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3dd2cbfa35
commit 7fec8a5de6
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date: Thu Nov 13 14:26:08 2025 -0300
Revert __HAVE_64B_ATOMICS configure check
uses 64-bit atomic operations on sem_t if 64-bit atomics are supported.
But sem_t may be aligned to 32-bit on 32-bit architectures.
1. Add a macro, SEM_T_ALIGN, for sem_t alignment.
2. Add a macro, HAVE_UNALIGNED_64B_ATOMICS. Define it if unaligned 64-bit
atomic operations are supported.
3. Add a macro, USE_64B_ATOMICS_ON_SEM_T. Define to 1 if 64-bit atomic
operations are supported and SEM_T_ALIGN is at least 8-byte aligned or
HAVE_UNALIGNED_64B_ATOMICS is defined.
4. Assert that size and alignment of sem_t are not lower than those of
the internal struct new_sem.
5. Check USE_64B_ATOMICS_ON_SEM_T, instead of USE_64B_ATOMICS, when using
64-bit atomic operations on sem_t.
This fixes BZ #33632.
Reviewed-by: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
56 lines
1.6 KiB
C
56 lines
1.6 KiB
C
/* Lock a semaphore if it does not require blocking. Generic version.
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Copyright (C) 2005-2025 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <semaphore.h>
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#include <errno.h>
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#include <pt-internal.h>
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int
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__sem_waitfast (struct new_sem *isem, int definitive_result)
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{
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#if USE_64B_ATOMICS_ON_SEM_T
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uint64_t d = atomic_load_relaxed (&isem->data);
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do
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{
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if ((d & SEM_VALUE_MASK) == 0)
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break;
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if (atomic_compare_exchange_weak_acquire (&isem->data, &d, d - 1))
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/* Successful down. */
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return 0;
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}
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while (definitive_result);
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return -1;
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#else
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unsigned v = atomic_load_relaxed (&isem->value);
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do
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{
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if ((v >> SEM_VALUE_SHIFT) == 0)
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break;
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if (atomic_compare_exchange_weak_acquire (&isem->value,
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&v, v - (1 << SEM_VALUE_SHIFT)))
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/* Successful down. */
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return 0;
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}
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while (definitive_result);
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return -1;
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#endif
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}
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