Add libatomic as a target library.

From-SVN: r187018

1 files changed, 115 insertions, 0 deletions

diff --git a/libatomic/load_n.c b/libatomic/load_n.c
new file mode 100644
index 0000000..a48f256
--- /dev/null
+++ b/libatomic/load_n.c
@@ -0,0 +1,115 @@
+/* Copyright (C) 2012 Free Software Foundation, Inc.
+   Contributed by Richard Henderson <rth@redhat.com>.
+
+   This file is part of the GNU Atomic Library (libatomic).
+
+   Libatomic is free software; you can redistribute it and/or modify it
+   under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   Libatomic is distributed in the hope that it will be useful, but WITHOUT ANY
+   WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+   FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+   more details.
+
+   Under Section 7 of GPL version 3, you are granted additional
+   permissions described in the GCC Runtime Library Exception, version
+   3.1, as published by the Free Software Foundation.
+
+   You should have received a copy of the GNU General Public License and
+   a copy of the GCC Runtime Library Exception along with this program;
+   see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include "libatomic_i.h"
+
+
+/* If we support the builtin, just use it.  */
+#if !DONE && SIZE(HAVE_ATOMIC_LDST)
+UTYPE
+SIZE(libat_load) (UTYPE *mptr, int smodel)
+{
+  if (maybe_specialcase_relaxed(smodel))
+    return __atomic_load_n (mptr, __ATOMIC_RELAXED);
+  else if (maybe_specialcase_acqrel(smodel))
+    /* Note that REL and ACQ_REL are not valid for loads.  */
+    return __atomic_load_n (mptr, __ATOMIC_ACQUIRE);
+  else
+    return __atomic_load_n (mptr, __ATOMIC_SEQ_CST);
+}
+
+#define DONE 1
+#endif /* HAVE_ATOMIC_LOAD */
+
+
+/* If we have compare-and-swap, use it to swap 0 with 0 and as a side
+   effect load the original value.  */
+#if !DONE && defined(atomic_compare_exchange_n)
+UTYPE
+SIZE(libat_load) (UTYPE *mptr, int smodel)
+{
+  UTYPE t = 0;
+
+  if (maybe_specialcase_relaxed(smodel))
+    atomic_compare_exchange_n (mptr, &t, 0, true,
+			       __ATOMIC_RELAXED, __ATOMIC_RELAXED);
+  else if (maybe_specialcase_acqrel(smodel))
+    atomic_compare_exchange_n (mptr, &t, 0, true,
+			       __ATOMIC_ACQ_REL, __ATOMIC_ACQ_REL);
+  else
+    atomic_compare_exchange_n (mptr, &t, 0, true,
+                               __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);
+
+  return t;
+}
+
+#define DONE 1
+#endif /* atomic_compare_exchange_n */
+
+
+/* Similar, but only assume a word-sized compare-and-swap.  */
+#if !DONE && N < WORDSIZE && defined(atomic_compare_exchange_w)
+UTYPE
+SIZE(libat_load) (UTYPE *mptr, int smodel)
+{
+  UWORD shift, t, *wptr;
+
+  pre_barrier (smodel);
+
+  wptr = (UWORD *)((uintptr_t)mptr & -WORDSIZE);
+  shift = (((uintptr_t)mptr % WORDSIZE) * CHAR_BIT) ^ SIZE(INVERT_MASK);
+
+  /* Exchange 0 with 0, placing the old value of *WPTR in T.  */
+  t = 0;
+  atomic_compare_exchange_w (wptr, &t, 0);
+
+  post_barrier (smodel);
+  return t >> shift;
+}
+
+#define DONE 1
+#endif /* HAVE_ATOMIC_CAS && N < WORDSIZE */
+
+
+/* Otherwise, fall back to some sort of protection mechanism.  */
+#if !DONE
+UTYPE
+SIZE(libat_load) (UTYPE *mptr, int smodel)
+{
+  UTYPE ret;
+  UWORD magic;
+
+  pre_seq_barrier (smodel);
+  magic = protect_start (mptr);
+
+  ret = *mptr;
+
+  protect_end (mptr, magic);
+  post_seq_barrier (smodel);
+
+  return ret;
+}
+#endif
+
+EXPORT_ALIAS (SIZE(load));