1 // Copyright 2017 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 // This header file defines macros for declaring attributes for functions, 16 // types, and variables. 17 // 18 // These macros are used within Abseil and allow the compiler to optimize, where 19 // applicable, certain function calls. 20 // 21 // Most macros here are exposing GCC or Clang features, and are stubbed out for 22 // other compilers. 23 // 24 // GCC attributes documentation: 25 // https://gcc.gnu.org/onlinedocs/gcc-4.7.0/gcc/Function-Attributes.html 26 // https://gcc.gnu.org/onlinedocs/gcc-4.7.0/gcc/Variable-Attributes.html 27 // https://gcc.gnu.org/onlinedocs/gcc-4.7.0/gcc/Type-Attributes.html 28 // 29 // Most attributes in this file are already supported by GCC 4.7. However, some 30 // of them are not supported in older version of Clang. Thus, we check 31 // `__has_attribute()` first. If the check fails, we check if we are on GCC and 32 // assume the attribute exists on GCC (which is verified on GCC 4.7). 33 34 #ifndef ABSL_BASE_ATTRIBUTES_H_ 35 #define ABSL_BASE_ATTRIBUTES_H_ 36 37 #include "absl/base/config.h" 38 39 // ABSL_HAVE_ATTRIBUTE 40 // 41 // A function-like feature checking macro that is a wrapper around 42 // `__has_attribute`, which is defined by GCC 5+ and Clang and evaluates to a 43 // nonzero constant integer if the attribute is supported or 0 if not. 44 // 45 // It evaluates to zero if `__has_attribute` is not defined by the compiler. 46 // 47 // GCC: https://gcc.gnu.org/gcc-5/changes.html 48 // Clang: https://clang.llvm.org/docs/LanguageExtensions.html 49 #ifdef __has_attribute 50 #define ABSL_HAVE_ATTRIBUTE(x) __has_attribute(x) 51 #else 52 #define ABSL_HAVE_ATTRIBUTE(x) 0 53 #endif 54 55 // ABSL_HAVE_CPP_ATTRIBUTE 56 // 57 // A function-like feature checking macro that accepts C++11 style attributes. 58 // It's a wrapper around `__has_cpp_attribute`, defined by ISO C++ SD-6 59 // (https://en.cppreference.com/w/cpp/experimental/feature_test). If we don't 60 // find `__has_cpp_attribute`, will evaluate to 0. 61 #if defined(__cplusplus) && defined(__has_cpp_attribute) 62 // NOTE: requiring __cplusplus above should not be necessary, but 63 // works around https://bugs.llvm.org/show_bug.cgi?id=23435. 64 #define ABSL_HAVE_CPP_ATTRIBUTE(x) __has_cpp_attribute(x) 65 #else 66 #define ABSL_HAVE_CPP_ATTRIBUTE(x) 0 67 #endif 68 69 // ----------------------------------------------------------------------------- 70 // Function Attributes 71 // ----------------------------------------------------------------------------- 72 // 73 // GCC: https://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html 74 // Clang: https://clang.llvm.org/docs/AttributeReference.html 75 76 // ABSL_PRINTF_ATTRIBUTE 77 // ABSL_SCANF_ATTRIBUTE 78 // 79 // Tells the compiler to perform `printf` format string checking if the 80 // compiler supports it; see the 'format' attribute in 81 // <https://gcc.gnu.org/onlinedocs/gcc-4.7.0/gcc/Function-Attributes.html>. 82 // 83 // Note: As the GCC manual states, "[s]ince non-static C++ methods 84 // have an implicit 'this' argument, the arguments of such methods 85 // should be counted from two, not one." 86 #if ABSL_HAVE_ATTRIBUTE(format) || (defined(__GNUC__) && !defined(__clang__)) 87 #define ABSL_PRINTF_ATTRIBUTE(string_index, first_to_check) \ 88 __attribute__((__format__(__printf__, string_index, first_to_check))) 89 #define ABSL_SCANF_ATTRIBUTE(string_index, first_to_check) \ 90 __attribute__((__format__(__scanf__, string_index, first_to_check))) 91 #else 92 #define ABSL_PRINTF_ATTRIBUTE(string_index, first_to_check) 93 #define ABSL_SCANF_ATTRIBUTE(string_index, first_to_check) 94 #endif 95 96 // ABSL_ATTRIBUTE_ALWAYS_INLINE 97 // ABSL_ATTRIBUTE_NOINLINE 98 // 99 // Forces functions to either inline or not inline. Introduced in gcc 3.1. 