When using word-wide CAS to emulate atomic fetch-and-op, addresses should
be word-aligned to avoid exceptions on some targets.
The problem manifested in a new port I'm working on as a failure in test
gcc.dg/atomic/stdatomic-op-1.c, and I've confirmed that this patch
fixes it. x86_64-unknown-linux still bootstraps, but that is admittedly
of little significance, since that target doesn't use these routines.
FYI, I don't have commit access.
2015-01-09 Andrew Waterman <water...@cs.berkeley.edu>
* fop_n.c (libat_fetch_op): Align address to word boundary.
---
libatomic/fop_n.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/libatomic/fop_n.c b/libatomic/fop_n.c
index 307184d..c2556eb 100644
--- a/libatomic/fop_n.c
+++ b/libatomic/fop_n.c
@@ -112,9 +112,9 @@ SIZE(C2(libat_fetch_,NAME)) (UTYPE *mptr, UTYPE opval, int
smodel)
pre_barrier (smodel);
- wptr = (UWORD *)mptr;
- shift = 0;
- mask = -1;
+ wptr = (UWORD *)((uintptr_t)mptr & -WORDSIZE);
+ shift = (((uintptr_t)mptr % WORDSIZE) * CHAR_BIT) ^ SIZE(INVERT_MASK);
+ mask = SIZE(MASK) << shift;
wopval = (UWORD)opval << shift;
woldval = __atomic_load_n (wptr, __ATOMIC_RELAXED);
--
2.2.1
