[PATCH] Update cdefs.h and stdatomic.h

[Sebastian Huber <sebastian dot huber at embedded-brains dot de>]

I recently encountered a problem with the atomic flags implementation
provided by Newlibs <stdatomic.h> (which I copied in March 2013 from
FreeBSD).  I falsely blamed GCC in the first place:

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58259

This patch updates the cdefs.h and stdatomic.h files with the latest
FreeBSD versions which fix the bug:

http://svnweb.freebsd.org/base/head/sys/sys/cdefs.h?revision=251804&view=markup

http://svnweb.freebsd.org/base/head/sys/sys/stdatomic.h?revision=254497&view=markup

newlib/ChangeLog
2013-08-29  Sebastian Huber <sebastian.huber@embedded-brains.de>

	* libc/include/sys/cdefs.h: Synchronize with latest FreeBSD
	version.
	* libc/include/stdatomic.h: Likewise.
---
 newlib/libc/include/stdatomic.h |  193 +++++++++++++++++++++++++++-----------
 newlib/libc/include/sys/cdefs.h |   86 +++++++++++++-----
 2 files changed, 199 insertions(+), 80 deletions(-)

diff --git a/newlib/libc/include/stdatomic.h b/newlib/libc/include/stdatomic.h
index c962cac..09c0cf7 100644
--- a/newlib/libc/include/stdatomic.h
+++ b/newlib/libc/include/stdatomic.h
@@ -33,16 +33,49 @@
 #include <sys/cdefs.h>
 #include <sys/_types.h>
 
-#if __has_feature(cxx_atomic)
+#if __has_extension(c_atomic) || __has_extension(cxx_atomic)
 #define	__CLANG_ATOMICS
 #elif __GNUC_PREREQ__(4, 7)
 #define	__GNUC_ATOMICS
-#elif !defined(__GNUC__)
+#elif defined(__GNUC__)
+#define	__SYNC_ATOMICS
+#else
 #error "stdatomic.h does not support your compiler"
 #endif
 
-#if !defined(__CLANG_ATOMICS)
-#define	_Atomic(T)			struct { volatile T __val; }
+/*
+ * 7.17.1 Atomic lock-free macros.
+ */
+
+#ifdef __GCC_ATOMIC_BOOL_LOCK_FREE
+#define	ATOMIC_BOOL_LOCK_FREE		__GCC_ATOMIC_BOOL_LOCK_FREE
+#endif
+#ifdef __GCC_ATOMIC_CHAR_LOCK_FREE
+#define	ATOMIC_CHAR_LOCK_FREE		__GCC_ATOMIC_CHAR_LOCK_FREE
+#endif
+#ifdef __GCC_ATOMIC_CHAR16_T_LOCK_FREE
+#define	ATOMIC_CHAR16_T_LOCK_FREE	__GCC_ATOMIC_CHAR16_T_LOCK_FREE
+#endif
+#ifdef __GCC_ATOMIC_CHAR32_T_LOCK_FREE
+#define	ATOMIC_CHAR32_T_LOCK_FREE	__GCC_ATOMIC_CHAR32_T_LOCK_FREE
+#endif
+#ifdef __GCC_ATOMIC_WCHAR_T_LOCK_FREE
+#define	ATOMIC_WCHAR_T_LOCK_FREE	__GCC_ATOMIC_WCHAR_T_LOCK_FREE
+#endif
+#ifdef __GCC_ATOMIC_SHORT_LOCK_FREE
+#define	ATOMIC_SHORT_LOCK_FREE		__GCC_ATOMIC_SHORT_LOCK_FREE
+#endif
+#ifdef __GCC_ATOMIC_INT_LOCK_FREE
+#define	ATOMIC_INT_LOCK_FREE		__GCC_ATOMIC_INT_LOCK_FREE
+#endif
+#ifdef __GCC_ATOMIC_LONG_LOCK_FREE
+#define	ATOMIC_LONG_LOCK_FREE		__GCC_ATOMIC_LONG_LOCK_FREE
+#endif
+#ifdef __GCC_ATOMIC_LLONG_LOCK_FREE
+#define	ATOMIC_LLONG_LOCK_FREE		__GCC_ATOMIC_LLONG_LOCK_FREE
+#endif
+#ifdef __GCC_ATOMIC_POINTER_LOCK_FREE
+#define	ATOMIC_POINTER_LOCK_FREE	__GCC_ATOMIC_POINTER_LOCK_FREE
 #endif
 