100 #if ABSL_HAVE_ATTRIBUTE(always_inline) || \ 101 (defined(__GNUC__) && !defined(__clang__)) 102 #define ABSL_ATTRIBUTE_ALWAYS_INLINE __attribute__((always_inline)) 103 #define ABSL_HAVE_ATTRIBUTE_ALWAYS_INLINE 1 104 #else 105 #define ABSL_ATTRIBUTE_ALWAYS_INLINE 106 #endif 107 108 #if ABSL_HAVE_ATTRIBUTE(noinline) || (defined(__GNUC__) && !defined(__clang__)) 109 #define ABSL_ATTRIBUTE_NOINLINE __attribute__((noinline)) 110 #define ABSL_HAVE_ATTRIBUTE_NOINLINE 1 111 #else 112 #define ABSL_ATTRIBUTE_NOINLINE 113 #endif 114 115 // ABSL_ATTRIBUTE_NO_TAIL_CALL 116 // 117 // Prevents the compiler from optimizing away stack frames for functions which 118 // end in a call to another function. 119 #if ABSL_HAVE_ATTRIBUTE(disable_tail_calls) 120 #define ABSL_HAVE_ATTRIBUTE_NO_TAIL_CALL 1 121 #define ABSL_ATTRIBUTE_NO_TAIL_CALL __attribute__((disable_tail_calls)) 122 #elif defined(__GNUC__) && !defined(__clang__) && !defined(__e2k__) 123 #define ABSL_HAVE_ATTRIBUTE_NO_TAIL_CALL 1 124 #define ABSL_ATTRIBUTE_NO_TAIL_CALL \ 125 __attribute__((optimize("no-optimize-sibling-calls"))) 126 #else 127 #define ABSL_ATTRIBUTE_NO_TAIL_CALL 128 #define ABSL_HAVE_ATTRIBUTE_NO_TAIL_CALL 0 129 #endif 130 131 // ABSL_ATTRIBUTE_WEAK 132 // 133 // Tags a function as weak for the purposes of compilation and linking. 134 // Weak attributes did not work properly in LLVM's Windows backend before 135 // 9.0.0, so disable them there. See https://bugs.llvm.org/show_bug.cgi?id=37598 136 // for further information. 137 // The MinGW compiler doesn't complain about the weak attribute until the link 138 // step, presumably because Windows doesn't use ELF binaries. 139 #if (ABSL_HAVE_ATTRIBUTE(weak) || \ 140 (defined(__GNUC__) && !defined(__clang__))) && \ 141 (!defined(_WIN32) || __clang_major__ < 9) && !defined(__MINGW32__) 142 #undef ABSL_ATTRIBUTE_WEAK 143 #define ABSL_ATTRIBUTE_WEAK __attribute__((weak)) 144 #define ABSL_HAVE_ATTRIBUTE_WEAK 1 145 #else 146 #define ABSL_ATTRIBUTE_WEAK 147 #define ABSL_HAVE_ATTRIBUTE_WEAK 0 148 #endif 149 150 // ABSL_ATTRIBUTE_NONNULL 151 // 152 // Tells the compiler either (a) that a particular function parameter 153 // should be a non-null pointer, or (b) that all pointer arguments should 154 // be non-null. 155 // 156 // Note: As the GCC manual states, "[s]ince non-static C++ methods 157 // have an implicit 'this' argument, the arguments of such methods 158 // should be counted from two, not one." 159 // 160 // Args are indexed starting at 1. 161 // 162 // For non-static class member functions, the implicit `this` argument 163 // is arg 1, and the first explicit argument is arg 2. For static class member 164 // functions, there is no implicit `this`, and the first explicit argument is 165 // arg 1. 166 // 167 // Example: 168 // 169 // /* arg_a cannot be null, but arg_b can */ 170 // void Function(void* arg_a, void* arg_b) ABSL_ATTRIBUTE_NONNULL(1); 171 // 172 // class C { 173 // /* arg_a cannot be null, but arg_b can */ 174 // void Method(void* arg_a, void* arg_b) ABSL_ATTRIBUTE_NONNULL(2); 175 // 176 // /* arg_a cannot be null, but arg_b can */ 177 // static void StaticMethod(void* arg_a, void* arg_b) 178 // ABSL_ATTRIBUTE_NONNULL(1); 179 // }; 180 // 181 // If no arguments are provided, then all pointer arguments should be non-null. 182 // 183 // /* No pointer arguments may be null. */ 184 // void Function(void* arg_a, void* arg_b, int arg_c) ABSL_ATTRIBUTE_NONNULL(); 185 // 186 // NOTE: The GCC nonnull attribute actually accepts a list of arguments, but 187 // ABSL_ATTRIBUTE_NONNULL does not. 188 #if ABSL_HAVE_ATTRIBUTE(nonnull) || (defined(__GNUC__) && !defined(__clang__)) 189 #define ABSL_ATTRIBUTE_NONNULL(arg_index) __attribute__((nonnull(arg_index))) 190 #else 191 #define ABSL_ATTRIBUTE_NONNULL(...) 192 #endif 193 194 // ABSL_ATTRIBUTE_NORETURN 195 // 196 // Tells the compiler that a given function never returns. 