1/*
2 * Copyright 2006 The Android Open Source Project
3 */
4
5#include <stddef.h>
6#include <sys/atomics.h>
7#include <endian.h>
8#include <private/bionic_futex.h>
9#include <private/bionic_atomic_inline.h>
10
11// This file contains C++ ABI support functions for one time
12// constructors as defined in the "Run-time ABI for the ARM Architecture"
13// section 4.4.2
14//
15// ARM C++ ABI and Itanium/x86 C++ ABI has different definition for
16// one time construction:
17//
18//    ARM C++ ABI defines the LSB of guard variable should be tested
19//    by compiler-generated code before calling __cxa_guard_acquire et al.
20//
21//    The Itanium/x86 C++ ABI defines the low-order _byte_ should be
22//    tested instead.
23//
24//    Meanwhile, guard variable are 32bit aligned for ARM, and 64bit
25//    aligned for x86.
26//
27// Reference documentation:
28//
29//    section 3.2.3 of ARM IHI 0041C (for ARM)
30//    section 3.3.2 of the Itanium C++ ABI specification v1.83 (for x86).
31//
32// There is no C++ ABI available for other ARCH. But the gcc source
33// shows all other ARCH follow the definition of Itanium/x86 C++ ABI.
34
35
36#if defined(__arm__)
37// The ARM C++ ABI mandates that guard variable are
38// 32-bit aligned, 32-bit values. And only its LSB is tested by
39// the compiler-generated code before calling
40// __cxa_guard_acquire.
41//
42typedef union {
43    int volatile state;
44    int32_t aligner;
45} _guard_t;
46
47const static int ready = 0x1;
48const static int pending = 0x2;
49const static int waiting = 0x6;
50
51#else   // GCC sources indicates all none-arm follow the same ABI
52// The Itanium/x86 C++ ABI mandates that guard variables
53// are 64-bit aligned, 64-bit values. Also, the least-significant
54// byte is tested by the compiler-generated code before, we calling
55// __cxa_guard_acquire. We can access it through the first
56// 32-bit word in the union below.
57//
58typedef union {
59    int volatile state;
60    int64_t aligner;
61} _guard_t;
62
63const static int ready     = letoh32(0x1);
64const static int pending   = letoh32(0x100);
65const static int waiting   = letoh32(0x10000);
66#endif
67
68extern "C" int __cxa_guard_acquire(_guard_t* gv)
69{
70    // 0 -> pending, return 1
71    // pending -> waiting, wait and return 0
72    // waiting: untouched, wait and return 0
73    // ready: untouched, return 0
74
75retry:
76    if (__bionic_cmpxchg(0, pending, &gv->state) == 0) {
77        ANDROID_MEMBAR_FULL();
78        return 1;
79    }
80    __bionic_cmpxchg(pending, waiting, &gv->state); // Indicate there is a waiter
81    __futex_wait(&gv->state, waiting, NULL);
82
83    if (gv->state != ready) // __cxa_guard_abort was called, let every thread try since there is no return code for this condition
84        goto retry;
85
86    ANDROID_MEMBAR_FULL();
87    return 0;
88}
89
90extern "C" void __cxa_guard_release(_guard_t* gv)
91{
92    // pending -> ready
93    // waiting -> ready, and wake
94
95    ANDROID_MEMBAR_FULL();
96    if (__bionic_cmpxchg(pending, ready, &gv->state) == 0) {
97        return;
98    }
99
100    gv->state = ready;
101    __futex_wake(&gv->state, 0x7fffffff);
102}
103
104extern "C" void __cxa_guard_abort(_guard_t* gv)
105{
106    ANDROID_MEMBAR_FULL();
107    gv->state= 0;
108    __futex_wake(&gv->state, 0x7fffffff);
109}
110