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) || (defined(__clang__) && __clang_major__ >= 9)) && \ 142 !defined(__MINGW32__) 143 #undef ABSL_ATTRIBUTE_WEAK 144 #define ABSL_ATTRIBUTE_WEAK __attribute__((weak)) 145 #define ABSL_HAVE_ATTRIBUTE_WEAK 1 146 #else 147 #define ABSL_ATTRIBUTE_WEAK 148 #define ABSL_HAVE_ATTRIBUTE_WEAK 0 149 #endif 150 151 // ABSL_ATTRIBUTE_NONNULL 152 // 153 // Tells the compiler either (a) that a particular function parameter 154 // should be a non-null pointer, or (b) that all pointer arguments should 155 // be non-null. 156 // 157 // Note: As the GCC manual states, "[s]ince non-static C++ methods 158 // have an implicit 'this' argument, the arguments of such methods 159 // should be counted from two, not one." 160 // 161 // Args are indexed starting at 1. 162 // 163 // For non-static class member functions, the implicit `this` argument 164 // is arg 1, and the first explicit argument is arg 2. For static class member 165 // functions, there is no implicit `this`, and the first explicit argument is 166 // arg 1. 167 // 168 // Example: 169 // 170 // /* arg_a cannot be null, but arg_b can */ 171 // void Function(void* arg_a, void* arg_b) ABSL_ATTRIBUTE_NONNULL(1); 172 // 173 // class C { 174 // /* arg_a cannot be null, but arg_b can */ 175 // void Method(void* arg_a, void* arg_b) ABSL_ATTRIBUTE_NONNULL(2); 176 // 177 // /* arg_a cannot be null, but arg_b can */ 178 // static void StaticMethod(void* arg_a, void* arg_b) 179 // ABSL_ATTRIBUTE_NONNULL(1); 180 // }; 181 // 182 // If no arguments are provided, then all pointer arguments should be non-null. 183 // 184 // /* No pointer arguments may be null. */ 185 // void Function(void* arg_a, void* arg_b, int arg_c) ABSL_ATTRIBUTE_NONNULL(); 186 // 187 // NOTE: The GCC nonnull attribute actually accepts a list of arguments, but 188 // ABSL_ATTRIBUTE_NONNULL does not. 189 #if ABSL_HAVE_ATTRIBUTE(nonnull) || (defined(__GNUC__) && !defined(__clang__)) 190 #define ABSL_ATTRIBUTE_NONNULL(arg_index) __attribute__((nonnull(arg_index))) 191 #else 192 #define ABSL_ATTRIBUTE_NONNULL(...) 193 #endif 194 195 // ABSL_ATTRIBUTE_NORETURN 196 // 197 // Tells the compiler that a given function never returns. 198 #if ABSL_HAVE_ATTRIBUTE(noreturn) || (defined(__GNUC__) && !defined(__clang__)) 199 #define ABSL_ATTRIBUTE_NORETURN __attribute__((noreturn)) 200 #elif defined(_MSC_VER) 201 #define ABSL_ATTRIBUTE_NORETURN __declspec(noreturn) 202 #else 203 #define ABSL_ATTRIBUTE_NORETURN 204 #endif 205 206 // ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS 207 // 208 // Tells the AddressSanitizer (or other memory testing tools) to ignore a given 209 // function. Useful for cases when a function reads random locations on stack, 210 // calls _exit from a cloned subprocess, deliberately accesses buffer 211 // out of bounds or does other scary things with memory. 212 // NOTE: GCC supports AddressSanitizer(asan) since 4.8. 213 // https://gcc.gnu.org/gcc-4.8/changes.html 214 #if defined(ABSL_HAVE_ADDRESS_SANITIZER) && \ 215 ABSL_HAVE_ATTRIBUTE(no_sanitize_address) 216 #define ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS __attribute__((no_sanitize_address)) 217 #elif defined(ABSL_HAVE_ADDRESS_SANITIZER) && defined(_MSC_VER) && \ 218 _MSC_VER >= 1928 219 // https://docs.microsoft.com/en-us/cpp/cpp/no-sanitize-address 220 #define ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS __declspec(no_sanitize_address) 221 #elif defined(ABSL_HAVE_HWADDRESS_SANITIZER) && ABSL_HAVE_ATTRIBUTE(no_sanitize) 222 // HWAddressSanitizer is a sanitizer similar to AddressSanitizer, which uses CPU 223 // features to detect similar bugs with less CPU and memory overhead. 224 // NOTE: GCC supports HWAddressSanitizer(hwasan) since 11. 