197 #if ABSL_HAVE_ATTRIBUTE(noreturn) || (defined(__GNUC__) && !defined(__clang__)) 198 #define ABSL_ATTRIBUTE_NORETURN __attribute__((noreturn)) 199 #elif defined(_MSC_VER) 200 #define ABSL_ATTRIBUTE_NORETURN __declspec(noreturn) 201 #else 202 #define ABSL_ATTRIBUTE_NORETURN 203 #endif 204 205 // ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS 206 // 207 // Tells the AddressSanitizer (or other memory testing tools) to ignore a given 208 // function. Useful for cases when a function reads random locations on stack, 209 // calls _exit from a cloned subprocess, deliberately accesses buffer 210 // out of bounds or does other scary things with memory. 211 // NOTE: GCC supports AddressSanitizer(asan) since 4.8. 212 // https://gcc.gnu.org/gcc-4.8/changes.html 213 #if ABSL_HAVE_ATTRIBUTE(no_sanitize_address) 214 #define ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS __attribute__((no_sanitize_address)) 215 #else 216 #define ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS 217 #endif 218 219 // ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY 220 // 221 // Tells the MemorySanitizer to relax the handling of a given function. All "Use 222 // of uninitialized value" warnings from such functions will be suppressed, and 223 // all values loaded from memory will be considered fully initialized. This 224 // attribute is similar to the ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS attribute 225 // above, but deals with initialized-ness rather than addressability issues. 226 // NOTE: MemorySanitizer(msan) is supported by Clang but not GCC. 227 #if ABSL_HAVE_ATTRIBUTE(no_sanitize_memory) 228 #define ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY __attribute__((no_sanitize_memory)) 229 #else 230 #define ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY 231 #endif 232 233 // ABSL_ATTRIBUTE_NO_SANITIZE_THREAD 234 // 235 // Tells the ThreadSanitizer to not instrument a given function. 236 // NOTE: GCC supports ThreadSanitizer(tsan) since 4.8. 237 // https://gcc.gnu.org/gcc-4.8/changes.html 238 #if ABSL_HAVE_ATTRIBUTE(no_sanitize_thread) 239 #define ABSL_ATTRIBUTE_NO_SANITIZE_THREAD __attribute__((no_sanitize_thread)) 240 #else 241 #define ABSL_ATTRIBUTE_NO_SANITIZE_THREAD 242 #endif 243 244 // ABSL_ATTRIBUTE_NO_SANITIZE_UNDEFINED 245 // 246 // Tells the UndefinedSanitizer to ignore a given function. Useful for cases 247 // where certain behavior (eg. division by zero) is being used intentionally. 248 // NOTE: GCC supports UndefinedBehaviorSanitizer(ubsan) since 4.9. 249 // https://gcc.gnu.org/gcc-4.9/changes.html 250 #if ABSL_HAVE_ATTRIBUTE(no_sanitize_undefined) 251 #define ABSL_ATTRIBUTE_NO_SANITIZE_UNDEFINED \ 252 __attribute__((no_sanitize_undefined)) 253 #elif ABSL_HAVE_ATTRIBUTE(no_sanitize) 254 #define ABSL_ATTRIBUTE_NO_SANITIZE_UNDEFINED \ 255 __attribute__((no_sanitize("undefined"))) 256 #else 257 #define ABSL_ATTRIBUTE_NO_SANITIZE_UNDEFINED 258 #endif 259 260 // ABSL_ATTRIBUTE_NO_SANITIZE_CFI 261 // 262 // Tells the ControlFlowIntegrity sanitizer to not instrument a given function. 263 // See https://clang.llvm.org/docs/ControlFlowIntegrity.html for details. 264 #if ABSL_HAVE_ATTRIBUTE(no_sanitize) 265 #define ABSL_ATTRIBUTE_NO_SANITIZE_CFI __attribute__((no_sanitize("cfi"))) 266 #else 267 #define ABSL_ATTRIBUTE_NO_SANITIZE_CFI 268 #endif 269 270 // ABSL_ATTRIBUTE_NO_SANITIZE_SAFESTACK 271 // 272 // Tells the SafeStack to not instrument a given function. 273 // See https://clang.llvm.org/docs/SafeStack.html for details. 274 #if ABSL_HAVE_ATTRIBUTE(no_sanitize) 275 #define ABSL_ATTRIBUTE_NO_SANITIZE_SAFESTACK \ 276 __attribute__((no_sanitize("safe-stack"))) 277 #else 278 #define ABSL_ATTRIBUTE_NO_SANITIZE_SAFESTACK 279 #endif 280 281 // ABSL_ATTRIBUTE_RETURNS_NONNULL 282 // 283 // Tells the compiler that a particular function never returns a null pointer. 