 /*
@@ -54,9 +87,7 @@
 #define	atomic_init(obj, value)		__c11_atomic_init(obj, value)
 #else
 #define	ATOMIC_VAR_INIT(value)		{ .__val = (value) }
-#define	atomic_init(obj, value) do {					\
-	(obj)->__val = (value);						\
-} while (0)
+#define	atomic_init(obj, value)		((void)((obj)->__val = (value)))
 #endif
 
 /*
@@ -91,43 +122,62 @@
  * atomic operations.
  */
 
-enum memory_order {
+typedef enum {
 	memory_order_relaxed = __ATOMIC_RELAXED,
 	memory_order_consume = __ATOMIC_CONSUME,
 	memory_order_acquire = __ATOMIC_ACQUIRE,
 	memory_order_release = __ATOMIC_RELEASE,
 	memory_order_acq_rel = __ATOMIC_ACQ_REL,
 	memory_order_seq_cst = __ATOMIC_SEQ_CST
-};
+} memory_order;
 
 /*
  * 7.17.4 Fences.
  */
 
+static __inline void
+atomic_thread_fence(memory_order __order __unused)
+{
+
 #ifdef __CLANG_ATOMICS
-#define	atomic_thread_fence(order)	__c11_atomic_thread_fence(order)
-#define	atomic_signal_fence(order)	__c11_atomic_signal_fence(order)
+	__c11_atomic_thread_fence(__order);
 #elif defined(__GNUC_ATOMICS)
-#define	atomic_thread_fence(order)	__atomic_thread_fence(order)
-#define	atomic_signal_fence(order)	__atomic_signal_fence(order)
+	__atomic_thread_fence(__order);
 #else
-#define	atomic_thread_fence(order)	__sync_synchronize()
-#define	atomic_signal_fence(order)	__asm volatile ("" : : : "memory")
+	__sync_synchronize();
 #endif
+}
+
+static __inline void
+atomic_signal_fence(memory_order __order __unused)
+{
+
+#ifdef __CLANG_ATOMICS
+	__c11_atomic_signal_fence(__order);
+#elif defined(__GNUC_ATOMICS)
+	__atomic_signal_fence(__order);
+#else
+	__asm volatile ("" ::: "memory");
+#endif
+}
 
 /*
  * 7.17.5 Lock-free property.
  */
 
-#if defined(__CLANG_ATOMICS)
+#if defined(_KERNEL)
+/* Atomics in kernelspace are always lock-free. */
 #define	atomic_is_lock_free(obj) \
-	__c11_atomic_is_lock_free(sizeof(obj))
+	((void)(obj), (_Bool)1)
+#elif defined(__CLANG_ATOMICS)
+#define	atomic_is_lock_free(obj) \
+	__atomic_is_lock_free(sizeof(*(obj)), obj)
 #elif defined(__GNUC_ATOMICS)
 #define	atomic_is_lock_free(obj) \
-	__atomic_is_lock_free(sizeof((obj)->__val))
+	__atomic_is_lock_free(sizeof((obj)->__val), &(obj)->__val)
 #else
 #define	atomic_is_lock_free(obj) \
-	(sizeof((obj)->__val) <= sizeof(void *))
+	((void)(obj), sizeof((obj)->__val) <= sizeof(void *))
 #endif
 
