[PATCH] atomic: Switch to builtin atomics
Wilco Dijkstra
Wilco.Dijkstra@arm.com
Mon Sep 8 12:56:17 GMT 2025
Switch to standard builtin atomics by removing the defines for !USE_ATOMIC_COMPILER_BUILTINS.
Fix m68k to __HAVE_64B_ATOMICS set to 0.
Passes buildmanyglibc, OK for commit?
---
diff --git a/include/atomic.h b/include/atomic.h
index 44a4ce8d711f3460194b15a1bf2c1bd8f33399a7..dbfaa3f156c3673c46865c36ed915212989e7a8e 100644
--- a/include/atomic.h
+++ b/include/atomic.h
@@ -198,10 +198,6 @@
C11. Usually, a function named atomic_OP_MO(args) is equivalent to C11's
atomic_OP_explicit(args, memory_order_MO); exceptions noted below. */
-/* Each arch can request to use compiler built-ins for C11 atomics. If it
- does, all atomics will be based on these. */
-#if USE_ATOMIC_COMPILER_BUILTINS
-
/* We require 32b atomic operations; some archs also support 64b atomic
operations. */
void __atomic_link_error (void);
@@ -315,167 +311,6 @@ void __atomic_link_error (void);
({ __atomic_check_size((mem)); \
__atomic_fetch_xor ((mem), (operand), __ATOMIC_RELEASE); })
-#else /* !USE_ATOMIC_COMPILER_BUILTINS */
-
-/* By default, we assume that read, write, and full barriers are equivalent
- to acquire, release, and seq_cst barriers. Archs for which this does not
- hold have to provide custom definitions of the fences. */
-# ifndef atomic_thread_fence_acquire
-# define atomic_thread_fence_acquire() atomic_read_barrier ()
-# endif
-# ifndef atomic_thread_fence_release
-# define atomic_thread_fence_release() atomic_write_barrier ()
-# endif
-# ifndef atomic_thread_fence_seq_cst
-# define atomic_thread_fence_seq_cst() atomic_full_barrier ()
-# endif
-
-# ifndef atomic_load_relaxed
-# define atomic_load_relaxed(mem) \
- ({ __typeof ((__typeof (*(mem))) *(mem)) __atg100_val; \
- __asm ("" : "=r" (__atg100_val) : "0" (*(mem))); \
- __atg100_val; })
-# endif
-# ifndef atomic_load_acquire
-# define atomic_load_acquire(mem) \
- ({ __typeof (*(mem)) __atg101_val = atomic_load_relaxed (mem); \
- atomic_thread_fence_acquire (); \
- __atg101_val; })
-# endif
-
-# ifndef atomic_store_relaxed
-/* XXX Use inline asm here? */
-# define atomic_store_relaxed(mem, val) do { *(mem) = (val); } while (0)
-# endif
-# ifndef atomic_store_release
-# define atomic_store_release(mem, val) \
- do { \
- atomic_thread_fence_release (); \
- atomic_store_relaxed ((mem), (val)); \
- } while (0)
-# endif
-
-/* On failure, this CAS has memory_order_relaxed semantics. */
-/* XXX This potentially has one branch more than necessary, but archs
- currently do not define a CAS that returns both the previous value and
- the success flag. */
-# ifndef atomic_compare_exchange_weak_acquire
-# define atomic_compare_exchange_weak_acquire(mem, expected, desired) \
- ({ typeof (*(expected)) __atg102_expected = *(expected); \
- *(expected) = \
- atomic_compare_and_exchange_val_acq ((mem), (desired), *(expected)); \
- *(expected) == __atg102_expected; })
-# endif
-# ifndef atomic_compare_exchange_weak_relaxed
-/* XXX Fall back to CAS with acquire MO because archs do not define a weaker
- CAS. */
-# define atomic_compare_exchange_weak_relaxed(mem, expected, desired) \
- atomic_compare_exchange_weak_acquire ((mem), (expected), (desired))
-# endif
-# ifndef atomic_compare_exchange_weak_release
-# define atomic_compare_exchange_weak_release(mem, expected, desired) \
- ({ typeof (*(expected)) __atg103_expected = *(expected); \
- *(expected) = \
- atomic_compare_and_exchange_val_rel ((mem), (desired), *(expected)); \
- *(expected) == __atg103_expected; })
-# endif
-
-/* XXX Fall back to acquire MO because archs do not define a weaker
- atomic_exchange. */
-# ifndef atomic_exchange_relaxed
-# define atomic_exchange_relaxed(mem, val) \
- atomic_exchange_acq ((mem), (val))
-# endif
-# ifndef atomic_exchange_acquire
-# define atomic_exchange_acquire(mem, val) \
- atomic_exchange_acq ((mem), (val))
