11fb784ac5
On nvptx (using a Quadro K2000 with driver 470.103.01) I ran into this:
...
FAIL: gcc.dg/atomic/stdatomic-flag-2.c -O1 execution test
...
which mimimized to:
...
#include <stdatomic.h>
atomic_flag a = ATOMIC_FLAG_INIT;
int main () {
if ((atomic_flag_test_and_set) (&a))
__builtin_abort ();
return 0;
}
...
The atomic_flag_test_and_set is implemented using __atomic_test_and_set_1,
which corresponds to the "word-sized compare-and-swap loop" version of
libat_test_and_set in libatomic/tas_n.c.
The semantics of a test-and-set is that the return value is "true if and only
if the previous contents were 'set'".
But the code uses:
...
return woldval != 0;
...
which means it doesn't look only at the byte that was either set or not set,
but at the entire word.
Fix this by using instead:
...
return (woldval & ((UTYPE) ~(UTYPE) 0 << shift)) != 0;
...
Tested on nvptx.
libatomic/ChangeLog:
2022-03-24 Tom de Vries <tdevries@suse.de>
PR target/105011
* tas_n.c (libat_test_and_set): Fix return value.
116 lines
3.0 KiB
C
116 lines
3.0 KiB
C
/* Copyright (C) 2012-2022 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_TAS)
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bool
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SIZE(libat_test_and_set) (UTYPE *mptr, int smodel)
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{
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if (maybe_specialcase_relaxed(smodel))
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return __atomic_test_and_set (mptr, __ATOMIC_RELAXED);
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else if (maybe_specialcase_acqrel(smodel))
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return __atomic_test_and_set (mptr, __ATOMIC_ACQ_REL);
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else
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return __atomic_test_and_set (mptr, __ATOMIC_SEQ_CST);
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}
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#define DONE 1
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#endif /* HAVE_ATOMIC_TAS */
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/* If this type is smaller than word-sized, fall back to a word-sized
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compare-and-swap loop. */
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#if !DONE && N <= WORDSIZE && defined(atomic_compare_exchange_w)
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bool
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SIZE(libat_test_and_set) (UTYPE *mptr, int smodel)
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{
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UWORD wval, woldval, shift, *wptr, t;
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pre_barrier (smodel);
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if (N < WORDSIZE)
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{
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wptr = (UWORD *)((uintptr_t)mptr & -WORDSIZE);
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shift = SIZE(INVERT_MASK);
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}
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else
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{
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wptr = (UWORD *)mptr;
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shift = 0;
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}
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wval = (UWORD)__GCC_ATOMIC_TEST_AND_SET_TRUEVAL << shift;
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woldval = __atomic_load_n (wptr, __ATOMIC_RELAXED);
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do
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{
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t = woldval | wval;
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}
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while (!atomic_compare_exchange_w (wptr, &woldval, t, true,
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__ATOMIC_RELAXED, __ATOMIC_RELAXED));
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post_barrier (smodel);
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return (woldval & ((UTYPE) ~(UTYPE) 0 << shift)) != 0;
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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 && N == 1
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bool
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SIZE(libat_test_and_set) (UTYPE *mptr, int smodel)
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{
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UTYPE oldval;
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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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oldval = *mptr;
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*mptr = __GCC_ATOMIC_TEST_AND_SET_TRUEVAL;
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protect_end (mptr, magic);
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post_seq_barrier (smodel);
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return oldval != 0;
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}
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#define DONE 1
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#endif /* N == 1 */
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#if !DONE
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bool
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SIZE(libat_test_and_set) (UTYPE *mptr, int smodel UNUSED)
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{
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return libat_test_and_set_1 ((U_1 *)mptr, smodel);
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}
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#endif
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EXPORT_ALIAS (SIZE(test_and_set));
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