1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
|
/* Copyright (C) 2022 Free Software Foundation, Inc.
This file is part of GDB.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#ifndef PACKED_H
#define PACKED_H
#include "traits.h"
#include <atomic>
/* Each instantiation and full specialization of the packed template
defines a type that behaves like a given scalar type, but that has
byte alignment, and, may optionally have a smaller size than the
given scalar type. This is typically used as alternative to
bit-fields (and ENUM_BITFIELD), when the fields must have separate
memory locations to avoid data races. */
/* There are two implementations here -- one standard compliant, using
a byte array for internal representation, and another that relies
on bitfields and attribute packed (and attribute gcc_struct on
Windows). The latter is preferable, as it is more convenient when
debugging GDB -- printing a struct packed variable prints its field
using its natural type, which is particularly useful if the type is
an enum -- but may not work on all compilers. */
/* Clang targeting Windows does not support attribute gcc_struct, so
we use the alternative byte array implemention there. */
#if defined _WIN32 && defined __clang__
# define PACKED_USE_ARRAY 1
#else
# define PACKED_USE_ARRAY 0
#endif
/* For the preferred implementation, we need gcc_struct on Windows, as
otherwise the size of e.g., "packed<int, 1>" will be larger than
what we want. Clang targeting Windows does not support attribute
gcc_struct. */
#if !PACKED_USE_ARRAY && defined _WIN32 && !defined __clang__
# define ATTRIBUTE_GCC_STRUCT __attribute__((__gcc_struct__))
#else
# define ATTRIBUTE_GCC_STRUCT
#endif
template<typename T, size_t Bytes = sizeof (T)>
struct ATTRIBUTE_GCC_STRUCT packed
{
public:
packed () noexcept = default;
packed (T val)
{
gdb_static_assert (sizeof (ULONGEST) >= sizeof (T));
#if PACKED_USE_ARRAY
ULONGEST tmp = val;
for (int i = (Bytes - 1); i >= 0; --i)
{
m_bytes[i] = (gdb_byte) tmp;
tmp >>= HOST_CHAR_BIT;
}
#else
m_val = val;
#endif
/* Ensure size and aligment are what we expect. */
gdb_static_assert (sizeof (packed) == Bytes);
gdb_static_assert (alignof (packed) == 1);
/* Make sure packed can be wrapped with std::atomic. */
#if HAVE_IS_TRIVIALLY_COPYABLE
gdb_static_assert (std::is_trivially_copyable<packed>::value);
#endif
gdb_static_assert (std::is_copy_constructible<packed>::value);
gdb_static_assert (std::is_move_constructible<packed>::value);
gdb_static_assert (std::is_copy_assignable<packed>::value);
gdb_static_assert (std::is_move_assignable<packed>::value);
}
operator T () const noexcept
{
#if PACKED_USE_ARRAY
ULONGEST tmp = 0;
for (int i = 0;;)
{
tmp |= m_bytes[i];
if (++i == Bytes)
break;
tmp <<= HOST_CHAR_BIT;
}
return (T) tmp;
#else
return m_val;
#endif
}
private:
#if PACKED_USE_ARRAY
gdb_byte m_bytes[Bytes];
#else
T m_val : (Bytes * HOST_CHAR_BIT) ATTRIBUTE_PACKED;
#endif
};
/* Add some comparisons between std::atomic<packed<T>> and packed<T>
and T. We need this because even though std::atomic<T> doesn't
define these operators, the relational expressions still work via
implicit conversions. Those wouldn't work when wrapped in packed
without these operators, because they'd require two implicit
conversions to go from T to packed<T> to std::atomic<packed<T>>
(and back), and C++ only does one. */
#define PACKED_ATOMIC_OP(OP) \
template<typename T, size_t Bytes> \
bool operator OP (const std::atomic<packed<T, Bytes>> &lhs, \
const std::atomic<packed<T, Bytes>> &rhs) \
{ \
return lhs.load () OP rhs.load (); \
} \
\
template<typename T, size_t Bytes> \
bool operator OP (T lhs, const std::atomic<packed<T, Bytes>> &rhs) \
{ \
return lhs OP rhs.load (); \
} \
\
template<typename T, size_t Bytes> \
bool operator OP (const std::atomic<packed<T, Bytes>> &lhs, T rhs) \
{ \
return lhs.load () OP rhs; \
} \
\
template<typename T, size_t Bytes> \
bool operator OP (const std::atomic<packed<T, Bytes>> &lhs, \
packed<T, Bytes> rhs) \
{ \
return lhs.load () OP rhs; \
} \
\
template<typename T, size_t Bytes> \
bool operator OP (packed<T, Bytes> lhs, \
const std::atomic<packed<T, Bytes>> &rhs) \
{ \
return lhs OP rhs.load (); \
}
PACKED_ATOMIC_OP (==)
PACKED_ATOMIC_OP (!=)
PACKED_ATOMIC_OP (>)
PACKED_ATOMIC_OP (<)
PACKED_ATOMIC_OP (>=)
PACKED_ATOMIC_OP (<=)
#undef PACKED_ATOMIC_OP
#endif
|