-# endif
-# ifndef atomic_exchange_release
-# define atomic_exchange_release(mem, val) \
- atomic_exchange_rel ((mem), (val))
-# endif
-
-# ifndef atomic_fetch_add_acquire
-# define atomic_fetch_add_acquire(mem, operand) \
- atomic_exchange_and_add_acq ((mem), (operand))
-# endif
-# ifndef atomic_fetch_add_relaxed
-/* XXX Fall back to acquire MO because the MO semantics of
- atomic_exchange_and_add are not documented; the generic version falls back
- to atomic_exchange_and_add_acq if atomic_exchange_and_add is not defined,
- and vice versa. */
-# define atomic_fetch_add_relaxed(mem, operand) \
- atomic_fetch_add_acquire ((mem), (operand))
-# endif
-# ifndef atomic_fetch_add_release
-# define atomic_fetch_add_release(mem, operand) \
- atomic_exchange_and_add_rel ((mem), (operand))
-# endif
-# ifndef atomic_fetch_add_acq_rel
-# define atomic_fetch_add_acq_rel(mem, operand) \
- ({ atomic_thread_fence_release (); \
- atomic_exchange_and_add_acq ((mem), (operand)); })
-# endif
-
-/* XXX Fall back to acquire MO because archs do not define a weaker
- atomic_and_val. */
-# ifndef atomic_fetch_and_relaxed
-# define atomic_fetch_and_relaxed(mem, operand) \
- atomic_fetch_and_acquire ((mem), (operand))
-# endif
-/* XXX The default for atomic_and_val has acquire semantics, but this is not
- documented. */
-# ifndef atomic_fetch_and_acquire
-# define atomic_fetch_and_acquire(mem, operand) \
- atomic_and_val ((mem), (operand))
-# endif
-# ifndef atomic_fetch_and_release
-/* XXX This unnecessarily has acquire MO. */
-# define atomic_fetch_and_release(mem, operand) \
- ({ atomic_thread_fence_release (); \
- atomic_and_val ((mem), (operand)); })
-# endif
-
-/* XXX The default for atomic_or_val has acquire semantics, but this is not
- documented. */
-# ifndef atomic_fetch_or_acquire
-# define atomic_fetch_or_acquire(mem, operand) \
- atomic_or_val ((mem), (operand))
-# endif
-/* XXX Fall back to acquire MO because archs do not define a weaker
- atomic_or_val. */
-# ifndef atomic_fetch_or_relaxed
-# define atomic_fetch_or_relaxed(mem, operand) \
- atomic_fetch_or_acquire ((mem), (operand))
-# endif
-/* XXX Contains an unnecessary acquire MO because archs do not define a weaker
- atomic_or_val. */
-# ifndef atomic_fetch_or_release
-# define atomic_fetch_or_release(mem, operand) \
- ({ atomic_thread_fence_release (); \
- atomic_fetch_or_acquire ((mem), (operand)); })
-# endif
-
-# ifndef atomic_fetch_xor_release
-/* Failing the atomic_compare_exchange_weak_release reloads the value in
- __atg104_expected, so we need only do the XOR again and retry. */
-# define atomic_fetch_xor_release(mem, operand) \
- ({ __typeof (mem) __atg104_memp = (mem); \
- __typeof (*(mem)) __atg104_expected = (*__atg104_memp); \
- __typeof (*(mem)) __atg104_desired; \
- __typeof (*(mem)) __atg104_op = (operand); \
- \
- do \
- __atg104_desired = __atg104_expected ^ __atg104_op; \
- while (__glibc_unlikely \
- (atomic_compare_exchange_weak_release ( \
- __atg104_memp, &__atg104_expected, __atg104_desired) \
- == 0)); \
- __atg104_expected; })
-#endif
-
-#endif /* !USE_ATOMIC_COMPILER_BUILTINS */
-
/* This operation does not affect synchronization semantics but can be used
in the body of a spin loop to potentially improve its efficiency. */
#ifndef atomic_spin_nop
diff --git a/sysdeps/m68k/m680x0/m68020/atomic-machine.h b/sysdeps/m68k/m680x0/m68020/atomic-machine.h
index 9d25fbc194182c9f2dc08fad33031a4de5b2c6bf..d586d06d89b85162aaaeb9ec2c5eadde433d6e2c 100644
--- a/sysdeps/m68k/m680x0/m68020/atomic-machine.h
+++ b/sysdeps/m68k/m680x0/m68020/atomic-machine.h
@@ -15,7 +15,7 @@
License along with the GNU C Library. If not, see
<https://www.gnu.org/licenses/>. */
-#define __HAVE_64B_ATOMICS 1
+#define __HAVE_64B_ATOMICS 0
#define USE_ATOMIC_COMPILER_BUILTINS 0
/* XXX Is this actually correct? */
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