Another unwinding problem on ARM

[Mathias Bauer]

Hi dear list members,

the tests in GNUstep base revealed another problem that is related to 
unwinding. libobjc2 and gnustep base have been built with the latest 
llvm/clang trunk version and with -fobjc_runtime=gnustep-1.7.

The test core/base/Tests/base/NSOperation/obj/threads produces a crash 
when a thread is exited.

The first thread in this test case that was exited seemed to get 
unwinded somehow. This is the call stack I got before it ended:

> #0  0xb4fcb064 in siglongjmp () from /lib/libc.so.6
> #1  0xb651a3d0 in unwind_stop () from /lib/libpthread.so.0
> #2  0xb50f4808 in ?? () from /lib/libgcc_s.so.1
> #3  0xb50f5550 in _Unwind_ForcedUnwind () from /lib/libgcc_s.so.1
> #4  0xb651cb64 in _Unwind_ForcedUnwind () from /lib/libpthread.so.0
> #5  0xb651a47c in __pthread_unwind () from /lib/libpthread.so.0
> #6  0xb6513f40 in pthread_exit () from /lib/libpthread.so.0
> #7  0xb6d0c99c in +[NSThread exit] (self=0xb6f8c4b0 <_OBJC_CLASS_NSThread>, 
> _cmd=0xb6f8c6d8 <.objc_selector_list+168>) at NSThread.m:535
> #8  0xb6d0e4a4 in nsthreadLauncher (thread=0x10fca0) at NSThread.m:811
> #9  0xb6512e2c in start_thread () from /lib/libpthread.so.0

The personality routine in libobjc2 was not called here. It is called 
however if I do the same test on Linux X86_64.

Shouldn't we expect that the Objective-C personality routine will be 
called on ARM also?

For me it looks as if the stack unwinding was ended prematurely, before 
a stack frame with Objective-C code was hit. But it may be just my 
limited understanding that lets me think so.

The second thread to be exited hits a breakpoint in unwind_stop several 
times and then finally ends up in a SIGABRT:

> #0  0xb4fcb240 in raise () from /lib/libc.so.6
> #1  0xb4fcc66c in abort () from /lib/libc.so.6
> #2  0xb651a480 in __pthread_unwind () from /lib/libpthread.so.0
> #3  0xb6513f40 in pthread_exit () from /lib/libpthread.so.0
> #4  0xb6d0c99c in +[NSThread exit] (self=0xb6f8c4b0 <_OBJC_CLASS_NSThread>, 
> _cmd=0x1c8b0 <.objc_selector_list+32>) at NSThread.m:535
> #5  0x0000a810 in -[OpExit main] (self=0x1001b8, _cmd=0xb6f79738 
> <.objc_selector_list+312>) at threads.m:92
> #6  0xb6c70cf0 in -[NSOperation start] (self=0x1001b8, _cmd=0x1c8f8 
> <.objc_selector_list+104>) at NSOperation.m:463
> #7  0xb6c6be10 in -[NSObject performSelector:withObject:] (self=0x1001b8, _cmd=0xb6f8c720 
> <.objc_selector_list+240>, aSelector=0x1c8f8 <.objc_selector_list+104>, 
> anObject=0x0) at NSObject.m:2046
> #8  0xb6d0da90 in -[NSThread main] (self=0x113960, _cmd=0xb6f8c638 
> <.objc_selector_list+8>) at NSThread.m:743
> #9  0xb6d0e474 in nsthreadLauncher (thread=0x113960) at NSThread.m:809
> #10 0xb6512e2c in start_thread () from /lib/libpthread.so.0

Does someone have an idea for the reason of that or where to look to get 
more information about possible root causes ?

Regards,
Mathias