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213516ef | 1 | /* Copyright (C) 2022-2023 Free Software Foundation, Inc. |
68c0faca PA |
2 | |
3 | This file is part of GDB. | |
4 | ||
5 | This program is free software; you can redistribute it and/or modify | |
6 | it under the terms of the GNU General Public License as published by | |
7 | the Free Software Foundation; either version 3 of the License, or | |
8 | (at your option) any later version. | |
9 | ||
10 | This program is distributed in the hope that it will be useful, | |
11 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
13 | GNU General Public License for more details. | |
14 | ||
15 | You should have received a copy of the GNU General Public License | |
16 | along with this program. If not, see <http://www.gnu.org/licenses/>. */ | |
17 | ||
18 | #ifndef PACKED_H | |
19 | #define PACKED_H | |
20 | ||
02f0597c | 21 | #include "traits.h" |
e249e6b8 | 22 | #include <atomic> |
02f0597c | 23 | |
68c0faca PA |
24 | /* Each instantiation and full specialization of the packed template |
25 | defines a type that behaves like a given scalar type, but that has | |
26 | byte alignment, and, may optionally have a smaller size than the | |
27 | given scalar type. This is typically used as alternative to | |
28 | bit-fields (and ENUM_BITFIELD), when the fields must have separate | |
29 | memory locations to avoid data races. */ | |
30 | ||
b669667d PA |
31 | /* There are two implementations here -- one standard compliant, using |
32 | a byte array for internal representation, and another that relies | |
33 | on bitfields and attribute packed (and attribute gcc_struct on | |
34 | Windows). The latter is preferable, as it is more convenient when | |
35 | debugging GDB -- printing a struct packed variable prints its field | |
36 | using its natural type, which is particularly useful if the type is | |
37 | an enum -- but may not work on all compilers. */ | |
38 | ||
39 | /* Clang targeting Windows does not support attribute gcc_struct, so | |
33b5899f | 40 | we use the alternative byte array implementation there. */ |
b669667d PA |
41 | #if defined _WIN32 && defined __clang__ |
42 | # define PACKED_USE_ARRAY 1 | |
43 | #else | |
44 | # define PACKED_USE_ARRAY 0 | |
45 | #endif | |
46 | ||
47 | /* For the preferred implementation, we need gcc_struct on Windows, as | |
48 | otherwise the size of e.g., "packed<int, 1>" will be larger than | |
49 | what we want. Clang targeting Windows does not support attribute | |
50 | gcc_struct. */ | |
51 | #if !PACKED_USE_ARRAY && defined _WIN32 && !defined __clang__ | |
4ca26ad7 PA |
52 | # define ATTRIBUTE_GCC_STRUCT __attribute__((__gcc_struct__)) |
53 | #else | |
54 | # define ATTRIBUTE_GCC_STRUCT | |
55 | #endif | |
56 | ||
68c0faca | 57 | template<typename T, size_t Bytes = sizeof (T)> |
4ca26ad7 | 58 | struct ATTRIBUTE_GCC_STRUCT packed |
68c0faca PA |
59 | { |
60 | public: | |
2df41bda TV |
61 | packed () noexcept = default; |
62 | ||
68c0faca PA |
63 | packed (T val) |
64 | { | |
b669667d PA |
65 | gdb_static_assert (sizeof (ULONGEST) >= sizeof (T)); |
66 | ||
67 | #if PACKED_USE_ARRAY | |
68 | ULONGEST tmp = val; | |
69 | for (int i = (Bytes - 1); i >= 0; --i) | |
70 | { | |
71 | m_bytes[i] = (gdb_byte) tmp; | |
72 | tmp >>= HOST_CHAR_BIT; | |
73 | } | |
74 | #else | |
68c0faca | 75 | m_val = val; |
b669667d | 76 | #endif |
