Atomics compatibility wrapper, should work for most recent compilers.

Fallback for x86/amd64 architectures using full barrier.

Change-Id: I80e3beaa721653f760f2d0a6d26a80dd422ab618

Knot.files

@@ -22,6 +22,7 @@ samples/Makefile.am
 src/Makefile.am
 src/common/acl.c
 src/common/acl.h
+src/common/atomic.h
 src/common/base32hex.c
 src/common/base32hex.h
 src/common/base64.c

README

@@ -15,6 +15,10 @@ Optional packages:
 Dependencies for building documentation:
 * texinfo
 
+Knot DNS requires compiler to support atomic intrinsics.
+GCC version at least 4.1 supports legacy atomic builtins, however 4.7 or newer is preferred.
+Clang supports atomics since version 2.9.
+
 Installation
 ============
 

src/Makefile.am

@@ -205,6 +205,7 @@ libknots_la_SOURCES =				\
 	common/libtap/tap.c			\
 	common/libtap/tap.h			\
 	common/libtap/tap_unit.h		\
+	common/atomic.h				\
 	common/mempattern.h			\
 	common/mempattern.c			\
 	common/descriptor.h			\

src/common/atomic.h

+/*  Copyright (C) 2011 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program 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.
+
+    This program 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.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+/*!
+ * \file atomic.h
+ *
+ * \author Marek Vavrusa <marek.vavrusa@nic.cz>
+ *
+ * \brief Compatibility layer for atomic operations.
+ *
+ * Supports both __atomic and __sync legacy code.
+ * Based on the code bits from queue by Rusty Russel <rusty@rustcorp.com.au>.
+ *
+ * \addtogroup common_lib
+ * @{
+ */
+
+#ifndef _KNOTD_ATOMIC_H_
+#define _KNOTD_ATOMIC_H_
+
+#include <stdbool.h>
+#if defined(__ATOMIC_SEQ_CST)  /* GCC4.7+ supports C11 atomics. */
+
+static inline unsigned int read_once(unsigned int *ptr, int memmodel)
+{
+	return __atomic_load_n(ptr, memmodel);
+}
+
+static inline void *read_ptr(void **ptr, int memmodel)
+{
+	return __atomic_load_n(ptr, memmodel);
+}
+
+static inline void store_once(unsigned int *ptr, unsigned int val, int memmodel)
+{
+	__atomic_store_n(ptr, val, memmodel);
+}
+
+static inline void store_ptr(void **ptr, void *val, int memmodel)
+{
+	__atomic_store_n(ptr, val, memmodel);
+}
+
+static inline void atomic_inc(unsigned int *val, int memmodel)
+{
+	__atomic_add_fetch(val, 1, memmodel);
+}
+
+static inline void atomic_dec(unsigned int *val, int memmodel)
+{
+	__atomic_sub_fetch(val, 1, memmodel);
+}
+
+static inline bool compare_and_swap(unsigned int *ptr,
+	                            unsigned int old, unsigned int nval, int memmodel)
+{
+	return __atomic_compare_exchange_n(ptr, &old, nval, false,
+					   memmodel, memmodel);
+}
+
+#else /* Legacy __sync interface */
+
+#if defined(__i386__) || defined(__i686__) || defined(__amd64__)
+static inline void mb(void) /* mfence compatible */
+{
+	asm volatile ("mfence" : : : "memory");
+}
+#else                       /* last resort for other architectures */
+static inline void mb(void)
+{
+	__sync_synchronize();
+}
+#endif
+
+/* Define as full barrier. */
+#undef __ATOMIC_SEQ_CST
+#undef __ATOMIC_RELAXED
+#undef __ATOMIC_ACQUIRE
+#undef __ATOMIC_RELEASE
+#define __ATOMIC_SEQ_CST 1
+#define __ATOMIC_RELAXED 1
+#define __ATOMIC_ACQUIRE 1
+#define __ATOMIC_RELEASE 0
+
+static inline unsigned int read_once(unsigned int *ptr, int memmodel)
+{
+	return __sync_fetch_and_add(ptr, 0);
+}
+
+static inline void *read_ptr(void **ptr, int memmodel)
+{
+	return __sync_fetch_and_add(ptr, 0);
+}
+
+static inline void store_once(unsigned int *ptr, unsigned int val, int memmodel)
+{
+	*(volatile unsigned int *)ptr = val;
+	if (memmodel)
+		mb();
+}
+
+static inline void store_ptr(void **ptr, void *val, int memmodel)
+{
+	*(void * volatile *)ptr = val;
+	if (memmodel)
+		mb();
+}
+
+static inline void atomic_inc(unsigned int *val, int memmodel)
+{
+	__sync_fetch_and_add(val, 1);
+}
+
+static inline void atomic_dec(unsigned int *val, int memmodel)
+{
+	__sync_fetch_and_sub(val, 1);
+}
+
+static inline bool compare_and_swap(unsigned int *ptr,
+                                    unsigned int old, unsigned int nval, int memmodel)
+{
+	return __sync_bool_compare_and_swap(ptr, old, nval);
+}
+
+#endif
+
+#endif /* _KNOTD_ATOMIC_H_ */
+
+/*! @} */

