svn commit: r185526 - in stable/7/sys: . ia64/include

Wilko Bulte wb at
Mon Dec 1 14:03:05 PST 2008

Quoting Marcel Moolenaar, who wrote on Mon, Dec 01, 2008 at 05:40:57PM +0000 ..
> Author: marcel
> Date: Mon Dec  1 17:40:57 2008
> New Revision: 185526
> URL:
> Log:
>   MFC rev 179382:
>   Work-around a compiler optimization bug, that broke libthr. Massive
>   inlining resulted in constant propagation to the extend that cmpval
>   was known to the compiler to be URWLOCK_WRITE_OWNER (= 0x80000000U).
>   Unfortunately, instead of zero-extending the unsigned constant, it
>   was sign-extended. As such, the cmpxchg instruction was comparing
>   0x0000000080000000LU to 0xffffffff80000000LU and obviously didn't
>   perform the exchange.
>   But, since the value returned by cmpxhg equalled cmpval (when zero-
>   extended), the _thr_rtld_lock_release() function thought the exchange
>   did happen and as such returned as if having released the lock. This
>   was not the case. Subsequent locking requests found rw_state non-zero
>   and the thread in question entered the kernel and block indefinitely.


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