From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Wed, 8 May 2013 13:53:45 +0000 (-0400)
Subject: Fix: membarrier fallback symbol conflict
X-Git-Tag: v0.8.0~81
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=553b7eb9da3a223368abdf3f6a5ead35acf8a20b;p=userspace-rcu.git

Fix: membarrier fallback symbol conflict

* Lai Jiangshan (laijs@cn.fujitsu.com) wrote:
> Hi, Mathieu,
>
> There is a big compatible problem in URCU which should be fix in next round.
>
> LB: liburcu built on the system which has sys_membarrier().
> LU: liburcu built on the system which does NOT have sys_membarrier().
>
> LBM: liburcu-mb ....
> LUM: liburcu-mb ...
>
> AB: application(-lliburcu) built on the system which has sys_membarrier().
> AU: application(-lliburcu) built on the system which does NOT have
> sys_membarrier().
>
> ABM application(-lliburcu-mb) ...
> AUM application(-lliburcu-mb) ...
>
> AB/AU + LB/LU: 4 combinations
> ABM/AUM + LBM/LUM: 4 combinations
>
> I remember some of the 8 combinations can't works due to symbols are
> miss match.  only LU+AB and LB+AU ?
>
> could you check it?
>
> How to fix it: In LU and AU, keep all the symbol name/ABI as LA and
> AB, but only the behaviors falls back to URCU_MB.

Define membarrier() as -ENOSYS when SYS_membarrier is not found in the
system headers. Check dynamically for membarrier availability to ensure
ABI compatibility between applications and librairies.

Reported-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---

diff --git a/urcu.c b/urcu.c
index b3f94da..1d5c06f 100644
--- a/urcu.c
+++ b/urcu.c
@@ -62,6 +62,24 @@
  */
 #define RCU_QS_ACTIVE_ATTEMPTS 100
 
+/*
+ * RCU_MEMBARRIER is only possibly available on Linux.
+ */
+#if defined(RCU_MEMBARRIER) && defined(__linux__)
+#include <syscall.h>
+#endif
+
+/* If the headers do not support SYS_membarrier, fall back on RCU_MB */
+#ifdef SYS_membarrier
+# define membarrier(...)		syscall(SYS_membarrier, __VA_ARGS__)
+#else
+# define membarrier(...)		-ENOSYS
+#endif
+
+#define MEMBARRIER_EXPEDITED		(1 << 0)
+#define MEMBARRIER_DELAYED		(1 << 1)
+#define MEMBARRIER_QUERY		(1 << 16)
+
 #ifdef RCU_MEMBARRIER
 static int init_done;
 int rcu_has_sys_membarrier;
@@ -139,7 +157,7 @@ static void mutex_unlock(pthread_mutex_t *mutex)
 static void smp_mb_master(int group)
 {
 	if (caa_likely(rcu_has_sys_membarrier))
-		membarrier(MEMBARRIER_EXPEDITED);
+		(void) membarrier(MEMBARRIER_EXPEDITED);
 	else
 		cmm_smp_mb();
 }
diff --git a/urcu/map/urcu.h b/urcu/map/urcu.h
index 217bff5..77b3721 100644
--- a/urcu/map/urcu.h
+++ b/urcu/map/urcu.h
@@ -38,31 +38,6 @@
 #define RCU_MEMBARRIER
 #endif
 
-/*
- * RCU_MEMBARRIER is only possibly available on Linux. Fallback to
- * RCU_MB
- * otherwise.
- */
-#if !defined(__linux__) && defined(RCU_MEMBARRIER)
-#undef RCU_MEMBARRIER
-#define RCU_MB
-#endif
-
-#ifdef RCU_MEMBARRIER
-#include <syscall.h>
-
-/* If the headers do not support SYS_membarrier, statically use RCU_MB */
-#ifdef SYS_membarrier
-# define MEMBARRIER_EXPEDITED		(1 << 0)
-# define MEMBARRIER_DELAYED		(1 << 1)
-# define MEMBARRIER_QUERY		(1 << 16)
-# define membarrier(...)		syscall(SYS_membarrier, __VA_ARGS__)
-#else
-# undef RCU_MEMBARRIER
-# define RCU_MB
-#endif
-#endif
-
 #ifdef RCU_MEMBARRIER
 
 #define rcu_read_lock			rcu_read_lock_memb
diff --git a/urcu/static/urcu.h b/urcu/static/urcu.h
index bee97ee..53d2610 100644
--- a/urcu/static/urcu.h
+++ b/urcu/static/urcu.h
@@ -51,30 +51,6 @@ extern "C" {
 #define RCU_MEMBARRIER
 #endif
 
-/*
- * RCU_MEMBARRIER is only possibly available on Linux. Fallback to RCU_MB
- * otherwise.
- */
-#if !defined(__linux__) && defined(RCU_MEMBARRIER)
-#undef RCU_MEMBARRIER
-#define RCU_MB
-#endif
-
-#ifdef RCU_MEMBARRIER
-#include <syscall.h>
-
-/* If the headers do not support SYS_membarrier, statically use RCU_MB */
-#ifdef SYS_membarrier
-# define MEMBARRIER_EXPEDITED		(1 << 0)
-# define MEMBARRIER_DELAYED		(1 << 1)
-# define MEMBARRIER_QUERY		(1 << 16)
-# define membarrier(...)		syscall(SYS_membarrier, __VA_ARGS__)
-#else
-# undef RCU_MEMBARRIER
-# define RCU_MB
-#endif
-#endif
-
 /*
  * This code section can only be included in LGPL 2.1 compatible source code.
  * See below for the function call wrappers which can be used in code meant to