src/common/queue.c

@@ -21,134 +21,13 @@
  * THE SOFTWARE.
  */
 #include "queue.h"
+#include "atomic.h"
 #include "config.h"
 #include <stdbool.h>
 #include <string.h>
 #include <assert.h>
 #include <stdio.h>
 
-#define HAVE_GCC_ATOMICS 1
-#if HAVE_GCC_ATOMICS
-/* Even these will go away with stdatomic.h */
-static unsigned int read_once(unsigned int *ptr, int memmodel)
-{
-	return __atomic_load_n(ptr, memmodel);
-}
-
-static void *read_ptr(void **ptr, int memmodel)
-{
-	return __atomic_load_n(ptr, memmodel);
-}
-
-static void store_once(unsigned int *ptr, unsigned int val, int memmodel)
-{
-	__atomic_store_n(ptr, val, memmodel);
-}
-
-static void store_ptr(void **ptr, void *val, int memmodel)
-{
-	__atomic_store_n(ptr, val, memmodel);
-}
-
-static void atomic_inc(unsigned int *val, int memmodel)
-{
-	__atomic_add_fetch(val, 1, memmodel);
-}
-
-static void atomic_dec(unsigned int *val, int memmodel)
-{
-	__atomic_sub_fetch(val, 1, memmodel);
-}
-
-static bool compare_and_swap(unsigned int *ptr,
-			     unsigned int old, unsigned int new, int memmodel)
-{
-	return __atomic_compare_exchange_n(ptr, &old, new, false,
-					   memmodel, memmodel);
-}
-#else
-#undef __ATOMIC_SEQ_CST
-#undef __ATOMIC_RELAXED
-#undef __ATOMIC_ACQUIRE
-#undef __ATOMIC_RELEASE
-
-/* Overkill, but all-or-nothing keeps it simple. */
-#define __ATOMIC_SEQ_CST 1
-#define __ATOMIC_RELAXED 1
-#define __ATOMIC_ACQUIRE 1
-#define __ATOMIC_RELEASE 0
-
-#ifdef __i386__
-static inline void mb(void)
-{
-	asm volatile ("mfence" : : : "memory");
-}
-#else
-#error implement mb
-#endif
-
-static unsigned int read_once(unsigned int *ptr, bool barrier)
-{
-	if (barrier)
-		mb();
-	return *(volatile unsigned int *)ptr;
-}
-
-static void *read_ptr(void **ptr, bool barrier)
-{
-	if (barrier)
-		mb();
-	return *(void * volatile *)ptr;
-}
-
-static void store_once(unsigned int *ptr, unsigned int val, bool barrier)
-{
-	*(volatile unsigned int *)ptr = val;
-	if (barrier)
-		mb();
-}
-
-static void store_ptr(void **ptr, void *val, bool barrier)
-{
-	*(void * volatile *)ptr = val;
-	if (barrier)
-		mb();
-}
-
-static void atomic_inc(unsigned int *val, bool barrier)
-{
-#ifdef __i386__
-	asm volatile ("lock addl $1, (%0)" : : "r"(val) : "memory");
-#else
-#error implement atomic_inc
-#endif
-}
-
-static void atomic_dec(unsigned int *val, bool barrier)
-{
-#ifdef __i386__
-	asm volatile ("lock subl $1, (%0)" : : "r"(val) : "memory");
-#else
-#error implement atomic_dec
-#endif
-}
-
-static bool compare_and_swap(unsigned int *ptr,
-			     unsigned int old, unsigned int new,
-			     int memmodel)
-{
-#ifdef __i386__
-	unsigned int prev;
-
-	asm volatile ("lock cmpxchgl %1, (%2)"
-		      : "=a"(prev) : "r"(new), "r"(ptr), "a"(old) : "memory");
-	return prev == old;
-#else
-#error implement compare_and_swap
-#endif
-}
-#endif /* ! GCC 4.7 or above */
-
 static void wait_for_change(unsigned int *ptr, unsigned int val)
 {
 	while (read_once(ptr, __ATOMIC_RELAXED) == val);