1 /* Copyright (C) 2008-2013 Free Software Foundation, Inc.
2    Contributed by Jakub Jelinek <jakub@redhat.com>.
3 
4    This file is part of the GNU OpenMP Library (libgomp).
5 
6    Libgomp is free software; you can redistribute it and/or modify it
7    under the terms of the GNU General Public License as published by
8    the Free Software Foundation; either version 3, or (at your option)
9    any later version.
10 
11    Libgomp is distributed in the hope that it will be useful, but WITHOUT ANY
12    WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
13    FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
14    more details.
15 
16    Under Section 7 of GPL version 3, you are granted additional
17    permissions described in the GCC Runtime Library Exception, version
18    3.1, as published by the Free Software Foundation.
19 
20    You should have received a copy of the GNU General Public License and
21    a copy of the GCC Runtime Library Exception along with this program;
22    see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
23    <http://www.gnu.org/licenses/>.  */
24 
25 /* This is a Linux specific implementation of a mutex synchronization
26    mechanism for libgomp.  This type is private to the library.  This
27    implementation uses atomic instructions and the futex syscall.  */
28 
29 #include <endian.h>
30 #include <limits.h>
31 #include "wait.h"
32 
33 void *
gomp_ptrlock_get_slow(gomp_ptrlock_t * ptrlock)34 gomp_ptrlock_get_slow (gomp_ptrlock_t *ptrlock)
35 {
36   int *intptr;
37   uintptr_t oldval = 1;
38 
39   __atomic_compare_exchange_n (ptrlock, &oldval, 2, false,
40 			       MEMMODEL_RELAXED, MEMMODEL_RELAXED);
41 
42   /* futex works on ints, not pointers.
43      But a valid work share pointer will be at least
44      8 byte aligned, so it is safe to assume the low
45      32-bits of the pointer won't contain values 1 or 2.  */
46   __asm volatile ("" : "=r" (intptr) : "0" (ptrlock));
47 #if __BYTE_ORDER == __BIG_ENDIAN
48   if (sizeof (*ptrlock) > sizeof (int))
49     intptr += (sizeof (*ptrlock) / sizeof (int)) - 1;
50 #endif
51   do
52     do_wait (intptr, 2);
53   while (__atomic_load_n (intptr, MEMMODEL_RELAXED) == 2);
54   __asm volatile ("" : : : "memory");
55   return (void *) __atomic_load_n (ptrlock, MEMMODEL_ACQUIRE);
56 }
57 
58 void
gomp_ptrlock_set_slow(gomp_ptrlock_t * ptrlock)59 gomp_ptrlock_set_slow (gomp_ptrlock_t *ptrlock)
60 {
61   int *intptr;
62 
63   __asm volatile ("" : "=r" (intptr) : "0" (ptrlock));
64 #if __BYTE_ORDER == __BIG_ENDIAN
65   if (sizeof (*ptrlock) > sizeof (int))
66     intptr += (sizeof (*ptrlock) / sizeof (int)) - 1;
67 #endif
68   futex_wake (intptr, INT_MAX);
69 }
70