// Copyright 2017 The Abseil Authors. // // Licensed under the Apache License, Version 2.0 (the "License"); // you may not use this file except in compliance with the License. // You may obtain a copy of the License at // // https://www.apache.org/licenses/LICENSE-2.0 // // Unless required by applicable law or agreed to in writing, software // distributed under the License is distributed on an "AS IS" BASIS, // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. // See the License for the specific language governing permissions and // limitations under the License. // // This header file defines macros for declaring attributes for functions, // types, and variables. // // These macros are used within Abseil and allow the compiler to optimize, where // applicable, certain function calls. // // This file is used for both C and C++! // // Most macros here are exposing GCC or Clang features, and are stubbed out for // other compilers. // // GCC attributes documentation: // https://gcc.gnu.org/onlinedocs/gcc-4.7.0/gcc/Function-Attributes.html // https://gcc.gnu.org/onlinedocs/gcc-4.7.0/gcc/Variable-Attributes.html // https://gcc.gnu.org/onlinedocs/gcc-4.7.0/gcc/Type-Attributes.html // // Most attributes in this file are already supported by GCC 4.7. However, some // of them are not supported in older version of Clang. Thus, we check // `__has_attribute()` first. If the check fails, we check if we are on GCC and // assume the attribute exists on GCC (which is verified on GCC 4.7). #ifndef ABSL_BASE_ATTRIBUTES_H_ #define ABSL_BASE_ATTRIBUTES_H_ #include "absl/base/config.h" // ABSL_HAVE_ATTRIBUTE // // A function-like feature checking macro that is a wrapper around // `__has_attribute`, which is defined by GCC 5+ and Clang and evaluates to a // nonzero constant integer if the attribute is supported or 0 if not. // // It evaluates to zero if `__has_attribute` is not defined by the compiler. // // GCC: https://gcc.gnu.org/gcc-5/changes.html // Clang: https://clang.llvm.org/docs/LanguageExtensions.html #ifdef __has_attribute #define ABSL_HAVE_ATTRIBUTE(x) __has_attribute(x) #else #define ABSL_HAVE_ATTRIBUTE(x) 0 #endif // ABSL_HAVE_CPP_ATTRIBUTE // // A function-like feature checking macro that accepts C++11 style attributes. // It's a wrapper around `__has_cpp_attribute`, defined by ISO C++ SD-6 // (https://en.cppreference.com/w/cpp/experimental/feature_test). If we don't // find `__has_cpp_attribute`, will evaluate to 0. #if defined(__cplusplus) && defined(__has_cpp_attribute) // NOTE: requiring __cplusplus above should not be necessary, but // works around https://bugs.llvm.org/show_bug.cgi?id=23435. #define ABSL_HAVE_CPP_ATTRIBUTE(x) __has_cpp_attribute(x) #else #define ABSL_HAVE_CPP_ATTRIBUTE(x) 0 #endif // ----------------------------------------------------------------------------- // Function Attributes // ----------------------------------------------------------------------------- // // GCC: https://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html // Clang: https://clang.llvm.org/docs/AttributeReference.html // ABSL_PRINTF_ATTRIBUTE // ABSL_SCANF_ATTRIBUTE // // Tells the compiler to perform `printf` format string checking if the // compiler supports it; see the 'format' attribute in // . // // Note: As the GCC manual states, "[s]ince non-static C++ methods // have an implicit 'this' argument, the arguments of such methods // should be counted from two, not one." #if ABSL_HAVE_ATTRIBUTE(format) || (defined(__GNUC__) && !defined(__clang__)) #define ABSL_PRINTF_ATTRIBUTE(string_index, first_to_check) \ __attribute__((__format__(__printf__, string_index, first_to_check))) #define ABSL_SCANF_ATTRIBUTE(string_index, first_to_check) \ __attribute__((__format__(__scanf__, string_index, first_to_check))) #else #define ABSL_PRINTF_ATTRIBUTE(string_index, first_to_check) #define ABSL_SCANF_ATTRIBUTE(string_index, first_to_check) #endif // ABSL_ATTRIBUTE_ALWAYS_INLINE // ABSL_ATTRIBUTE_NOINLINE // // Forces functions to either inline or not inline. Introduced in gcc 3.1. #if ABSL_HAVE_ATTRIBUTE(always_inline) || \ (defined(__GNUC__) && !defined(__clang__)) #define ABSL_ATTRIBUTE_ALWAYS_INLINE __attribute__((always_inline)) #define ABSL_HAVE_ATTRIBUTE_ALWAYS_INLINE 1 #else #define ABSL_ATTRIBUTE_ALWAYS_INLINE #endif #if ABSL_HAVE_ATTRIBUTE(noinline) || (defined(__GNUC__) && !defined(__clang__)) #define ABSL_ATTRIBUTE_NOINLINE __attribute__((noinline)) #define ABSL_HAVE_ATTRIBUTE_NOINLINE 1 #else #define ABSL_ATTRIBUTE_NOINLINE #endif // ABSL_ATTRIBUTE_NO_TAIL_CALL // // Prevents the compiler from optimizing away stack frames for functions which // end in a call to another function. #if ABSL_HAVE_ATTRIBUTE(disable_tail_calls) #define ABSL_HAVE_ATTRIBUTE_NO_TAIL_CALL 1 #define ABSL_ATTRIBUTE_NO_TAIL_CALL __attribute__((disable_tail_calls)) #elif defined(__GNUC__) && !defined(__clang__) #define ABSL_HAVE_ATTRIBUTE_NO_TAIL_CALL 1 #define ABSL_ATTRIBUTE_NO_TAIL_CALL \ __attribute__((optimize("no-optimize-sibling-calls"))) #else #define ABSL_ATTRIBUTE_NO_TAIL_CALL #define ABSL_HAVE_ATTRIBUTE_NO_TAIL_CALL 0 #endif // ABSL_ATTRIBUTE_WEAK // // Tags a function as weak for the purposes of compilation and linking. // Weak attributes currently do not work properly in LLVM's Windows backend, // so disable them there. See https://bugs.llvm.org/show_bug.cgi?id=37598 // for further information. // The MinGW compiler doesn't complain about the weak attribute until the link // step, presumably because Windows doesn't use ELF binaries. #if (ABSL_HAVE_ATTRIBUTE(weak) || \ (defined(__GNUC__) && !defined(__clang__))) && \ !(defined(__llvm__) && defined(_WIN32)) && !defined(__MINGW32__) #undef ABSL_ATTRIBUTE_WEAK #define ABSL_ATTRIBUTE_WEAK __attribute__((weak)) #define ABSL_HAVE_ATTRIBUTE_WEAK 1 #else #define ABSL_ATTRIBUTE_WEAK #define ABSL_HAVE_ATTRIBUTE_WEAK 0 #endif // ABSL_ATTRIBUTE_NONNULL // // Tells the compiler either (a) that a particular function parameter // should be a non-null pointer, or (b) that all pointer arguments should // be non-null. // // Note: As the GCC manual states, "[s]ince non-static C++ methods // have an implicit 'this' argument, the arguments of such methods // should be counted from two, not one." // // Args are indexed starting at 1. // // For non-static class member functions, the implicit `this` argument // is arg 1, and the first explicit argument is arg 2. For static class member // functions, there is no implicit `this`, and the first explicit argument is // arg 1. // // Example: // // /* arg_a cannot be null, but arg_b can */ // void Function(void* arg_a, void* arg_b) ABSL_ATTRIBUTE_NONNULL(1); // // class C { // /* arg_a cannot be null, but arg_b can */ // void Method(void* arg_a, void* arg_b) ABSL_ATTRIBUTE_NONNULL(2); // // /* arg_a cannot be null, but arg_b can */ // static void StaticMethod(void* arg_a, void* arg_b) // ABSL_ATTRIBUTE_NONNULL(1); // }; // // If no arguments are provided, then all pointer arguments should be non-null. // // /* No pointer arguments may be null. */ // void Function(void* arg_a, void* arg_b, int arg_c) ABSL_ATTRIBUTE_NONNULL(); // // NOTE: The GCC nonnull attribute actually accepts a list of arguments, but // ABSL_ATTRIBUTE_NONNULL does not. #if ABSL_HAVE_ATTRIBUTE(nonnull) || (defined(__GNUC__) && !defined(__clang__)) #define ABSL_ATTRIBUTE_NONNULL(arg_index) __attribute__((nonnull(arg_index))) #else #define ABSL_ATTRIBUTE_NONNULL(...) #endif // ABSL_ATTRIBUTE_NORETURN // // Tells the compiler that a given function never returns. #if ABSL_HAVE_ATTRIBUTE(noreturn) || (defined(__GNUC__) && !defined(__clang__)) #define ABSL_ATTRIBUTE_NORETURN __attribute__((noreturn)) #elif defined(_MSC_VER) #define ABSL_ATTRIBUTE_NORETURN __declspec(noreturn) #else #define ABSL_ATTRIBUTE_NORETURN #endif // ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS // // Tells the AddressSanitizer (or other memory testing tools) to ignore a given // function. Useful for cases when a function reads random locations on stack, // calls _exit from a cloned subprocess, deliberately accesses buffer // out of bounds or does other scary things with memory. // NOTE: GCC supports AddressSanitizer(asan) since 4.8. // https://gcc.gnu.org/gcc-4.8/changes.html #if ABSL_HAVE_ATTRIBUTE(no_sanitize_address) #define ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS __attribute__((no_sanitize_address)) #else #define ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS #endif // ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY // // Tells the MemorySanitizer to relax the handling of a given function. All "Use // of uninitialized value" warnings from such functions will be suppressed, and // all values loaded from memory will be considered fully initialized. This // attribute is similar to the ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS attribute // above, but deals with initialized-ness rather than addressability issues. // NOTE: MemorySanitizer(msan) is supported by Clang but not GCC. #if ABSL_HAVE_ATTRIBUTE(no_sanitize_memory) #define ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY __attribute__((no_sanitize_memory)) #else #define ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY #endif // ABSL_ATTRIBUTE_NO_SANITIZE_THREAD // // Tells the ThreadSanitizer to not instrument a given function. // NOTE: GCC supports ThreadSanitizer(tsan) since 4.8. // https://gcc.gnu.org/gcc-4.8/changes.html #if ABSL_HAVE_ATTRIBUTE(no_sanitize_thread) #define ABSL_ATTRIBUTE_NO_SANITIZE_THREAD __attribute__((no_sanitize_thread)) #else #define ABSL_ATTRIBUTE_NO_SANITIZE_THREAD #endif // ABSL_ATTRIBUTE_NO_SANITIZE_UNDEFINED // // Tells the UndefinedSanitizer to ignore a given function. Useful for cases // where certain behavior (eg. division by zero) is being used intentionally. // NOTE: GCC supports UndefinedBehaviorSanitizer(ubsan) since 4.9. // https://gcc.gnu.org/gcc-4.9/changes.html #if ABSL_HAVE_ATTRIBUTE(no_sanitize_undefined) #define ABSL_ATTRIBUTE_NO_SANITIZE_UNDEFINED \ __attribute__((no_sanitize_undefined)) #elif ABSL_HAVE_ATTRIBUTE(no_sanitize) #define ABSL_ATTRIBUTE_NO_SANITIZE_UNDEFINED \ __attribute__((no_sanitize("undefined"))) #else #define ABSL_ATTRIBUTE_NO_SANITIZE_UNDEFINED #endif // ABSL_ATTRIBUTE_NO_SANITIZE_CFI // // Tells the ControlFlowIntegrity sanitizer to not instrument a given function. // See https://clang.llvm.org/docs/ControlFlowIntegrity.html for details. #if ABSL_HAVE_ATTRIBUTE(no_sanitize) #define ABSL_ATTRIBUTE_NO_SANITIZE_CFI __attribute__((no_sanitize("cfi"))) #else #define ABSL_ATTRIBUTE_NO_SANITIZE_CFI #endif // ABSL_ATTRIBUTE_NO_SANITIZE_SAFESTACK // // Tells the SafeStack to not instrument a given function. // See https://clang.llvm.org/docs/SafeStack.html for details. #if ABSL_HAVE_ATTRIBUTE(no_sanitize) #define ABSL_ATTRIBUTE_NO_SANITIZE_SAFESTACK \ __attribute__((no_sanitize("safe-stack"))) #else #define ABSL_ATTRIBUTE_NO_SANITIZE_SAFESTACK #endif // ABSL_ATTRIBUTE_RETURNS_NONNULL // // Tells the compiler that a particular function never returns a null pointer. #if ABSL_HAVE_ATTRIBUTE(returns_nonnull) || \ (defined(__GNUC__) && \ (__GNUC__ > 5 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 