1 // Copyright (C) 2011 The Android Open Source Project
2 // All rights reserved.
3 //
4 // Redistribution and use in source and binary forms, with or without
5 // modification, are permitted provided that the following conditions
6 // are met:
7 // 1. Redistributions of source code must retain the above copyright
8 // notice, this list of conditions and the following disclaimer.
9 // 2. Redistributions in binary form must reproduce the above copyright
10 // notice, this list of conditions and the following disclaimer in the
11 // documentation and/or other materials provided with the distribution.
12 // 3. Neither the name of the project nor the names of its contributors
13 // may be used to endorse or promote products derived from this software
14 // without specific prior written permission.
15 //
16 // THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
17 // ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 // ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
20 // FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 // DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 // OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 // HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 // LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 // OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 // SUCH DAMAGE.
27 //
28 // One-time construction C++ runtime support
29 // See "3.3.2 One-time Construction API" of the Itanium C++ ABI reference
30 // And "3.2.3 Guard variables and the one-time construction API" in the ARM C++ ABI reference.
31
32 /* Note that the ARM C++ ABI defines the size of each guard variable
33 * as 32-bit, while the generic/Itanium one defines it as 64-bit.
34 *
35 * Also the ARM C++ ABI uses the least-significant bit to indicate
36 * completion, while the generic/Itanium one uses the least-significant
37 * byte. In all cases the corresponding item is set to value '1'
38 *
39 * We will treat guard variables here as 32-bit values, even on x86,
40 * given that this representation is compatible with compiler-generated
41 * variables that are 64-bits on little-endian systems. This makes the
42 * code simpler and slightly more efficient
43 */
44
45 #include <stddef.h>
46 #include <pthread.h>
47
48 /* In this implementation, we use a single global mutex+condvar pair.
49 *
50 * Pros: portable and doesn't require playing with futexes, atomics
51 * and memory barriers.
52 *
53 * Cons: Slower than necessary.
54 */
55 static pthread_mutex_t sMutex = PTHREAD_RECURSIVE_MUTEX_INITIALIZER;
56 static pthread_cond_t sCond = PTHREAD_COND_INITIALIZER;
57
58
__cxa_guard_acquire(int volatile * gv)59 extern "C" int __cxa_guard_acquire(int volatile * gv)
60 {
61 pthread_mutex_lock(&sMutex);
62 for (;;) {
63 // while gv points to a volatile value, we use the
64 // previous pthread_mutex_lock or pthread_cond_wait
65 // as a trivial memory barrier
66 int guard = *gv;
67 if ((guard & 1) != 0) {
68 /* already initialized - return 0 */
69 pthread_mutex_unlock(&sMutex);
70 return 0;
71 }
72
73 // we use bit 8 to indicate that the guard value is being
74 // initialized, and bit 9 to indicate that there is another
75 // thread waiting for its completion.
76 if ((guard & 0x100) == 0) {
77 // nobody is initializing this yet, so mark the guard value
78 // first. and allow initialization to proceed.
79 *gv = 0x100;
80 pthread_mutex_unlock(&sMutex);
81 return 1;
82 }
83
84 // already being initialized by amother thread,
85 // we must indicate that there is a waiter, then
86 // wait to be woken up before trying again.
87 *gv = guard | 0x200;
88 pthread_cond_wait(&sCond, &sMutex);
89 }
90 }
91
__cxa_guard_release(int volatile * gv)92 extern "C" void __cxa_guard_release(int volatile * gv)
93 {
94 pthread_mutex_lock(&sMutex);
95
96 int guard = *gv;
97 // this indicates initialization for our two ABIs.
98 *gv = 0x1;
99 if ((guard & 0x200) != 0)
100 pthread_cond_broadcast(&sCond);
101
102 pthread_mutex_unlock(&sMutex);
103 }
104
__cxa_guard_abort(int volatile * gv)105 extern "C" void __cxa_guard_abort(int volatile * gv)
106 {
107 pthread_mutex_lock(&sMutex);
108
109 int guard = *gv;
110 *gv = 0;
111 if ((guard & 0x200) != 0)
112 pthread_cond_broadcast(&sCond);
113
114 pthread_mutex_unlock(&sMutex);
115 }
116