225 // https://gcc.gnu.org/gcc-11/changes.html 226 #define ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS \ 227 __attribute__((no_sanitize("hwaddress"))) 228 #else 229 #define ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS 230 #endif 231 232 // ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY 233 // 234 // Tells the MemorySanitizer to relax the handling of a given function. All "Use 235 // of uninitialized value" warnings from such functions will be suppressed, and 236 // all values loaded from memory will be considered fully initialized. This 237 // attribute is similar to the ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS attribute 238 // above, but deals with initialized-ness rather than addressability issues. 239 // NOTE: MemorySanitizer(msan) is supported by Clang but not GCC. 240 #if ABSL_HAVE_ATTRIBUTE(no_sanitize_memory) 241 #define ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY __attribute__((no_sanitize_memory)) 242 #else 243 #define ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY 244 #endif 245 246 // ABSL_ATTRIBUTE_NO_SANITIZE_THREAD 247 // 248 // Tells the ThreadSanitizer to not instrument a given function. 249 // NOTE: GCC supports ThreadSanitizer(tsan) since 4.8. 250 // https://gcc.gnu.org/gcc-4.8/changes.html 251 #if ABSL_HAVE_ATTRIBUTE(no_sanitize_thread) 252 #define ABSL_ATTRIBUTE_NO_SANITIZE_THREAD __attribute__((no_sanitize_thread)) 253 #else 254 #define ABSL_ATTRIBUTE_NO_SANITIZE_THREAD 255 #endif 256 257 // ABSL_ATTRIBUTE_NO_SANITIZE_UNDEFINED 258 // 259 // Tells the UndefinedSanitizer to ignore a given function. Useful for cases 260 // where certain behavior (eg. division by zero) is being used intentionally. 261 // NOTE: GCC supports UndefinedBehaviorSanitizer(ubsan) since 4.9. 262 // https://gcc.gnu.org/gcc-4.9/changes.html 263 #if ABSL_HAVE_ATTRIBUTE(no_sanitize_undefined) 264 #define ABSL_ATTRIBUTE_NO_SANITIZE_UNDEFINED \ 265 __attribute__((no_sanitize_undefined)) 266 #elif ABSL_HAVE_ATTRIBUTE(no_sanitize) 267 #define ABSL_ATTRIBUTE_NO_SANITIZE_UNDEFINED \ 268 __attribute__((no_sanitize("undefined"))) 269 #else 270 #define ABSL_ATTRIBUTE_NO_SANITIZE_UNDEFINED 271 #endif 272 273 // ABSL_ATTRIBUTE_NO_SANITIZE_CFI 274 // 275 // Tells the ControlFlowIntegrity sanitizer to not instrument a given function. 276 // See https://clang.llvm.org/docs/ControlFlowIntegrity.html for details. 277 #if ABSL_HAVE_ATTRIBUTE(no_sanitize) && defined(__llvm__) 278 #define ABSL_ATTRIBUTE_NO_SANITIZE_CFI __attribute__((no_sanitize("cfi"))) 279 #else 280 #define ABSL_ATTRIBUTE_NO_SANITIZE_CFI 281 #endif 282 283 // ABSL_ATTRIBUTE_NO_SANITIZE_SAFESTACK 284 // 285 // Tells the SafeStack to not instrument a given function. 286 // See https://clang.llvm.org/docs/SafeStack.html for details. 287 #if ABSL_HAVE_ATTRIBUTE(no_sanitize) 288 #define ABSL_ATTRIBUTE_NO_SANITIZE_SAFESTACK \ 289 __attribute__((no_sanitize("safe-stack"))) 290 #else 291 #define ABSL_ATTRIBUTE_NO_SANITIZE_SAFESTACK 292 #endif 293 294 // ABSL_ATTRIBUTE_RETURNS_NONNULL 295 // 296 // Tells the compiler that a particular function never returns a null pointer. 297 #if ABSL_HAVE_ATTRIBUTE(returns_nonnull) 298 #define ABSL_ATTRIBUTE_RETURNS_NONNULL __attribute__((returns_nonnull)) 299 #else 300 #define ABSL_ATTRIBUTE_RETURNS_NONNULL 301 #endif 302 303 // ABSL_HAVE_ATTRIBUTE_SECTION 304 // 305 // Indicates whether labeled sections are supported. Weak symbol support is 306 // a prerequisite. Labeled sections are not supported on Darwin/iOS. 307 #ifdef ABSL_HAVE_ATTRIBUTE_SECTION 308 #error ABSL_HAVE_ATTRIBUTE_SECTION cannot be directly set 309 #elif (ABSL_HAVE_ATTRIBUTE(section) || \ 310 (defined(__GNUC__) && !defined(__clang__))) && \ 311 !defined(__APPLE__) && ABSL_HAVE_ATTRIBUTE_WEAK 312 #define ABSL_HAVE_ATTRIBUTE_SECTION 1 313 314 // ABSL_ATTRIBUTE_SECTION 315 // 316 // Tells the compiler/linker to put a given function into a section and define 317 // `__start_ ## name` and `__stop_ ## name` symbols to bracket the section. 