemory, deprecated on Apple platforms) instead of weakObjectsHashTable (NSPointerFunctionsWeakMemory), addObject: works OK, but the pointer is not zero’d when the object is released.

Thanks!

Frederik

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