284 #if ABSL_HAVE_ATTRIBUTE(returns_nonnull) 285 #define ABSL_ATTRIBUTE_RETURNS_NONNULL __attribute__((returns_nonnull)) 286 #else 287 #define ABSL_ATTRIBUTE_RETURNS_NONNULL 288 #endif 289 290 // ABSL_HAVE_ATTRIBUTE_SECTION 291 // 292 // Indicates whether labeled sections are supported. Weak symbol support is 293 // a prerequisite. Labeled sections are not supported on Darwin/iOS. 294 #ifdef ABSL_HAVE_ATTRIBUTE_SECTION 295 #error ABSL_HAVE_ATTRIBUTE_SECTION cannot be directly set 296 #elif (ABSL_HAVE_ATTRIBUTE(section) || \ 297 (defined(__GNUC__) && !defined(__clang__))) && \ 298 !defined(__APPLE__) && ABSL_HAVE_ATTRIBUTE_WEAK 299 #define ABSL_HAVE_ATTRIBUTE_SECTION 1 300 301 // ABSL_ATTRIBUTE_SECTION 302 // 303 // Tells the compiler/linker to put a given function into a section and define 304 // `__start_ ## name` and `__stop_ ## name` symbols to bracket the section. 305 // This functionality is supported by GNU linker. Any function annotated with 306 // `ABSL_ATTRIBUTE_SECTION` must not be inlined, or it will be placed into 307 // whatever section its caller is placed into. 308 // 309 #ifndef ABSL_ATTRIBUTE_SECTION 310 #define ABSL_ATTRIBUTE_SECTION(name) \ 311 __attribute__((section(#name))) __attribute__((noinline)) 312 #endif 313 314 315 // ABSL_ATTRIBUTE_SECTION_VARIABLE 316 // 317 // Tells the compiler/linker to put a given variable into a section and define 318 // `__start_ ## name` and `__stop_ ## name` symbols to bracket the section. 319 // This functionality is supported by GNU linker. 320 #ifndef ABSL_ATTRIBUTE_SECTION_VARIABLE 321 #ifdef _AIX 322 // __attribute__((section(#name))) on AIX is achived by using the `.csect` psudo 323 // op which includes an additional integer as part of its syntax indcating 324 // alignment. If data fall under different alignments then you might get a 325 // compilation error indicating a `Section type conflict`. 326 #define ABSL_ATTRIBUTE_SECTION_VARIABLE(name) 327 #else 328 #define ABSL_ATTRIBUTE_SECTION_VARIABLE(name) __attribute__((section(#name))) 329 #endif 330 #endif 331 332 // ABSL_DECLARE_ATTRIBUTE_SECTION_VARS 333 // 334 // A weak section declaration to be used as a global declaration 335 // for ABSL_ATTRIBUTE_SECTION_START|STOP(name) to compile and link 336 // even without functions with ABSL_ATTRIBUTE_SECTION(name). 337 // ABSL_DEFINE_ATTRIBUTE_SECTION should be in the exactly one file; it's 338 // a no-op on ELF but not on Mach-O. 339 // 340 #ifndef ABSL_DECLARE_ATTRIBUTE_SECTION_VARS 341 #define ABSL_DECLARE_ATTRIBUTE_SECTION_VARS(name) \ 342 extern char __start_##name[] ABSL_ATTRIBUTE_WEAK; \ 343 extern char __stop_##name[] ABSL_ATTRIBUTE_WEAK 344 #endif 345 #ifndef ABSL_DEFINE_ATTRIBUTE_SECTION_VARS 346 #define ABSL_INIT_ATTRIBUTE_SECTION_VARS(name) 347 #define ABSL_DEFINE_ATTRIBUTE_SECTION_VARS(name) 348 #endif 349 350 // ABSL_ATTRIBUTE_SECTION_START 351 // 352 // Returns `void*` pointers to start/end of a section of code with 353 // functions having ABSL_ATTRIBUTE_SECTION(name). 354 // Returns 0 if no such functions exist. 355 // One must ABSL_DECLARE_ATTRIBUTE_SECTION_VARS(name) for this to compile and 356 // link. 357 // 358 #define ABSL_ATTRIBUTE_SECTION_START(name) \ 359 (reinterpret_cast<void *>(__start_##name)) 360 #define ABSL_ATTRIBUTE_SECTION_STOP(name) \ 361 (reinterpret_cast<void *>(__stop_##name)) 362 363 #else // !ABSL_HAVE_ATTRIBUTE_SECTION 364 365 #define ABSL_HAVE_ATTRIBUTE_SECTION 0 366 367 // provide dummy definitions 368 #define ABSL_ATTRIBUTE_SECTION(name) 369 #define ABSL_ATTRIBUTE_SECTION_VARIABLE(name) 370 #define ABSL_INIT_ATTRIBUTE_SECTION_VARS(name) 371 #define ABSL_DEFINE_ATTRIBUTE_SECTION_VARS(name) 372 #define ABSL_DECLARE_ATTRIBUTE_SECTION_VARS(name) 373 #define ABSL_ATTRIBUTE_SECTION_START(name) (reinterpret_cast<void *>(0)) 374 #define ABSL_ATTRIBUTE_SECTION_STOP(name) (reinterpret_cast<void *>(0)) 375 376 #endif // ABSL_ATTRIBUTE_SECTION 377 378 // ABSL_ATTRIBUTE_STACK_ALIGN_FOR_OLD_LIBC 379 // 380 // Support for aligning the stack on 32-bit x86. 