9)) && \ !defined(__clang__)) #define ABSL_ATTRIBUTE_RETURNS_NONNULL __attribute__((returns_nonnull)) #else #define ABSL_ATTRIBUTE_RETURNS_NONNULL #endif // ABSL_HAVE_ATTRIBUTE_SECTION // // Indicates whether labeled sections are supported. Weak symbol support is // a prerequisite. Labeled sections are not supported on Darwin/iOS. #ifdef ABSL_HAVE_ATTRIBUTE_SECTION #error ABSL_HAVE_ATTRIBUTE_SECTION cannot be directly set #elif (ABSL_HAVE_ATTRIBUTE(section) || \ (defined(__GNUC__) && !defined(__clang__))) && \ !defined(__APPLE__) && ABSL_HAVE_ATTRIBUTE_WEAK #define ABSL_HAVE_ATTRIBUTE_SECTION 1 // ABSL_ATTRIBUTE_SECTION // // Tells the compiler/linker to put a given function into a section and define // `__start_ ## name` and `__stop_ ## name` symbols to bracket the section. // This functionality is supported by GNU linker. Any function annotated with // `ABSL_ATTRIBUTE_SECTION` must not be inlined, or it will be placed into // whatever section its caller is placed into. // #ifndef ABSL_ATTRIBUTE_SECTION #define ABSL_ATTRIBUTE_SECTION(name) \ __attribute__((section(#name))) __attribute__((noinline)) #endif // ABSL_ATTRIBUTE_SECTION_VARIABLE // // Tells the compiler/linker to put a given variable into a section and define // `__start_ ## name` and `__stop_ ## name` symbols to bracket the section. // This functionality is supported by GNU linker. #ifndef ABSL_ATTRIBUTE_SECTION_VARIABLE #define ABSL_ATTRIBUTE_SECTION_VARIABLE(name) __attribute__((section(#name))) #endif // ABSL_DECLARE_ATTRIBUTE_SECTION_VARS // // A weak section declaration to be used as a global declaration // for ABSL_ATTRIBUTE_SECTION_START|STOP(name) to compile and link // even without functions with ABSL_ATTRIBUTE_SECTION(name). // ABSL_DEFINE_ATTRIBUTE_SECTION should be in the exactly one file; it's // a no-op on ELF but not on Mach-O. // #ifndef ABSL_DECLARE_ATTRIBUTE_SECTION_VARS #define ABSL_DECLARE_ATTRIBUTE_SECTION_VARS(name) \ extern char __start_##name[] ABSL_ATTRIBUTE_WEAK; \ extern char __stop_##name[] ABSL_ATTRIBUTE_WEAK #endif #ifndef ABSL_DEFINE_ATTRIBUTE_SECTION_VARS #define ABSL_INIT_ATTRIBUTE_SECTION_VARS(name) #define ABSL_DEFINE_ATTRIBUTE_SECTION_VARS(name) #endif // ABSL_ATTRIBUTE_SECTION_START // // Returns `void*` pointers to start/end of a section of code with // functions having ABSL_ATTRIBUTE_SECTION(name). // Returns 0 if no such functions exist. // One must ABSL_DECLARE_ATTRIBUTE_SECTION_VARS(name) for this to compile and // link. // #define ABSL_ATTRIBUTE_SECTION_START(name) \ (reinterpret_cast(__start_##name)) #define ABSL_ATTRIBUTE_SECTION_STOP(name) \ (reinterpret_cast(__stop_##name)) #else // !ABSL_HAVE_ATTRIBUTE_SECTION #define ABSL_HAVE_ATTRIBUTE_SECTION 0 // provide dummy definitions #define ABSL_ATTRIBUTE_SECTION(name) #define ABSL_ATTRIBUTE_SECTION_VARIABLE(name) #define ABSL_INIT_ATTRIBUTE_SECTION_VARS(name) #define ABSL_DEFINE_ATTRIBUTE_SECTION_VARS(name) #define ABSL_DECLARE_ATTRIBUTE_SECTION_VARS(name) #define ABSL_ATTRIBUTE_SECTION_START(name) (reinterpret_cast(0)) #define ABSL_ATTRIBUTE_SECTION_STOP(name) (reinterpret_cast(0)) #endif // ABSL_ATTRIBUTE_SECTION // ABSL_ATTRIBUTE_STACK_ALIGN_FOR_OLD_LIBC // // Support for aligning the stack on 32-bit x86. #if ABSL_HAVE_ATTRIBUTE(force_align_arg_pointer) || \ (defined(__GNUC__) && !defined(__clang__)) #if defined(__i386__) #define ABSL_ATTRIBUTE_STACK_ALIGN_FOR_OLD_LIBC \ __attribute__((force_align_arg_pointer)) #define ABSL_REQUIRE_STACK_ALIGN_TRAMPOLINE (0) #elif defined(__x86_64__) #define ABSL_REQUIRE_STACK_ALIGN_TRAMPOLINE (1) #define ABSL_ATTRIBUTE_STACK_ALIGN_FOR_OLD_LIBC #else // !__i386__ && !