[PATCH 1/5] Make the system C11 atomics headers fully compatible with external GCC.

[Sebastian Huber <sebastian.huber@embedded-brains.de>]

From: jhb <jhb@FreeBSD.org>

The <sys/cdefs.h> and <stdatomic.h> headers already included support for
C11 atomics via intrinsincs in modern versions of GCC, but these versions
tried to "hide" atomic variables inside a wrapper structure.  This wrapper
is not compatible with GCC's internal <stdatomic.h> header, so that if
GCC's <stdatomic.h> was used together with <sys/cdefs.h>, use of C11
atomics would fail to compile.  Fix this by not hiding atomic variables
in a structure for modern versions of GCC.  The headers already avoid
using a wrapper structure on clang.

Note that this wrapper was only used if C11 was not enabled (e.g.
via -std=c99), so this also fixes compile failures if a modern version
of GCC was used with -std=c11 but with FreeBSD's <stdatomic.h> instead
of GCC's <stdatomic.h> and this change fixes that case as well.

Reported by:	Mark Millard
Reviewed by:	kib
Differential Revision:	https://reviews.freebsd.org/D16585
---
 newlib/libc/include/stdatomic.h | 25 +++++++++++--------------
 newlib/libc/include/sys/cdefs.h |  2 +-
 2 files changed, 12 insertions(+), 15 deletions(-)

diff --git a/newlib/libc/include/stdatomic.h b/newlib/libc/include/stdatomic.h
index 09c0cf73e..1441c9e3b 100644
--- a/newlib/libc/include/stdatomic.h
+++ b/newlib/libc/include/stdatomic.h
@@ -169,12 +169,9 @@ atomic_signal_fence(memory_order __order __unused)
 /* Atomics in kernelspace are always lock-free. */
 #define	atomic_is_lock_free(obj) \
 	((void)(obj), (_Bool)1)
-#elif defined(__CLANG_ATOMICS)
+#elif defined(__CLANG_ATOMICS) || defined(__GNUC_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), &(obj)->__val)
 #else
 #define	atomic_is_lock_free(obj) \
 	((void)(obj), sizeof((obj)->__val) <= sizeof(void *))
@@ -260,28 +257,28 @@ typedef _Atomic(uintmax_t)		atomic_uintmax_t;
 #elif defined(__GNUC_ATOMICS)
 #define	atomic_compare_exchange_strong_explicit(object, expected,	\
     desired, success, failure)						\
-	__atomic_compare_exchange_n(&(object)->__val, expected,		\
+	__atomic_compare_exchange_n(object, expected,			\
 	    desired, 0, success, failure)
 #define	atomic_compare_exchange_weak_explicit(object, expected,		\
     desired, success, failure)						\
-	__atomic_compare_exchange_n(&(object)->__val, expected,		\
+	__atomic_compare_exchange_n(object, expected,			\
 	    desired, 1, success, failure)
 #define	atomic_exchange_explicit(object, desired, order)		\
-	__atomic_exchange_n(&(object)->__val, desired, order)
+	__atomic_exchange_n(object, desired, order)
 #define	atomic_fetch_add_explicit(object, operand, order)		\
-	__atomic_fetch_add(&(object)->__val, operand, order)
+	__atomic_fetch_add(object, operand, order)
 #define	atomic_fetch_and_explicit(object, operand, order)		\
-	__atomic_fetch_and(&(object)->__val, operand, order)
+	__atomic_fetch_and(object, operand, order)
 #define	atomic_fetch_or_explicit(object, operand, order)		\
-	__atomic_fetch_or(&(object)->__val, operand, order)
+	__atomic_fetch_or(object, operand, order)
 #define	atomic_fetch_sub_explicit(object, operand, order)		\
-	__atomic_fetch_sub(&(object)->__val, operand, order)
+	__atomic_fetch_sub(object, operand, order)
 #define	atomic_fetch_xor_explicit(object, operand, order)		\
-	__atomic_fetch_xor(&(object)->__val, operand, order)
+	__atomic_fetch_xor(object, operand, order)
 #define	atomic_load_explicit(object, order)				\
-	__atomic_load_n(&(object)->__val, order)
+	__atomic_load_n(object, order)
 #define	atomic_store_explicit(object, desired, order)			\
-	__atomic_store_n(&(object)->__val, desired, order)
+	__atomic_store_n(object, desired, order)
 #else
 #define	__atomic_apply_stride(object, operand) \
 	(((__typeof__((object)->__val))0) + (operand))
diff --git a/newlib/libc/include/sys/cdefs.h b/newlib/libc/include/sys/cdefs.h
index ccb47ea40..9a0466fff 100644
--- a/newlib/libc/include/sys/cdefs.h
+++ b/newlib/libc/include/sys/cdefs.h
@@ -288,7 +288,7 @@
 #endif
 
 #if !defined(__cplusplus) && !__has_extension(c_atomic) && \
-    !__has_extension(cxx_atomic)
+	!__has_extension(cxx_atomic) && !__GNUC_PREREQ__(4, 7)
 /*
  * No native support for _Atomic(). Place object in structure to prevent
  * most forms of direct non-atomic access.
-- 
2.26.2