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

[Marcel Moolenaar]

Author: marcel
Date: Mon Dec  1 17:40:57 2008
New Revision: 185526
URL: http://svn.freebsd.org/changeset/base/185526

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.
  
  The work-around is to zero-extend by casting to uint64_t.
  
  Approved by:	re (kensmith)

Modified:
  stable/7/sys/   (props changed)
  stable/7/sys/ia64/include/atomic.h

Modified: stable/7/sys/ia64/include/atomic.h
==============================================================================
--- stable/7/sys/ia64/include/atomic.h	Mon Dec  1 17:39:34 2008	(r185525)
+++ stable/7/sys/ia64/include/atomic.h	Mon Dec  1 17:40:57 2008	(r185526)
@@ -42,7 +42,7 @@
 		"mov ar.ccv=%2;;\n\t"					\
 		"cmpxchg" #sz "." #sem " %0=%4,%3,ar.ccv\n\t"		\
 		: "=r" (ret), "=m" (*p)					\
-		: "r" (cmpval), "r" (newval), "m" (*p)			\
+		: "r" ((uint64_t)cmpval), "r" (newval), "m" (*p)	\
 		: "memory")
 
 /*