__x86_64 #define ABSL_REQUIRE_STACK_ALIGN_TRAMPOLINE (0) #define ABSL_ATTRIBUTE_STACK_ALIGN_FOR_OLD_LIBC #endif // __i386__ #else #define ABSL_ATTRIBUTE_STACK_ALIGN_FOR_OLD_LIBC #define ABSL_REQUIRE_STACK_ALIGN_TRAMPOLINE (0) #endif // ABSL_MUST_USE_RESULT // // Tells the compiler to warn about unused results. // // When annotating a function, it must appear as the first part of the // declaration or definition. The compiler will warn if the return value from // such a function is unused: // // ABSL_MUST_USE_RESULT Sprocket* AllocateSprocket(); // AllocateSprocket(); // Triggers a warning. // // When annotating a class, it is equivalent to annotating every function which // returns an instance. // // class ABSL_MUST_USE_RESULT Sprocket {}; // Sprocket(); // Triggers a warning. // // Sprocket MakeSprocket(); // MakeSprocket(); // Triggers a warning. // // Note that references and pointers are not instances: // // Sprocket* SprocketPointer(); // SprocketPointer(); // Does *not* trigger a warning. // // ABSL_MUST_USE_RESULT allows using cast-to-void to suppress the unused result // warning. For that, warn_unused_result is used only for clang but not for gcc. // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66425 // // Note: past advice was to place the macro after the argument list. #if ABSL_HAVE_ATTRIBUTE(nodiscard) #define ABSL_MUST_USE_RESULT [[nodiscard]] #elif defined(__clang__) && ABSL_HAVE_ATTRIBUTE(warn_unused_result) #define ABSL_MUST_USE_RESULT __attribute__((warn_unused_result)) #else #define ABSL_MUST_USE_RESULT #endif // ABSL_ATTRIBUTE_HOT, ABSL_ATTRIBUTE_COLD // // Tells GCC that a function is hot or cold. GCC can use this information to // improve static analysis, i.e. a conditional branch to a cold function // is likely to be not-taken. // This annotation is used for function declarations. // // Example: // // int foo() ABSL_ATTRIBUTE_HOT; #if ABSL_HAVE_ATTRIBUTE(hot) || (defined(__GNUC__) && !defined(__clang__)) #define ABSL_ATTRIBUTE_HOT __attribute__((hot)) #else #define ABSL_ATTRIBUTE_HOT #endif #if ABSL_HAVE_ATTRIBUTE(cold) || (defined(__GNUC__) && !defined(__clang__)) #define ABSL_ATTRIBUTE_COLD __attribute__((cold)) #else #define ABSL_ATTRIBUTE_COLD #endif // ABSL_XRAY_ALWAYS_INSTRUMENT, ABSL_XRAY_NEVER_INSTRUMENT, ABSL_XRAY_LOG_ARGS // // We define the ABSL_XRAY_ALWAYS_INSTRUMENT and ABSL_XRAY_NEVER_INSTRUMENT // macro used as an attribute to mark functions that must always or never be // instrumented by XRay. Currently, this is only supported in Clang/LLVM. // // For reference on the LLVM XRay instrumentation, see // http://llvm.org/docs/XRay.html. // // A function with the XRAY_ALWAYS_INSTRUMENT macro attribute in its declaration // will always get the XRay instrumentation sleds. These sleds may introduce // some binary size and runtime overhead and must be used sparingly. // // These attributes only take effect when the following conditions are met: // // * The file/target is built in at least C++11 mode, with a Clang compiler // that supports XRay attributes. // * The file/target is built with the -fxray-instrument flag set for the // Clang/LLVM compiler. // * The function is defined in the translation unit (the compiler honors the // attribute in either the definition or the declaration, and must match). // // There are cases when, even when building with XRay instrumentation, users // might want to control specifically which functions are instrumented for a // particular build using special-case lists provided to the compiler. These // special case lists are provided to Clang via the // -fxray-always-instrument=... and -fxray-never-instrument=... flags. The // attributes in source take precedence over these special-case lists. // // To disable the XRay attributes at build-time, users