68c0faca PA |
77 | |
78 | /* Ensure size and aligment are what we expect. */ | |
79 | gdb_static_assert (sizeof (packed) == Bytes); | |
80 | gdb_static_assert (alignof (packed) == 1); | |
81 | ||
82 | /* Make sure packed can be wrapped with std::atomic. */ | |
02f0597c | 83 | #if HAVE_IS_TRIVIALLY_COPYABLE |
68c0faca | 84 | gdb_static_assert (std::is_trivially_copyable<packed>::value); |
02f0597c | 85 | #endif |
68c0faca PA |
86 | gdb_static_assert (std::is_copy_constructible<packed>::value); |
87 | gdb_static_assert (std::is_move_constructible<packed>::value); | |
88 | gdb_static_assert (std::is_copy_assignable<packed>::value); | |
89 | gdb_static_assert (std::is_move_assignable<packed>::value); | |
90 | } | |
91 | ||
92 | operator T () const noexcept | |
93 | { | |
b669667d PA |
94 | #if PACKED_USE_ARRAY |
95 | ULONGEST tmp = 0; | |
96 | for (int i = 0;;) | |
97 | { | |
98 | tmp |= m_bytes[i]; | |
99 | if (++i == Bytes) | |
100 | break; | |
101 | tmp <<= HOST_CHAR_BIT; | |
102 | } | |
103 | return (T) tmp; | |
104 | #else | |
68c0faca | 105 | return m_val; |
b669667d | 106 | #endif |
68c0faca PA |
107 | } |
108 | ||
109 | private: | |
b669667d PA |
110 | #if PACKED_USE_ARRAY |
111 | gdb_byte m_bytes[Bytes]; | |
112 | #else | |
68c0faca | 113 | T m_val : (Bytes * HOST_CHAR_BIT) ATTRIBUTE_PACKED; |
b669667d | 114 | #endif |
68c0faca PA |
115 | }; |
116 | ||
e249e6b8 PA |
117 | /* Add some comparisons between std::atomic<packed<T>> and packed<T> |
118 | and T. We need this because even though std::atomic<T> doesn't | |
119 | define these operators, the relational expressions still work via | |
120 | implicit conversions. Those wouldn't work when wrapped in packed | |
121 | without these operators, because they'd require two implicit | |
122 | conversions to go from T to packed<T> to std::atomic<packed<T>> | |
123 | (and back), and C++ only does one. */ | |
124 | ||
125 | #define PACKED_ATOMIC_OP(OP) \ | |
126 | template<typename T, size_t Bytes> \ | |
127 | bool operator OP (const std::atomic<packed<T, Bytes>> &lhs, \ | |
128 | const std::atomic<packed<T, Bytes>> &rhs) \ | |
129 | { \ | |
130 | return lhs.load () OP rhs.load (); \ | |
131 | } \ | |
132 | \ | |
133 | template<typename T, size_t Bytes> \ | |
134 | bool operator OP (T lhs, const std::atomic<packed<T, Bytes>> &rhs) \ | |
135 | { \ | |
136 | return lhs OP rhs.load (); \ | |
137 | } \ | |
138 | \ | |
139 | template<typename T, size_t Bytes> \ | |
140 | bool operator OP (const std::atomic<packed<T, Bytes>> &lhs, T rhs) \ | |
141 | { \ | |
142 | return lhs.load () OP rhs; \ | |
143 | } \ | |
144 | \ | |
145 | template<typename T, size_t Bytes> \ | |
146 | bool operator OP (const std::atomic<packed<T, Bytes>> &lhs, \ | |
147 | packed<T, Bytes> rhs) \ | |
148 | { \ | |
149 | return lhs.load () OP rhs; \ | |
150 | } \ | |
151 | \ | |
152 | template<typename T, size_t Bytes> \ | |
153 | bool operator OP (packed<T, Bytes> lhs, \ | |
154 | const std::atomic<packed<T, Bytes>> &rhs) \ | |
155 | { \ | |
156 | return lhs OP rhs.load (); \ | |
157 | } | |
68c0faca | 158 | |
e249e6b8 PA |
159 | PACKED_ATOMIC_OP (==) |
160 | PACKED_ATOMIC_OP (!=) | |
161 | PACKED_ATOMIC_OP (>) | |
162 | PACKED_ATOMIC_OP (<) | |
163 | PACKED_ATOMIC_OP (>=) | |
164 | PACKED_ATOMIC_OP (<=) | |
68c0faca | 165 | |
e249e6b8 | 166 | #undef PACKED_ATOMIC_OP |
68c0faca PA |
167 | |
168 | #endif |