Re: Another unwinding problem on ARM

[Mathias Bauer]

Am 14.03.14 13:56, schrieb Mathias Bauer:
> Hi,
>
> once you find it, the solution quite often is easy. :-)
>
> The culprit was that unwind-arm.h in libobjc2 can't cope with unwind
> states that have been "or-ed" with _US_FORCE_UNWIND.
>
> Defining it in this file and replacing
>
> switch(state)
>
> with
>
> switch(state & ~_US_FORCE_UNWIND)
>
> helps.
>
> Without that, the PR wrapper in this header file always returns
> _URC_FAILURE. I overlooked that in the first place because I only looked
> whether internal_objc_personality was called.
>
> Now the test case works - at least when run inside gdb. I still have to
> find out why it core dumps without gdb.

And this turns out to be a problem of interpreting the LSDA.

The stack frame in question belongs to [NSOperation start].
When the PR __gnu_objc_personality_v0 is called for it, the 
internal_objc_personality function calls check_action. The 
resolve_indirect_value function returns something that - when 
interpreted as a char* - leads to a crash.

I wonder whether the internal_objc_personality needs some adjustments 
for _US_FORCE_UNWIND here.

I will continue investigating this, but I would appreciate any hints 
that could help me speed this up. My wife probably will get angry if it 
takes the whole weekend. ;-)

Regards,
Mathias