may define // ABSL_NO_XRAY_ATTRIBUTES. Do NOT define ABSL_NO_XRAY_ATTRIBUTES on specific // packages/targets, as this may lead to conflicting definitions of functions at // link-time. // // XRay isn't currently supported on Android: // https://github.com/android/ndk/issues/368 #if ABSL_HAVE_CPP_ATTRIBUTE(clang::xray_always_instrument) && \ !defined(ABSL_NO_XRAY_ATTRIBUTES) && !defined(__ANDROID__) #define ABSL_XRAY_ALWAYS_INSTRUMENT [[clang::xray_always_instrument]] #define ABSL_XRAY_NEVER_INSTRUMENT [[clang::xray_never_instrument]] #if ABSL_HAVE_CPP_ATTRIBUTE(clang::xray_log_args) #define ABSL_XRAY_LOG_ARGS(N) \ [[clang::xray_always_instrument, clang::xray_log_args(N)]] #else #define ABSL_XRAY_LOG_ARGS(N) [[clang::xray_always_instrument]] #endif #else #define ABSL_XRAY_ALWAYS_INSTRUMENT #define ABSL_XRAY_NEVER_INSTRUMENT #define ABSL_XRAY_LOG_ARGS(N) #endif // ABSL_ATTRIBUTE_REINITIALIZES // // Indicates that a member function reinitializes the entire object to a known // state, independent of the previous state of the object. // // The clang-tidy check bugprone-use-after-move allows member functions marked // with this attribute to be called on objects that have been moved from; // without the attribute, this would result in a use-after-move warning. #if ABSL_HAVE_CPP_ATTRIBUTE(clang::reinitializes) #define ABSL_ATTRIBUTE_REINITIALIZES [[clang::reinitializes]] #else #define ABSL_ATTRIBUTE_REINITIALIZES #endif // ----------------------------------------------------------------------------- // Variable Attributes // ----------------------------------------------------------------------------- // ABSL_ATTRIBUTE_UNUSED // // Prevents the compiler from complaining about variables that appear unused. #if ABSL_HAVE_ATTRIBUTE(unused) || (defined(__GNUC__) && !defined(__clang__)) #undef ABSL_ATTRIBUTE_UNUSED #define ABSL_ATTRIBUTE_UNUSED __attribute__((__unused__)) #else #define ABSL_ATTRIBUTE_UNUSED #endif // ABSL_ATTRIBUTE_INITIAL_EXEC // // Tells the compiler to use "initial-exec" mode for a thread-local variable. // See http://people.redhat.com/drepper/tls.pdf for the gory details. #if ABSL_HAVE_ATTRIBUTE(tls_model) || (defined(__GNUC__) && !defined(__clang__)) #define ABSL_ATTRIBUTE_INITIAL_EXEC __attribute__((tls_model("initial-exec"))) #else #define ABSL_ATTRIBUTE_INITIAL_EXEC #endif // ABSL_ATTRIBUTE_PACKED // // Instructs the compiler not to use natural alignment for a tagged data // structure, but instead to reduce its alignment to 1. This attribute can // either be applied to members of a structure or to a structure in its // entirety. Applying this attribute (judiciously) to a structure in its // entirety to optimize the memory footprint of very commonly-used structs is // fine. Do not apply this attribute to a structure in its entirety if the // purpose is to control the offsets of the members in the structure. Instead, // apply this attribute only to structure members that need it. // // When applying ABSL_ATTRIBUTE_PACKED only to specific structure members the // natural alignment of structure members not annotated is preserved. Aligned // member accesses are faster than non-aligned member accesses even if the // targeted microprocessor supports non-aligned accesses. #if ABSL_HAVE_ATTRIBUTE(packed) || (defined(__GNUC__) && !defined(__clang__)) #define ABSL_ATTRIBUTE_PACKED __attribute__((__packed__)) #else #define ABSL_ATTRIBUTE_PACKED #endif // ABSL_ATTRIBUTE_FUNC_ALIGN // // Tells the compiler to align the function start at least to certain // alignment boundary #if ABSL_HAVE_ATTRIBUTE(aligned) || (defined(__GNUC__) && !defined(__clang__)) #define ABSL_ATTRIBUTE_FUNC_ALIGN(bytes) __attribute__((aligned(bytes))) #else #define