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")
/*
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