381 #if ABSL_HAVE_ATTRIBUTE(force_align_arg_pointer) || \ 382 (defined(__GNUC__) && !defined(__clang__)) 383 #if defined(__i386__) 384 #define ABSL_ATTRIBUTE_STACK_ALIGN_FOR_OLD_LIBC \ 385 __attribute__((force_align_arg_pointer)) 386 #define ABSL_REQUIRE_STACK_ALIGN_TRAMPOLINE (0) 387 #elif defined(__x86_64__) 388 #define ABSL_REQUIRE_STACK_ALIGN_TRAMPOLINE (1) 389 #define ABSL_ATTRIBUTE_STACK_ALIGN_FOR_OLD_LIBC 390 #else // !__i386__ && !__x86_64 391 #define ABSL_REQUIRE_STACK_ALIGN_TRAMPOLINE (0) 392 #define ABSL_ATTRIBUTE_STACK_ALIGN_FOR_OLD_LIBC 393 #endif // __i386__ 394 #else 395 #define ABSL_ATTRIBUTE_STACK_ALIGN_FOR_OLD_LIBC 396 #define ABSL_REQUIRE_STACK_ALIGN_TRAMPOLINE (0) 397 #endif 398 399 // ABSL_MUST_USE_RESULT 400 // 401 // Tells the compiler to warn about unused results. 402 // 403 // When annotating a function, it must appear as the first part of the 404 // declaration or definition. The compiler will warn if the return value from 405 // such a function is unused: 406 // 407 // ABSL_MUST_USE_RESULT Sprocket* AllocateSprocket(); 408 // AllocateSprocket(); // Triggers a warning. 409 // 410 // When annotating a class, it is equivalent to annotating every function which 411 // returns an instance. 412 // 413 // class ABSL_MUST_USE_RESULT Sprocket {}; 414 // Sprocket(); // Triggers a warning. 415 // 416 // Sprocket MakeSprocket(); 417 // MakeSprocket(); // Triggers a warning. 418 // 419 // Note that references and pointers are not instances: 420 // 421 // Sprocket* SprocketPointer(); 422 // SprocketPointer(); // Does *not* trigger a warning. 423 // 424 // ABSL_MUST_USE_RESULT allows using cast-to-void to suppress the unused result 425 // warning. For that, warn_unused_result is used only for clang but not for gcc. 426 // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66425 427 // 428 // Note: past advice was to place the macro after the argument list. 429 #if ABSL_HAVE_ATTRIBUTE(nodiscard) 430 #define ABSL_MUST_USE_RESULT [[nodiscard]] 431 #elif defined(__clang__) && ABSL_HAVE_ATTRIBUTE(warn_unused_result) 432 #define ABSL_MUST_USE_RESULT __attribute__((warn_unused_result)) 433 #else 434 #define ABSL_MUST_USE_RESULT 435 #endif 436 437 // ABSL_ATTRIBUTE_HOT, ABSL_ATTRIBUTE_COLD 438 // 439 // Tells GCC that a function is hot or cold. GCC can use this information to 440 // improve static analysis, i.e. a conditional branch to a cold function 441 // is likely to be not-taken. 442 // This annotation is used for function declarations. 443 // 444 // Example: 445 // 446 // int foo() ABSL_ATTRIBUTE_HOT; 447 #if ABSL_HAVE_ATTRIBUTE(hot) || (defined(__GNUC__) && !defined(__clang__)) 448 #define ABSL_ATTRIBUTE_HOT __attribute__((hot)) 449 #else 450 #define ABSL_ATTRIBUTE_HOT 451 #endif 452 453 #if ABSL_HAVE_ATTRIBUTE(cold) || (defined(__GNUC__) && !defined(__clang__)) 454 #define ABSL_ATTRIBUTE_COLD __attribute__((cold)) 455 #else 456 #define ABSL_ATTRIBUTE_COLD 457 #endif 458 459 // ABSL_XRAY_ALWAYS_INSTRUMENT, ABSL_XRAY_NEVER_INSTRUMENT, ABSL_XRAY_LOG_ARGS 460 // 461 // We define the ABSL_XRAY_ALWAYS_INSTRUMENT and ABSL_XRAY_NEVER_INSTRUMENT 462 // macro used as an attribute to mark functions that must always or never be 463 // instrumented by XRay. Currently, this is only supported in Clang/LLVM. 464 // 465 // For reference on the LLVM XRay instrumentation, see 466 // http://llvm.org/docs/XRay.html. 467 // 468 // A function with the XRAY_ALWAYS_INSTRUMENT macro attribute in its declaration 469 // will always get the XRay instrumentation sleds. These sleds may introduce 470 // some binary size and runtime overhead and must be used sparingly. 471 // 472 // These attributes only take effect when the following conditions are met: 473 // 474 // * The file/target is built in at least C++11 mode, with a Clang compiler 475 // that supports XRay attributes. 