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7adcbafe | 1 | /* Copyright (C) 2012-2022 Free Software Foundation, Inc. |
48310492 RH |
2 | Contributed by Richard Henderson <rth@redhat.com>. |
3 | ||
4 | This file is part of the GNU Atomic Library (libatomic). | |
5 | ||
6 | Libatomic 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 of the License, or | |
9 | (at your option) any later version. | |
10 | ||
11 | Libatomic 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 | #include "libatomic_i.h" | |
26 | ||
27 | ||
28 | /* If we support the builtin, just use it. */ | |
29 | #if !DONE && SIZE(HAVE_ATOMIC_LDST) | |
30 | UTYPE | |
31 | SIZE(libat_load) (UTYPE *mptr, int smodel) | |
32 | { | |
33 | if (maybe_specialcase_relaxed(smodel)) | |
34 | return __atomic_load_n (mptr, __ATOMIC_RELAXED); | |
35 | else if (maybe_specialcase_acqrel(smodel)) | |
36 | /* Note that REL and ACQ_REL are not valid for loads. */ | |
37 | return __atomic_load_n (mptr, __ATOMIC_ACQUIRE); | |
38 | else | |
39 | return __atomic_load_n (mptr, __ATOMIC_SEQ_CST); | |
40 | } | |
41 | ||
42 | #define DONE 1 | |
43 | #endif /* HAVE_ATOMIC_LOAD */ | |
44 | ||
45 | ||
46 | /* If we have compare-and-swap, use it to swap 0 with 0 and as a side | |
47 | effect load the original value. */ | |
48 | #if !DONE && defined(atomic_compare_exchange_n) | |
49 | UTYPE | |
50 | SIZE(libat_load) (UTYPE *mptr, int smodel) | |
51 | { | |
52 | UTYPE t = 0; | |
53 | ||
54 | if (maybe_specialcase_relaxed(smodel)) | |
55 | atomic_compare_exchange_n (mptr, &t, 0, true, | |
56 | __ATOMIC_RELAXED, __ATOMIC_RELAXED); | |
57 | else if (maybe_specialcase_acqrel(smodel)) | |
58 | atomic_compare_exchange_n (mptr, &t, 0, true, | |
59 | __ATOMIC_ACQ_REL, __ATOMIC_ACQ_REL); | |
60 | else | |
61 | atomic_compare_exchange_n (mptr, &t, 0, true, | |
62 | __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST); | |
63 | ||
64 | return t; | |
65 | } | |
66 | ||
67 | #define DONE 1 | |
68 | #endif /* atomic_compare_exchange_n */ | |
69 | ||
70 | ||
71 | /* Similar, but only assume a word-sized compare-and-swap. */ | |
72 | #if !DONE && N < WORDSIZE && defined(atomic_compare_exchange_w) | |
73 | UTYPE | |
74 | SIZE(libat_load) (UTYPE *mptr, int smodel) | |
75 | { | |
76 | UWORD shift, t, *wptr; | |
77 | ||
78 | pre_barrier (smodel); | |
79 | ||
80 | wptr = (UWORD *)((uintptr_t)mptr & -WORDSIZE); | |
81 | shift = (((uintptr_t)mptr % WORDSIZE) * CHAR_BIT) ^ SIZE(INVERT_MASK); | |
82 | ||
83 | /* Exchange 0 with 0, placing the old value of *WPTR in T. */ | |
84 | t = 0; | |
85 | atomic_compare_exchange_w (wptr, &t, 0); | |
86 | ||
87 | post_barrier (smodel); | |
88 | return t >> shift; | |
89 | } | |
90 | ||
91 | #define DONE 1 | |
92 | #endif /* HAVE_ATOMIC_CAS && N < WORDSIZE */ | |
93 | ||
94 | ||
95 | /* Otherwise, fall back to some sort of protection mechanism. */ | |
96 | #if !DONE | |
97 | UTYPE | |
98 | SIZE(libat_load) (UTYPE *mptr, int smodel) | |
99 | { | |
100 | UTYPE ret; | |
101 | UWORD magic; | |
102 | ||
103 | pre_seq_barrier (smodel); | |
104 | magic = protect_start (mptr); | |
105 | ||
106 | ret = *mptr; | |
107 | ||
108 | protect_end (mptr, magic); | |
109 | post_seq_barrier (smodel); | |
110 | ||
111 | return ret; | |
112 | } | |
113 | #endif | |
114 | ||
115 | EXPORT_ALIAS (SIZE(load)); |