1 // Copyright 2019 The Abseil Authors. 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // https://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 // 15 // ----------------------------------------------------------------------------- 16 // File: options.h 17 // ----------------------------------------------------------------------------- 18 // 19 // This file contains Abseil configuration options for setting specific 20 // implementations instead of letting Abseil determine which implementation to 21 // use at compile-time. Setting these options may be useful for package or build 22 // managers who wish to guarantee ABI stability within binary builds (which are 23 // otherwise difficult to enforce). 24 // 25 // *** IMPORTANT NOTICE FOR PACKAGE MANAGERS: It is important that 26 // maintainers of package managers who wish to package Abseil read and 27 // understand this file! *** 28 // 29 // Abseil contains a number of possible configuration endpoints, based on 30 // parameters such as the detected platform, language version, or command-line 31 // flags used to invoke the underlying binary. As is the case with all 32 // libraries, binaries which contain Abseil code must ensure that separate 33 // packages use the same compiled copy of Abseil to avoid a diamond dependency 34 // problem, which can occur if two packages built with different Abseil 35 // configuration settings are linked together. Diamond dependency problems in 36 // C++ may manifest as violations to the One Definition Rule (ODR) (resulting in 37 // linker errors), or undefined behavior (resulting in crashes). 38 // 39 // Diamond dependency problems can be avoided if all packages utilize the same 40 // exact version of Abseil. Building from source code with the same compilation 41 // parameters is the easiest way to avoid such dependency problems. However, for 42 // package managers who cannot control such compilation parameters, we are 43 // providing the file to allow you to inject ABI (Application Binary Interface) 44 // stability across builds. Settings options in this file will neither change 45 // API nor ABI, providing a stable copy of Abseil between packages. 46 // 47 // Care must be taken to keep options within these configurations isolated 48 // from any other dynamic settings, such as command-line flags which could alter 49 // these options. This file is provided specifically to help build and package 50 // managers provide a stable copy of Abseil within their libraries and binaries; 51 // other developers should not have need to alter the contents of this file. 52 // 53 // ----------------------------------------------------------------------------- 54 // Usage 55 // ----------------------------------------------------------------------------- 56 // 57 // For any particular package release, set the appropriate definitions within 58 // this file to whatever value makes the most sense for your package(s). Note 59 // that, by default, most of these options, at the moment, affect the 60 // implementation of types; future options may affect other implementation 61 // details. 62 // 63 // NOTE: the defaults within this file all assume that Abseil can select the 64 // proper Abseil implementation at compile-time, which will not be sufficient 65 // to guarantee ABI stability to package managers. 66 67 // SKIP_ABSL_INLINE_NAMESPACE_CHECK 68 69 #ifndef ABSL_BASE_OPTIONS_H_ 70 #define ABSL_BASE_OPTIONS_H_ 71 72 // ----------------------------------------------------------------------------- 73 // Type Compatibility Options 74 // ----------------------------------------------------------------------------- 75 76 // ABSL_OPTION_USE_STD_STRING_VIEW 77 // 78 // This option controls whether absl::string_view is implemented as an alias to 79 // std::string_view, or as an independent implementation. 80 // 81 // A value of 0 means to use Abseil's implementation. This requires only C++11 82 // support, and is expected to work on every toolchain we support. 83 // 84 // A value of 1 means to use an alias to std::string_view. This requires that 85 // all code using Abseil is built in C++17 mode or later. 86 // 87 // A value of 2 means to detect the C++ version being used to compile Abseil, 88 // and use an alias only if a working std::string_view is available. This 89 // option is useful when you are building your program from source. It should 90 // not be used otherwise -- for example, if you are distributing Abseil in a 91 // binary package manager -- since in mode 2, absl::string_view will name a 92 // different type, with a different mangled name and binary layout, depending on 93 // the compiler flags passed by the end user. For more info, see 94 // https://abseil.io/about/design/dropin-types. 