476 // * The file/target is built with the -fxray-instrument flag set for the 477 // Clang/LLVM compiler. 478 // * The function is defined in the translation unit (the compiler honors the 479 // attribute in either the definition or the declaration, and must match). 480 // 481 // There are cases when, even when building with XRay instrumentation, users 482 // might want to control specifically which functions are instrumented for a 483 // particular build using special-case lists provided to the compiler. These 484 // special case lists are provided to Clang via the 485 // -fxray-always-instrument=... and -fxray-never-instrument=... flags. The 486 // attributes in source take precedence over these special-case lists. 487 // 488 // To disable the XRay attributes at build-time, users may define 489 // ABSL_NO_XRAY_ATTRIBUTES. Do NOT define ABSL_NO_XRAY_ATTRIBUTES on specific 490 // packages/targets, as this may lead to conflicting definitions of functions at 491 // link-time. 492 // 493 // XRay isn't currently supported on Android: 494 // https://github.com/android/ndk/issues/368 495 #if ABSL_HAVE_CPP_ATTRIBUTE(clang::xray_always_instrument) && \ 496 !defined(ABSL_NO_XRAY_ATTRIBUTES) && !defined(__ANDROID__) 497 #define ABSL_XRAY_ALWAYS_INSTRUMENT [[clang::xray_always_instrument]] 498 #define ABSL_XRAY_NEVER_INSTRUMENT [[clang::xray_never_instrument]] 499 #if ABSL_HAVE_CPP_ATTRIBUTE(clang::xray_log_args) 500 #define ABSL_XRAY_LOG_ARGS(N) \ 501 [[clang::xray_always_instrument, clang::xray_log_args(N)]] 502 #else 503 #define ABSL_XRAY_LOG_ARGS(N) [[clang::xray_always_instrument]] 504 #endif 505 #else 506 #define ABSL_XRAY_ALWAYS_INSTRUMENT 507 #define ABSL_XRAY_NEVER_INSTRUMENT 508 #define ABSL_XRAY_LOG_ARGS(N) 509 #endif 510 511 // ABSL_ATTRIBUTE_REINITIALIZES 512 // 513 // Indicates that a member function reinitializes the entire object to a known 514 // state, independent of the previous state of the object. 515 // 516 // The clang-tidy check bugprone-use-after-move allows member functions marked 517 // with this attribute to be called on objects that have been moved from; 518 // without the attribute, this would result in a use-after-move warning. 519 #if ABSL_HAVE_CPP_ATTRIBUTE(clang::reinitializes) 520 #define ABSL_ATTRIBUTE_REINITIALIZES [[clang::reinitializes]] 521 #else 522 #define ABSL_ATTRIBUTE_REINITIALIZES 523 #endif 524 525 // ----------------------------------------------------------------------------- 526 // Variable Attributes 527 // ----------------------------------------------------------------------------- 528 529 // ABSL_ATTRIBUTE_UNUSED 530 // 531 // Prevents the compiler from complaining about variables that appear unused. 532 // 533 // For code or headers that are assured to only build with C++17 and up, prefer 534 // just using the standard '[[maybe_unused]]' directly over this macro. 535 // 536 // Due to differences in positioning requirements between the old, compiler 537 // specific __attribute__ syntax and the now standard [[maybe_unused]], this 538 // macro does not attempt to take advantage of '[[maybe_unused]]'. 539 #if ABSL_HAVE_ATTRIBUTE(unused) || (defined(__GNUC__) && !defined(__clang__)) 540 #undef ABSL_ATTRIBUTE_UNUSED 541 #define ABSL_ATTRIBUTE_UNUSED __attribute__((__unused__)) 542 #else 543 #define ABSL_ATTRIBUTE_UNUSED 544 #endif 545 546 // ABSL_ATTRIBUTE_INITIAL_EXEC 547 // 548 // Tells the compiler to use "initial-exec" mode for a thread-local variable. 549 // See http://people.redhat.com/drepper/tls.pdf for the gory details. 550 #if ABSL_HAVE_ATTRIBUTE(tls_model) || (defined(__GNUC__) && !defined(__clang__)) 551 #define ABSL_ATTRIBUTE_INITIAL_EXEC __attribute__((tls_model("initial-exec"))) 552 #else 553 #define ABSL_ATTRIBUTE_INITIAL_EXEC 554 #endif 555 556 // ABSL_ATTRIBUTE_PACKED 557 // 558 // Instructs the compiler not to use natural alignment for a tagged data 559 // structure, but instead to reduce its alignment to 1. 