From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Tue, 13 Sep 2011 21:00:08 +0000 (-0400)
Subject: urcu-pointer: implement URCU_FORCE_CAST for C++ compatibility of urcu-pointer.h
X-Git-Tag: v0.6.5~23
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=4501f28414425eb594bd1396161a91cb23a11a6f;p=userspace-rcu.git

urcu-pointer: implement URCU_FORCE_CAST for C++ compatibility of urcu-pointer.h

We need to be careful with those, so we do not break aliasing. Our
use-case is to cast back and forth between the same type and a void *
(or void **) type when we pass pointers to C functions. As we cast back
to the same type when the pointer is returned from the function,
aliasing should still work.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---

diff --git a/urcu-pointer.h b/urcu-pointer.h
index 027a18f..67ee381 100644
--- a/urcu-pointer.h
+++ b/urcu-pointer.h
@@ -67,37 +67,40 @@ extern "C" {
 extern void *rcu_dereference_sym(void *p);
 #define rcu_dereference(p)						     \
 	({								     \
-		typeof(p) _________p1 =					     \
-			rcu_dereference_sym((void *)(p));		     \
+		typeof(p) _________p1 =	URCU_FORCE_CAST(typeof(p),	     \
+			rcu_dereference_sym(URCU_FORCE_CAST(void *, p)));    \
 		(_________p1);						     \
 	})
 
 extern void *rcu_cmpxchg_pointer_sym(void **p, void *old, void *_new);
 #define rcu_cmpxchg_pointer(p, old, _new)				     \
 	({								     \
-		typeof(*p) _________pold = (old);			     \
-		typeof(*p) _________pnew = (_new);			     \
-		typeof(*p) _________p1 =				     \
-			rcu_cmpxchg_pointer_sym((void **)(p), _________pold, \
-						_________pnew);		     \
+		typeof(*(p)) _________pold = (old);			     \
+		typeof(*(p)) _________pnew = (_new);			     \
+		typeof(*(p)) _________p1 = URCU_FORCE_CAST(typeof(*(p)),     \
+			rcu_cmpxchg_pointer_sym(URCU_FORCE_CAST(void **, p),\
+						_________pold,		     \
+						_________pnew));	     \
 		(_________p1);						     \
 	})
 
 extern void *rcu_xchg_pointer_sym(void **p, void *v);
 #define rcu_xchg_pointer(p, v)						     \
 	({								     \
-		typeof(*p) _________pv = (v);			             \
-		typeof(*p) _________p1 =				     \
-			rcu_xchg_pointer_sym((void **)(p), _________pv);     \
+		typeof(*(p)) _________pv = (v);			             \
+		typeof(*(p)) _________p1 = URCU_FORCE_CAST(typeof(*(p)),     \
+			rcu_xchg_pointer_sym(URCU_FORCE_CAST(void **, p),    \
+					     _________pv));		     \
 		(_________p1);						     \
 	})
 
 extern void *rcu_set_pointer_sym(void **p, void *v);
 #define rcu_set_pointer(p, v)						     \
 	({								     \
-		typeof(*p) _________pv = (v);			             \
-		typeof(*p) _________p1 =				     \
-			rcu_set_pointer_sym((void **)(p), _________pv);	     \
+		typeof(*(p)) _________pv = (v);			             \
+		typeof(*(p)) _________p1 = URCU_FORCE_CAST(typeof(*(p)),     \
+			rcu_set_pointer_sym(URCU_FORCE_CAST(void **, p),     \
+					    _________pv));		     \
 	})
 
 #endif /* !_LGPL_SOURCE */
diff --git a/urcu/compiler.h b/urcu/compiler.h
index 4bced2a..6db803e 100644
--- a/urcu/compiler.h
+++ b/urcu/compiler.h
@@ -79,4 +79,10 @@
  */
 #define __rcu
 
+#ifdef __cplusplus
+#define URCU_FORCE_CAST(type, arg)	(reinterpret_cast<type>(arg))
+#else
+#define URCU_FORCE_CAST(type, arg)	((type) (arg))
+#endif
+
 #endif /* _URCU_COMPILER_H */