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Make the system C11 atomics headers fully compatible with external GCC.

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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
This commit is contained in:
John Baldwin 2018-08-06 23:51:08 +00:00
parent 1979b51141
commit d2aec9714a
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=337399
2 changed files with 12 additions and 15 deletions
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2
sys/sys/cdefs.h
View File

@ -268,7 +268,7 @@
#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.

25
sys/sys/stdatomic.h
View File

@ -171,12 +171,9 @@ 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))