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From: Marcel Moolenaar <marcel@FreeBSD.org>
Date: Wed, 28 May 2008 16:41:02 +0000 (UTC)
To: src-committers@FreeBSD.org, cvs-src@FreeBSD.org, cvs-all@FreeBSD.org
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Cc: 
Subject: cvs commit: src/sys/ia64/include atomic.h
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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