svn commit: r252413 - head/sys/sys

[Ed Schouten]

Author: ed
Date: Sun Jun 30 10:38:20 2013
New Revision: 252413
URL: http://svnweb.freebsd.org/changeset/base/252413

Log:
  Make atomic_fetch_add() and atomic_fetch_sub() work for pointers with GCC 4.2.
  
  According to the standard, atomic_fetch_*() has to behave identical to
  regular arithmetic. This means that for pointer types, we have to apply
  the stride when doing addition/subtraction.
  
  The GCC documentation seems to imply this is done for __sync_*() as
  well. Unfortunately, both tests and Googling seems to reveal this is not
  really the case. Fix this by performing the multiplication with the
  stride manually.

Modified:
  head/sys/sys/stdatomic.h

Modified: head/sys/sys/stdatomic.h
==============================================================================
--- head/sys/sys/stdatomic.h	Sun Jun 30 08:59:33 2013	(r252412)
+++ head/sys/sys/stdatomic.h	Sun Jun 30 10:38:20 2013	(r252413)
@@ -281,6 +281,8 @@ typedef _Atomic(__uintmax_t)		atomic_uin
 #define	atomic_store_explicit(object, desired, order)			\
 	__atomic_store_n(&(object)->__val, desired, order)
 #else
+#define	__atomic_apply_stride(object, operand) \
+	(((__typeof__((object)->__val))0) + (operand))
 #define	atomic_compare_exchange_strong_explicit(object, expected,	\
     desired, success, failure)	__extension__ ({			\
 	__typeof__(expected) __ep = (expected);				\
@@ -313,13 +315,15 @@ __extension__ ({							\
 })
 #endif
 #define	atomic_fetch_add_explicit(object, operand, order)		\
-	((void)(order), __sync_fetch_and_add(&(object)->__val, operand))
+	((void)(order), __sync_fetch_and_add(&(object)->__val,		\
+	    __atomic_apply_stride(object, operand)))
 #define	atomic_fetch_and_explicit(object, operand, order)		\
 	((void)(order), __sync_fetch_and_and(&(object)->__val, operand))
 #define	atomic_fetch_or_explicit(object, operand, order)		\
 	((void)(order), __sync_fetch_and_or(&(object)->__val, operand))
 #define	atomic_fetch_sub_explicit(object, operand, order)		\
-	((void)(order), __sync_fetch_and_sub(&(object)->__val, operand))
+	((void)(order), __sync_fetch_and_sub(&(object)->__val,		\
+	    __atomic_apply_stride(object, operand)))
 #define	atomic_fetch_xor_explicit(object, operand, order)		\
 	((void)(order), __sync_fetch_and_xor(&(object)->__val, operand))
 #define	atomic_load_explicit(object, order)				\