From 3b6633ba841dc4331a31de78b4713da2e53f94a0 Mon Sep 17 00:00:00 2001
From: Marek Vavrusa <marek.vavrusa@nic.cz>
Date: Thu, 25 Apr 2013 17:06:07 +0200
Subject: [PATCH] Atomics compatibility wrapper, should work for most recent
compilers.
Fallback for x86/amd64 architectures using full barrier.
Change-Id: I80e3beaa721653f760f2d0a6d26a80dd422ab618
---
Knot.files | 1 +
README | 4 ++
src/Makefile.am | 1 +
src/common/atomic.h | 141 ++++++++++++++++++++++++++++++++++++++++++++
src/common/queue.c | 123 +-------------------------------------
5 files changed, 148 insertions(+), 122 deletions(-)
create mode 100644 src/common/atomic.h
diff --git a/Knot.files b/Knot.files
index f9368309d7..a8c1269eb1 100644
--- a/Knot.files
+++ b/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
diff --git a/README b/README
index cc48e48aeb..fdd2172970 100644
--- a/README
+++ b/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
============
diff --git a/src/Makefile.am b/src/Makefile.am
index 72e5bc02bd..e254e961ea 100644
--- a/src/Makefile.am
+++ b/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 \
diff --git a/src/common/atomic.h b/src/common/atomic.h
new file mode 100644
index 0000000000..17cd4e52cf
--- /dev/null
+++ b/src/common/atomic.h
@@ -0,0 +1,141 @@
+/* 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_ */
+
+/*! @} */
diff --git a/src/common/queue.c b/src/common/queue.c
index 753f754eee..182a8ddf3f 100644
--- a/src/common/queue.c
+++ b/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);
--
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