 /*
@@ -233,61 +283,65 @@ typedef _Atomic(uintmax_t)		atomic_uintmax_t;
 #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) ({					\
-	__typeof__((object)->__val) __v;				\
-	_Bool __r;							\
-	__v = __sync_val_compare_and_swap(&(object)->__val,		\
-	    *(expected), desired);					\
-	__r = *(expected) == __v;					\
-	*(expected) = __v;						\
-	__r;								\
+    desired, success, failure)	__extension__ ({			\
+	__typeof__(expected) __ep = (expected);				\
+	__typeof__(*__ep) __e = *__ep;					\
+	(void)(success); (void)(failure);				\
+	(_Bool)((*__ep = __sync_val_compare_and_swap(&(object)->__val,	\
+	    __e, desired)) == __e);					\
 })
-
 #define	atomic_compare_exchange_weak_explicit(object, expected,		\
     desired, success, failure)						\
 	atomic_compare_exchange_strong_explicit(object, expected,	\
 		desired, success, failure)
 #if __has_builtin(__sync_swap)
 /* Clang provides a full-barrier atomic exchange - use it if available. */
-#define atomic_exchange_explicit(object, desired, order)		\
-	__sync_swap(&(object)->__val, desired)
+#define	atomic_exchange_explicit(object, desired, order)		\
+	((void)(order), __sync_swap(&(object)->__val, desired))
 #else
 /*
  * __sync_lock_test_and_set() is only an acquire barrier in theory (although in
- * practice it is usually a full barrier) so we need an explicit barrier after
+ * practice it is usually a full barrier) so we need an explicit barrier before
  * it.
  */
-#define	atomic_exchange_explicit(object, desired, order) ({		\
-	__typeof__((object)->__val) __v;				\
-	__v = __sync_lock_test_and_set(&(object)->__val, desired);	\
+#define	atomic_exchange_explicit(object, desired, order)		\
+__extension__ ({							\
+	__typeof__(object) __o = (object);				\
+	__typeof__(desired) __d = (desired);				\
+	(void)(order);							\
 	__sync_synchronize();						\
-	__v;								\
+	__sync_lock_test_and_set(&(__o)->__val, __d);			\
 })
 #endif
 #define	atomic_fetch_add_explicit(object, operand, 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)		\
-	__sync_fetch_and_and(&(object)->__val, operand)
+	((void)(order), __sync_fetch_and_and(&(object)->__val, operand))
 #define	atomic_fetch_or_explicit(object, operand, order)		\
-	__sync_fetch_and_or(&(object)->__val, operand)
+	((void)(order), __sync_fetch_and_or(&(object)->__val, operand))
 #define	atomic_fetch_sub_explicit(object, operand, 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)		\
-	__sync_fetch_and_xor(&(object)->__val, operand)
+	((void)(order), __sync_fetch_and_xor(&(object)->__val, operand))
 #define	atomic_load_explicit(object, order)				\
-	__sync_fetch_and_add(&(object)->__val, 0)
-#define	atomic_store_explicit(object, desired, order) do {		\
-	__sync_synchronize();						\
-	(object)->__val = (desired);					\
-	__sync_synchronize();						\
-} while (0)
+	((void)(order), __sync_fetch_and_add(&(object)->__val, 0))
+#define	atomic_store_explicit(object, desired, order)			\
+	((void)atomic_exchange_explicit(object, desired, order))
 #endif
 
 /*
  * Convenience functions.
+ *
+ * Don't provide these in kernel space. In kernel space, we should be
+ * disciplined enough to always provide explicit barriers.
  */
 
+#ifndef _KERNEL
 #define	atomic_compare_exchange_strong(object, expected, desired)	\
 	atomic_compare_exchange_strong_explicit(object, expected,	\
 	    desired, memory_order_seq_cst, memory_order_seq_cst)
@@ -310,23 +364,50 @@ typedef _Atomic(uintmax_t)		atomic_uintmax_t;
 	atomic_load_explicit(object, memory_order_seq_cst)
 #define	atomic_store(object, desired)					\
 	atomic_store_explicit(object, desired, memory_order_seq_cst)
+#endif /* !_KERNEL */
 
 /*
  * 7.17.8 Atomic flag type and operations.
+ *
+ * XXX: Assume atomic_bool can be used as an atomic_flag. Is there some
+ * kind of compiler built-in type we could use?
  */
 
-typedef atomic_bool			atomic_flag;
+typedef struct {
+	atomic_bool	__flag;
+} atomic_flag;
+
+#define	ATOMIC_FLAG_INIT		{ ATOMIC_VAR_INIT(0) }
+
+static __inline _Bool
+atomic_flag_test_and_set_explicit(volatile atomic_flag *__object,
+    memory_order __order)
+{
+	return (atomic_exchange_explicit(&__object->__flag, 1, __order));
+}
+
+static __inline void
+atomic_flag_clear_explicit(volatile atomic_flag *__object, memory_order __order)
+{
+
+	atomic_store_explicit(&__object->__flag, 0, __order);
+}
+
+#ifndef _KERNEL
+static __inline _Bool
+atomic_flag_test_and_set(volatile atomic_flag *__object)
+{
 
-#define	ATOMIC_FLAG_INIT		ATOMIC_VAR_INIT(0)
+	return (atomic_flag_test_and_set_explicit(__object,
+	    memory_order_seq_cst));
+}
 
-#define	atomic_flag_clear_explicit(object, order)			\
-	atomic_store_explicit(object, 0, order)
-#define	atomic_flag_test_and_set_explicit(object, order)		\
-	atomic_compare_exchange_strong_explicit(object, 0, 1, order, order)
+static __inline void
+atomic_flag_clear(volatile atomic_flag *__object)
+{
 
-#define	atomic_flag_clear(object)					\
-	atomic_flag_clear_explicit(object, memory_order_seq_cst)
-#define	atomic_flag_test_and_set(object)				\
-	atomic_flag_test_and_set_explicit(object, memory_order_seq_cst)
+	atomic_flag_clear_explicit(__object, memory_order_seq_cst);
+}
+#endif /* !_KERNEL */
 