560 // 561 // Therefore, DO NOT APPLY THIS ATTRIBUTE TO STRUCTS CONTAINING ATOMICS. Doing 562 // so can cause atomic variables to be mis-aligned and silently violate 563 // atomicity on x86. 564 // 565 // This attribute can either be applied to members of a structure or to a 566 // structure in its entirety. Applying this attribute (judiciously) to a 567 // structure in its entirety to optimize the memory footprint of very 568 // commonly-used structs is fine. Do not apply this attribute to a structure in 569 // its entirety if the purpose is to control the offsets of the members in the 570 // structure. Instead, apply this attribute only to structure members that need 571 // it. 572 // 573 // When applying ABSL_ATTRIBUTE_PACKED only to specific structure members the 574 // natural alignment of structure members not annotated is preserved. Aligned 575 // member accesses are faster than non-aligned member accesses even if the 576 // targeted microprocessor supports non-aligned accesses. 577 #if ABSL_HAVE_ATTRIBUTE(packed) || (defined(__GNUC__) && !defined(__clang__)) 578 #define ABSL_ATTRIBUTE_PACKED __attribute__((__packed__)) 579 #else 580 #define ABSL_ATTRIBUTE_PACKED 581 #endif 582 583 // ABSL_ATTRIBUTE_FUNC_ALIGN 584 // 585 // Tells the compiler to align the function start at least to certain 586 // alignment boundary 587 #if ABSL_HAVE_ATTRIBUTE(aligned) || (defined(__GNUC__) && !defined(__clang__)) 588 #define ABSL_ATTRIBUTE_FUNC_ALIGN(bytes) __attribute__((aligned(bytes))) 589 #else 590 #define ABSL_ATTRIBUTE_FUNC_ALIGN(bytes) 591 #endif 592 593 // ABSL_FALLTHROUGH_INTENDED 594 // 595 // Annotates implicit fall-through between switch labels, allowing a case to 596 // indicate intentional fallthrough and turn off warnings about any lack of a 597 // `break` statement. The ABSL_FALLTHROUGH_INTENDED macro should be followed by 598 // a semicolon and can be used in most places where `break` can, provided that 599 // no statements exist between it and the next switch label. 600 // 601 // Example: 602 // 603 // switch (x) { 604 // case 40: 605 // case 41: 606 // if (truth_is_out_there) { 607 // ++x; 608 // ABSL_FALLTHROUGH_INTENDED; // Use instead of/along with annotations 609 // // in comments 610 // } else { 611 // return x; 612 // } 613 // case 42: 614 // ... 615 // 616 // Notes: When supported, GCC and Clang can issue a warning on switch labels 617 // with unannotated fallthrough using the warning `-Wimplicit-fallthrough`. See 618 // clang documentation on language extensions for details: 619 // https://clang.llvm.org/docs/AttributeReference.html#fallthrough-clang-fallthrough 620 // 621 // When used with unsupported compilers, the ABSL_FALLTHROUGH_INTENDED macro has 622 // no effect on diagnostics. In any case this macro has no effect on runtime 623 // behavior and performance of code. 624 625 #ifdef ABSL_FALLTHROUGH_INTENDED 626 #error "ABSL_FALLTHROUGH_INTENDED should not be defined." 627 #elif ABSL_HAVE_CPP_ATTRIBUTE(fallthrough) 628 #define ABSL_FALLTHROUGH_INTENDED [[fallthrough]] 629 #elif ABSL_HAVE_CPP_ATTRIBUTE(clang::fallthrough) 630 #define ABSL_FALLTHROUGH_INTENDED [[clang::fallthrough]] 631 #elif ABSL_HAVE_CPP_ATTRIBUTE(gnu::fallthrough) 632 #define ABSL_FALLTHROUGH_INTENDED [[gnu::fallthrough]] 633 #else 634 #define ABSL_FALLTHROUGH_INTENDED \ 635 do { \ 636 } while (0) 637 #endif 638 639 // ABSL_DEPRECATED() 640 // 641 // Marks a deprecated class, struct, enum, function, method and variable 642 // declarations. The macro argument is used as a custom diagnostic message (e.g. 643 // suggestion of a better alternative). 644 // 645 // Examples: 646 // 647 // class ABSL_DEPRECATED("Use Bar instead") Foo {...}; 648 // 649 // ABSL_DEPRECATED("Use Baz() instead") void Bar() {...