ABSL_ATTRIBUTE_FUNC_ALIGN(bytes) #endif // ABSL_FALLTHROUGH_INTENDED // // Annotates implicit fall-through between switch labels, allowing a case to // indicate intentional fallthrough and turn off warnings about any lack of a // `break` statement. The ABSL_FALLTHROUGH_INTENDED macro should be followed by // a semicolon and can be used in most places where `break` can, provided that // no statements exist between it and the next switch label. // // Example: // // switch (x) { // case 40: // case 41: // if (truth_is_out_there) { // ++x; // ABSL_FALLTHROUGH_INTENDED; // Use instead of/along with annotations // // in comments // } else { // return x; // } // case 42: // ... // // Notes: when compiled with clang in C++11 mode, the ABSL_FALLTHROUGH_INTENDED // macro is expanded to the [[clang::fallthrough]] attribute, which is analysed // when performing switch labels fall-through diagnostic // (`-Wimplicit-fallthrough`). See clang documentation on language extensions // for details: // https://clang.llvm.org/docs/AttributeReference.html#fallthrough-clang-fallthrough // // When used with unsupported compilers, the ABSL_FALLTHROUGH_INTENDED macro // has no effect on diagnostics. In any case this macro has no effect on runtime // behavior and performance of code. #ifdef ABSL_FALLTHROUGH_INTENDED #error "ABSL_FALLTHROUGH_INTENDED should not be defined." #endif // TODO(zhangxy): Use c++17 standard [[fallthrough]] macro, when supported. #if defined(__clang__) && defined(__has_warning) #if __has_feature(cxx_attributes) && __has_warning("-Wimplicit-fallthrough") #define ABSL_FALLTHROUGH_INTENDED [[clang::fallthrough]] #endif #elif defined(__GNUC__) && __GNUC__ >= 7 #define ABSL_FALLTHROUGH_INTENDED [[gnu::fallthrough]] #endif #ifndef ABSL_FALLTHROUGH_INTENDED #define ABSL_FALLTHROUGH_INTENDED \ do { \ } while (0) #endif // ABSL_DEPRECATED() // // Marks a deprecated class, struct, enum, function, method and variable // declarations. The macro argument is used as a custom diagnostic message (e.g. // suggestion of a better alternative). // // Examples: // // class ABSL_DEPRECATED("Use Bar instead") Foo {...}; // // ABSL_DEPRECATED("Use Baz() instead") void Bar() {...} // // template // ABSL_DEPRECATED("Use DoThat() instead") // void DoThis(); // // Every usage of a deprecated entity will trigger a warning when compiled with // clang's `-Wdeprecated-declarations` option. This option is turned off by // default, but the warnings will be reported by clang-tidy. #if defined(__clang__) && __cplusplus >= 201103L #define ABSL_DEPRECATED(message) __attribute__((deprecated(message))) #endif #ifndef ABSL_DEPRECATED #define ABSL_DEPRECATED(message) #endif // ABSL_CONST_INIT // // A variable declaration annotated with the `ABSL_CONST_INIT` attribute will // not compile (on supported platforms) unless the variable has a constant // initializer. This is useful for variables with static and thread storage // duration, because it guarantees that they will not suffer from the so-called // "static init order fiasco". Prefer to put this attribute on the most visible // declaration of the variable, if there's more than one, because code that // accesses the variable can then use the attribute for optimization. // // Example: // // class MyClass { // public: // ABSL_CONST_INIT static MyType my_var; // }; // // MyType MyClass::my_var = MakeMyType(...); // // Note that this attribute is redundant if the variable is declared constexpr. #if ABSL_HAVE_CPP_ATTRIBUTE(clang::require_constant_initialization) #define ABSL_CONST_INIT [[clang::require_constant_initialization]] #else #define ABSL_CONST_INIT #endif // ABSL_HAVE_CPP_ATTRIBUTE(clang::require_constant_initialization) #endif // ABSL_BASE_ATTRIBUTES_H_