 #endif /* !_STDATOMIC_H_ */
diff --git a/newlib/libc/include/sys/cdefs.h b/newlib/libc/include/sys/cdefs.h
index 0aeb3dd..3861683 100644
--- a/newlib/libc/include/sys/cdefs.h
+++ b/newlib/libc/include/sys/cdefs.h
@@ -66,6 +66,23 @@
 # define __ptrvalue     /* nothing */
 #endif
 
+/*
+ * Testing against Clang-specific extensions.
+ */
+
+#ifndef	__has_extension
+#define	__has_extension		__has_feature
+#endif
+#ifndef	__has_feature
+#define	__has_feature(x)	0
+#endif
+#ifndef	__has_include
+#define	__has_include(x)	0
+#endif
+#ifndef	__has_builtin
+#define	__has_builtin(x)	0
+#endif
+
 #if defined(__cplusplus)
 #define	__BEGIN_DECLS	extern "C" {
 #define	__END_DECLS	}
@@ -252,23 +269,45 @@
 /*
  * Keywords added in C11.
  */
-#if defined(__cplusplus) && __cplusplus >= 201103L
-#define	_Alignas(e)		alignas(e)
-#define	_Alignof(e)		alignof(e)
-#define	_Noreturn		[[noreturn]]
-#define	_Static_assert(e, s)	static_assert(e, s)
-/* FIXME: change this to thread_local when clang in base supports it */
-#define	_Thread_local		__thread
-#elif defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L
-/* Do nothing.  They are language keywords. */
+
+#if !defined(__STDC_VERSION__) || __STDC_VERSION__ < 201112L
+
+#if !__has_extension(c_alignas)
+#if (defined(__cplusplus) && __cplusplus >= 201103L) || \
+    __has_extension(cxx_alignas)
+#define	_Alignas(x)		alignas(x)
 #else
-/* Not supported.  Implement them using our versions. */
+/* XXX: Only emulates _Alignas(constant-expression); not _Alignas(type-name). */
 #define	_Alignas(x)		__aligned(x)
+#endif
+#endif
+
+#if defined(__cplusplus) && __cplusplus >= 201103L
+#define	_Alignof(x)		alignof(x)
+#else
 #define	_Alignof(x)		__alignof(x)
+#endif
+
+#if !__has_extension(c_atomic) && !__has_extension(cxx_atomic)
+/*
+ * No native support for _Atomic(). Place object in structure to prevent
+ * most forms of direct non-atomic access.
+ */
+#define	_Atomic(T)		struct { T volatile __val; }
+#endif
+
+#if defined(__cplusplus) && __cplusplus >= 201103L
+#define	_Noreturn		[[noreturn]]
+#else
 #define	_Noreturn		__dead2
-#define	_Thread_local		__thread
+#endif
+
 #if __GNUC_PREREQ__(4, 6) && !defined(__cplusplus)
 /*  Do nothing: _Static_assert() works as per C11 */
+#elif !__has_extension(c_static_assert)
+#if (defined(__cplusplus) && __cplusplus >= 201103L) || \
+    __has_extension(cxx_static_assert)
+#define	_Static_assert(x, y)	static_assert(x, y)
 #elif defined(__COUNTER__)
 #define	_Static_assert(x, y)	__Static_assert(x, __COUNTER__)
 #define	__Static_assert(x, y)	___Static_assert(x, y)
@@ -278,6 +317,18 @@
 #endif
 #endif
 
+#if !__has_extension(c_thread_local)
+/* XXX: Change this to test against C++11 when clang in base supports it. */
+#if /* (defined(__cplusplus) && __cplusplus >= 201103L) || */ \
+    __has_extension(cxx_thread_local)
+#define	_Thread_local		thread_local
+#else
+#define	_Thread_local		__thread
+#endif
+#endif
+
+#endif /* __STDC_VERSION__ || __STDC_VERSION__ < 201112L */
+
 /*
  * Emulation of C11 _Generic().  Unlike the previously defined C11
  * keywords, it is not possible to implement this using exactly the same
@@ -650,17 +701,4 @@
 #endif
 #endif
 
-#ifndef	__has_extension
-#define	__has_extension  __has_feature
-#endif
-#ifndef	__has_feature
-#define	__has_feature(x) 0
-#endif
-#ifndef	__has_include
-#define	__has_include(x) 0
-#endif
-#ifndef	__has_builtin
-#define	__has_builtin(x) 0
-#endif
-
 #endif /* !_SYS_CDEFS_H_ */
-- 
1.7.7