} 650 // 651 // template <typename T> 652 // ABSL_DEPRECATED("Use DoThat() instead") 653 // void DoThis(); 654 // 655 // Every usage of a deprecated entity will trigger a warning when compiled with 656 // clang's `-Wdeprecated-declarations` option. This option is turned off by 657 // default, but the warnings will be reported by clang-tidy. 658 #if defined(__clang__) && defined(__cplusplus) && __cplusplus >= 201103L 659 #define ABSL_DEPRECATED(message) __attribute__((deprecated(message))) 660 #endif 661 662 #ifndef ABSL_DEPRECATED 663 #define ABSL_DEPRECATED(message) 664 #endif 665 666 // ABSL_CONST_INIT 667 // 668 // A variable declaration annotated with the `ABSL_CONST_INIT` attribute will 669 // not compile (on supported platforms) unless the variable has a constant 670 // initializer. This is useful for variables with static and thread storage 671 // duration, because it guarantees that they will not suffer from the so-called 672 // "static init order fiasco". Prefer to put this attribute on the most visible 673 // declaration of the variable, if there's more than one, because code that 674 // accesses the variable can then use the attribute for optimization. 675 // 676 // Example: 677 // 678 // class MyClass { 679 // public: 680 // ABSL_CONST_INIT static MyType my_var; 681 // }; 682 // 683 // MyType MyClass::my_var = MakeMyType(...); 684 // 685 // Note that this attribute is redundant if the variable is declared constexpr. 686 #if ABSL_HAVE_CPP_ATTRIBUTE(clang::require_constant_initialization) 687 #define ABSL_CONST_INIT [[clang::require_constant_initialization]] 688 #else 689 #define ABSL_CONST_INIT 690 #endif // ABSL_HAVE_CPP_ATTRIBUTE(clang::require_constant_initialization) 691 692 // ABSL_ATTRIBUTE_PURE_FUNCTION 693 // 694 // ABSL_ATTRIBUTE_PURE_FUNCTION is used to annotate declarations of "pure" 695 // functions. A function is pure if its return value is only a function of its 696 // arguments. The pure attribute prohibits a function from modifying the state 697 // of the program that is observable by means other than inspecting the 698 // function's return value. Declaring such functions with the pure attribute 699 // allows the compiler to avoid emitting some calls in repeated invocations of 700 // the function with the same argument values. 701 // 702 // Example: 703 // 704 // ABSL_ATTRIBUTE_PURE_FUNCTION int64_t ToInt64Milliseconds(Duration d); 705 #if ABSL_HAVE_CPP_ATTRIBUTE(gnu::pure) 706 #define ABSL_ATTRIBUTE_PURE_FUNCTION [[gnu::pure]] 707 #elif ABSL_HAVE_ATTRIBUTE(pure) 708 #define ABSL_ATTRIBUTE_PURE_FUNCTION __attribute__((pure)) 709 #else 710 #define ABSL_ATTRIBUTE_PURE_FUNCTION 711 #endif 712 713 // ABSL_ATTRIBUTE_LIFETIME_BOUND indicates that a resource owned by a function 714 // parameter or implicit object parameter is retained by the return value of the 715 // annotated function (or, for a parameter of a constructor, in the value of the 716 // constructed object). This attribute causes warnings to be produced if a 717 // temporary object does not live long enough. 718 // 719 // When applied to a reference parameter, the referenced object is assumed to be 720 // retained by the return value of the function. When applied to a non-reference 721 // parameter (for example, a pointer or a class type), all temporaries 722 // referenced by the parameter are assumed to be retained by the return value of 723 // the function. 724 // 725 // See also the upstream documentation: 726 // https://clang.llvm.org/docs/AttributeReference.html#lifetimebound 727 #if ABSL_HAVE_CPP_ATTRIBUTE(clang::lifetimebound) 728 #define ABSL_ATTRIBUTE_LIFETIME_BOUND [[clang::lifetimebound]] 729 #elif ABSL_HAVE_ATTRIBUTE(lifetimebound) 730 #define ABSL_ATTRIBUTE_LIFETIME_BOUND __attribute__((lifetimebound)) 731 #else 732 #define ABSL_ATTRIBUTE_LIFETIME_BOUND 733 #endif 734 735 #endif // ABSL_BASE_ATTRIBUTES_H_ 736