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116 lines
3.2 KiB
C
116 lines
3.2 KiB
C
/* Copyright (C) 2012-2024 Free Software Foundation, Inc.
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Contributed by Richard Henderson <rth@redhat.com>.
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This file is part of the GNU Atomic Library (libatomic).
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Libatomic is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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Libatomic is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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more details.
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Under Section 7 of GPL version 3, you are granted additional
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permissions described in the GCC Runtime Library Exception, version
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3.1, as published by the Free Software Foundation.
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You should have received a copy of the GNU General Public License and
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a copy of the GCC Runtime Library Exception along with this program;
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see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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<http://www.gnu.org/licenses/>. */
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#include "libatomic_i.h"
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/* If we support the builtin, just use it. */
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#if !DONE && SIZE(HAVE_ATOMIC_LDST)
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UTYPE
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SIZE(libat_load) (UTYPE *mptr, int smodel)
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{
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if (maybe_specialcase_relaxed(smodel))
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return __atomic_load_n (mptr, __ATOMIC_RELAXED);
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else if (maybe_specialcase_acqrel(smodel))
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/* Note that REL and ACQ_REL are not valid for loads. */
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return __atomic_load_n (mptr, __ATOMIC_ACQUIRE);
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else
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return __atomic_load_n (mptr, __ATOMIC_SEQ_CST);
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}
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#define DONE 1
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#endif /* HAVE_ATOMIC_LOAD */
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/* If we have compare-and-swap, use it to swap 0 with 0 and as a side
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effect load the original value. */
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#if !DONE && defined(atomic_compare_exchange_n)
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UTYPE
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SIZE(libat_load) (UTYPE *mptr, int smodel)
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{
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UTYPE t = 0;
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if (maybe_specialcase_relaxed(smodel))
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atomic_compare_exchange_n (mptr, &t, 0, true,
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__ATOMIC_RELAXED, __ATOMIC_RELAXED);
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else if (maybe_specialcase_acqrel(smodel))
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atomic_compare_exchange_n (mptr, &t, 0, true,
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__ATOMIC_ACQ_REL, __ATOMIC_ACQ_REL);
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else
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atomic_compare_exchange_n (mptr, &t, 0, true,
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__ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);
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return t;
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}
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#define DONE 1
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#endif /* atomic_compare_exchange_n */
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/* Similar, but only assume a word-sized compare-and-swap. */
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#if !DONE && N < WORDSIZE && defined(atomic_compare_exchange_w)
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UTYPE
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SIZE(libat_load) (UTYPE *mptr, int smodel)
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{
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UWORD shift, t, *wptr;
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pre_barrier (smodel);
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wptr = (UWORD *)((uintptr_t)mptr & -WORDSIZE);
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shift = (((uintptr_t)mptr % WORDSIZE) * CHAR_BIT) ^ SIZE(INVERT_MASK);
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/* Exchange 0 with 0, placing the old value of *WPTR in T. */
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t = 0;
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atomic_compare_exchange_w (wptr, &t, 0);
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post_barrier (smodel);
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return t >> shift;
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}
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#define DONE 1
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#endif /* HAVE_ATOMIC_CAS && N < WORDSIZE */
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/* Otherwise, fall back to some sort of protection mechanism. */
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#if !DONE
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UTYPE
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SIZE(libat_load) (UTYPE *mptr, int smodel)
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{
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UTYPE ret;
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UWORD magic;
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pre_seq_barrier (smodel);
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magic = protect_start (mptr);
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ret = *mptr;
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protect_end (mptr, magic);
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post_seq_barrier (smodel);
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return ret;
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}
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#endif
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EXPORT_ALIAS (SIZE(load));
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