95 // 96 // User code should not inspect this macro. To check in the preprocessor if 97 // absl::string_view is a typedef of std::string_view, use the feature macro 98 // ABSL_USES_STD_STRING_VIEW. 99 100 #define ABSL_OPTION_USE_STD_STRING_VIEW 2 101 102 // ABSL_OPTION_USE_STD_ORDERING 103 // 104 // This option controls whether absl::{partial,weak,strong}_ordering are 105 // implemented as aliases to the std:: ordering types, or as an independent 106 // implementation. 107 // 108 // A value of 0 means to use Abseil's implementation. This requires only C++11 109 // support, and is expected to work on every toolchain we support. 110 // 111 // A value of 1 means to use aliases. This requires that all code using Abseil 112 // is built in C++20 mode or later. 113 // 114 // A value of 2 means to detect the C++ version being used to compile Abseil, 115 // and use an alias only if working std:: ordering types are available. This 116 // option is useful when you are building your program from source. It should 117 // not be used otherwise -- for example, if you are distributing Abseil in a 118 // binary package manager -- since in mode 2, they will name different types, 119 // with different mangled names and binary layout, depending on the compiler 120 // flags passed by the end user. For more info, see 121 // https://abseil.io/about/design/dropin-types. 122 // 123 // User code should not inspect this macro. To check in the preprocessor if 124 // the ordering types are aliases of std:: ordering types, use the feature macro 125 // ABSL_USES_STD_ORDERING. 126 127 #define ABSL_OPTION_USE_STD_ORDERING 2 128 129 // ABSL_OPTION_USE_INLINE_NAMESPACE 130 // ABSL_OPTION_INLINE_NAMESPACE_NAME 131 // 132 // These options controls whether all entities in the absl namespace are 133 // contained within an inner inline namespace. This does not affect the 134 // user-visible API of Abseil, but it changes the mangled names of all symbols. 135 // 136 // This can be useful as a version tag if you are distributing Abseil in 137 // precompiled form. This will prevent a binary library build of Abseil with 138 // one inline namespace being used with headers configured with a different 139 // inline namespace name. Binary packagers are reminded that Abseil does not 140 // guarantee any ABI stability in Abseil, so any update of Abseil or 141 // configuration change in such a binary package should be combined with a 142 // new, unique value for the inline namespace name. 143 // 144 // A value of 0 means not to use inline namespaces. 145 // 146 // A value of 1 means to use an inline namespace with the given name inside 147 // namespace absl. If this is set, ABSL_OPTION_INLINE_NAMESPACE_NAME must also 148 // be changed to a new, unique identifier name. In particular "head" is not 149 // allowed. 150 151 #define ABSL_OPTION_USE_INLINE_NAMESPACE 0 152 #define ABSL_OPTION_INLINE_NAMESPACE_NAME head 153 154 // ABSL_OPTION_HARDENED 155 // 156 // This option enables a "hardened" build in release mode (in this context, 157 // release mode is defined as a build where the `NDEBUG` macro is defined). 158 // 159 // A value of 0 means that "hardened" mode is not enabled. 160 // 161 // A value of 1 means that "hardened" mode is enabled with all checks. 162 // 163 // A value of 2 means that "hardened" mode is partially enabled, with 164 // only a subset of checks chosen to minimize performance impact. 165 // 166 // Hardened builds have additional security checks enabled when `NDEBUG` is 167 // defined. Defining `NDEBUG` is normally used to turn `assert()` macro into a 168 // no-op, as well as disabling other bespoke program consistency checks. By 169 // defining ABSL_OPTION_HARDENED to 1, a select set of checks remain enabled in 170 // release mode. These checks guard against programming errors that may lead to 171 // security vulnerabilities. In release mode, when one of these programming 172 // errors is encountered, the program will immediately abort, possibly without 173 // any attempt at logging. 174 // 175 // The checks enabled by this option are not free; they do incur runtime cost. 176 // 177 // The checks enabled by this option are always active when `NDEBUG` is not 178 // defined, even in the case when ABSL_OPTION_HARDENED is defined to 0. The 179 // checks enabled by this option may abort the program in a different way and 180 // log additional information when `NDEBUG` is not defined. 181 182 #define ABSL_OPTION_HARDENED 1 183 184 #endif // ABSL_BASE_OPTIONS_H_ 185