Date: Wed, 28 May 2008 16:41:02 +0000 (UTC) From: Marcel Moolenaar <marcel@FreeBSD.org> To: src-committers@FreeBSD.org, cvs-src@FreeBSD.org, cvs-all@FreeBSD.org Subject: cvs commit: src/sys/ia64/include atomic.h Message-ID: <200805281641.m4SGf3ix052304@repoman.freebsd.org>
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marcel 2008-05-28 16:41:02 UTC
FreeBSD src repository
Modified files:
sys/ia64/include atomic.h
Log:
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.
The work-around is to zero-extend by casting to uint64_t.
Revision Changes Path
1.14 +1 -1 src/sys/ia64/include/atomic.h
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