[ltt-dev] [PATCH] fix the "unknown" case

[Paul E. McKenney]

Use a back-to-back pair of pthread_mutex_lock acquisitions and releases
to stand in for a memory barrier, given that ARM doesn't always seem to do
the right thing with __sync_synchronize().  Tested on ARM and on x86.
The x86 testing was performed by removing all of the x86-specific
tests from configure.ac and then building from scratch.

Signed-off-by: Paul E. McKenney <paulmck at linux.vnet.ibm.com>
---

 configure.ac                |    9 +---
 urcu/arch_unknown.h         |   87 ++++++++++++++++++++++++++++++++++++++++++++
 urcu/uatomic_arch_unknown.h |   57 ++++++++++++++++++++++++++++
 3 files changed, 146 insertions(+), 7 deletions(-)

diff --git a/configure.ac b/configure.ac
index 1b1ca65..9274337 100644
--- a/configure.ac
+++ b/configure.ac
@@ -54,13 +54,8 @@ case $host_cpu in
 	*) ARCHTYPE="unknown";;
 esac
 
-if test "$ARCHTYPE" != "unknown"; then
-	UATOMICSRC=urcu/uatomic_arch_$ARCHTYPE.h
-	ARCHSRC=urcu/arch_$ARCHTYPE.h
-else
-	UATOMICSRC=urcu/uatomic_generic.h
-	ARCHSRC=urcu/arch_generic.h
-fi
+UATOMICSRC=urcu/uatomic_arch_$ARCHTYPE.h
+ARCHSRC=urcu/arch_$ARCHTYPE.h
 if test "x$ARCHTYPE" != xx86 -a "x$ARCHTYPE" != xppc; then
 	APISRC=tests/api_gcc.h
 else
diff --git a/urcu/arch_unknown.h b/urcu/arch_unknown.h
new file mode 100644
index 0000000..3f78310
--- /dev/null
+++ b/urcu/arch_unknown.h
@@ -0,0 +1,87 @@
+#ifndef _URCU_ARCH_ARMV7_H
+#define _URCU_ARCH_ARMV7_H
+
+/*
+ * arch_armv7.h: trivial definitions for the ARMv7-A/R architecture.
+ *
+ * Copyright (c) 2010 Paul E. McKenney, IBM Corporation.
+ * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers at polymtl.ca>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+*
+ * This library 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <urcu/compiler.h>
+#include <urcu/config.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif 
+
+/* We don't know, so guess!!! */
+#define CACHE_LINE_SIZE	64
+
+#define mb()    \
+	do { \
+		pthread_mutex_t __mb_fake_mutex; \
+		\
+		pthread_mutex_init(&__mb_fake_mutex, NULL); \
+		if (pthread_mutex_lock(&__mb_fake_mutex) != 0) { \
+			perror("pthread_mutex_lock"); \
+			abort(); \
+		} \
+		if (pthread_mutex_unlock(&__mb_fake_mutex) != 0) { \
+			perror("pthread_mutex_lock"); \
+			abort(); \
+		} \
+		if (pthread_mutex_lock(&__mb_fake_mutex) != 0) { \
+			perror("pthread_mutex_lock"); \
+			abort(); \
+		} \
+		if (pthread_mutex_unlock(&__mb_fake_mutex) != 0) { \
+			perror("pthread_mutex_lock"); \
+			abort(); \
+		} \
+	} while (0)
+
+/*
+ * Serialize core instruction execution. Also acts as a compiler barrier.
+ */
+#define sync_core()	asm volatile("isb" : : : "memory")
+
+#include <stdlib.h>
+#include <sys/time.h>
+
+typedef unsigned long long cycles_t;
+
+static inline cycles_t get_cycles (void)
+{
+	long long thetime;
+	struct timeval tv;
+
+	if (gettimeofday(&tv, NULL) != 0) {
+		perror("gettimeofday");
+		abort();
+	}
+	thetime = ((long long)tv.tv_sec) * 1000000ULL + ((long long)tv.tv_usec);
+	return (cycles_t)thetime;
+}
+
+#ifdef __cplusplus 
+}
+#endif
+
+#include <urcu/arch_generic.h>
+
+#endif /* _URCU_ARCH_ARMV7_H */
diff --git a/urcu/uatomic_arch_unknown.h b/urcu/uatomic_arch_unknown.h
new file mode 100644
index 0000000..d1cf93e
--- /dev/null
+++ b/urcu/uatomic_arch_unknown.h
@@ -0,0 +1,57 @@
+#ifndef _URCU_ARCH_UATOMIC_ARMV7_H
+#define _URCU_ARCH_UATOMIC_ARMV7_H
+
+/* 
+ * Copyright (c) 1991-1994 by Xerox Corporation.  All rights reserved.
+ * Copyright (c) 1996-1999 by Silicon Graphics.  All rights reserved.
+ * Copyright (c) 1999-2004 Hewlett-Packard Development Company, L.P.
+ * Copyright (c) 2009      Mathieu Desnoyers
+ * Copyright (c) 2010      Paul E. McKenney, IBM Corporation
+ *			   (Adapted from uatomic_arch_ppc.h)
+ *
+ * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
+ * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
+ *
+ * Permission is hereby granted to use or copy this program
+ * for any purpose,  provided the above notices are retained on all copies.
+ * Permission to modify the code and to distribute modified code is granted,
+ * provided the above notices are retained, and a notice that the code was
+ * modified is included with the above copyright notice.
+ *
+ * Code inspired from libuatomic_ops-1.2, inherited in part from the
+ * Boehm-Demers-Weiser conservative garbage collector.
+ */
+
+#include <urcu/compiler.h>
+#include <urcu/system.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif 
+
+#define ILLEGAL_INSTR	".long	0xd00d00" /* @@@FIXME from ppc to ARM. */
+
+/*
+ * Using a isync as second barrier for exchange to provide acquire semantic.
+ * According to uatomic_ops/sysdeps/gcc/powerpc.h, the documentation is "fairly
+ * explicit that this also has acquire semantics."
+ * Derived from AO_compare_and_swap(), but removed the comparison.
+ */
+
+/* xchg */
+#define uatomic_xchg(addr, v)	 __sync_lock_test_and_set(addr, v);
+
+/* cmpxchg */
+#define uatomic_cmpxchg(addr, old, _new) \
+	__sync_val_compare_and_swap(addr, old, _new)
+
+/* uatomic_add_return */
+#define uatomic_add_return(addr, v)  __sync_add_and_fetch(addr, v)
+
+#ifdef __cplusplus 
+}
+#endif
+
+#include <urcu/uatomic_generic.h>
+
+#endif /* _URCU_ARCH_UATOMIC_ARMV7_H */