318 // This functionality is supported by GNU linker. Any function annotated with 319 // `ABSL_ATTRIBUTE_SECTION` must not be inlined, or it will be placed into 320 // whatever section its caller is placed into. 321 // 322 #ifndef ABSL_ATTRIBUTE_SECTION 323 #define ABSL_ATTRIBUTE_SECTION(name) \ 324 __attribute__((section(#name))) __attribute__((noinline)) 325 #endif 326 327 // ABSL_ATTRIBUTE_SECTION_VARIABLE 328 // 329 // Tells the compiler/linker to put a given variable into a section and define 330 // `__start_ ## name` and `__stop_ ## name` symbols to bracket the section. 331 // This functionality is supported by GNU linker. 332 #ifndef ABSL_ATTRIBUTE_SECTION_VARIABLE 333 #ifdef _AIX 334 // __attribute__((section(#name))) on AIX is achieved by using the `.csect` 335 // psudo op which includes an additional integer as part of its syntax indcating 336 // alignment. If data fall under different alignments then you might get a 337 // compilation error indicating a `Section type conflict`. 338 #define ABSL_ATTRIBUTE_SECTION_VARIABLE(name) 339 #else 340 #define ABSL_ATTRIBUTE_SECTION_VARIABLE(name) __attribute__((section(#name))) 341 #endif 342 #endif 343 344 // ABSL_DECLARE_ATTRIBUTE_SECTION_VARS 345 // 346 // A weak section declaration to be used as a global declaration 347 // for ABSL_ATTRIBUTE_SECTION_START|STOP(name) to compile and link 348 // even without functions with ABSL_ATTRIBUTE_SECTION(name). 349 // ABSL_DEFINE_ATTRIBUTE_SECTION should be in the exactly one file; it's 350 // a no-op on ELF but not on Mach-O. 351 // 352 #ifndef ABSL_DECLARE_ATTRIBUTE_SECTION_VARS 353 #define ABSL_DECLARE_ATTRIBUTE_SECTION_VARS(name) \ 354 extern char __start_##name[] ABSL_ATTRIBUTE_WEAK; \ 355 extern char __stop_##name[] ABSL_ATTRIBUTE_WEAK 356 #endif 357 #ifndef ABSL_DEFINE_ATTRIBUTE_SECTION_VARS 358 #define ABSL_INIT_ATTRIBUTE_SECTION_VARS(name) 359 #define ABSL_DEFINE_ATTRIBUTE_SECTION_VARS(name) 360 #endif 361 362 // ABSL_ATTRIBUTE_SECTION_START 363 // 364 // Returns `void*` pointers to start/end of a section of code with 365 // functions having ABSL_ATTRIBUTE_SECTION(name). 366 // Returns 0 if no such functions exist. 367 // One must ABSL_DECLARE_ATTRIBUTE_SECTION_VARS(name) for this to compile and 368 // link. 369 // 370 #define ABSL_ATTRIBUTE_SECTION_START(name) \ 371 (reinterpret_cast<void *>(__start_##name)) 372 #define ABSL_ATTRIBUTE_SECTION_STOP(name) \ 373 (reinterpret_cast<void *>(__stop_##name)) 374 375 #else // !ABSL_HAVE_ATTRIBUTE_SECTION 376 377 #define ABSL_HAVE_ATTRIBUTE_SECTION 0 378 379 // provide dummy definitions 380 #define ABSL_ATTRIBUTE_SECTION(name) 381 #define ABSL_ATTRIBUTE_SECTION_VARIABLE(name) 382 #define ABSL_INIT_ATTRIBUTE_SECTION_VARS(name) 383 #define ABSL_DEFINE_ATTRIBUTE_SECTION_VARS(name) 384 #define ABSL_DECLARE_ATTRIBUTE_SECTION_VARS(name) 385 #define ABSL_ATTRIBUTE_SECTION_START(name) (reinterpret_cast<void *>(0)) 386 #define ABSL_ATTRIBUTE_SECTION_STOP(name) (reinterpret_cast<void *>(0)) 387 388 #endif // ABSL_ATTRIBUTE_SECTION 389 390 // ABSL_ATTRIBUTE_STACK_ALIGN_FOR_OLD_LIBC 391 // 392 // Support for aligning the stack on 32-bit x86. 393 #if ABSL_HAVE_ATTRIBUTE(force_align_arg_pointer) || \ 394 (defined(__GNUC__) && !defined(__clang__)) 395 #if defined(__i386__) 396 #define ABSL_ATTRIBUTE_STACK_ALIGN_FOR_OLD_LIBC \ 397 __attribute__((force_align_arg_pointer)) 398 #define ABSL_REQUIRE_STACK_ALIGN_TRAMPOLINE (0) 399 #elif defined(__x86_64__) 400 #define ABSL_REQUIRE_STACK_ALIGN_TRAMPOLINE (1) 401 #define ABSL_ATTRIBUTE_STACK_ALIGN_FOR_OLD_LIBC 402 #else // !__i386__ && !__x86_64 403 #define ABSL_REQUIRE_STACK_ALIGN_TRAMPOLINE (0) 404 #define ABSL_ATTRIBUTE_STACK_ALIGN_FOR_OLD_LIBC 405 #endif // __i386__ 406 #else 407 #define ABSL_ATTRIBUTE_STACK_ALIGN_FOR_OLD_LIBC 408 #define ABSL_REQUIRE_STACK_ALIGN_TRAMPOLINE (0) 409 #endif 410 411 // ABSL_MUST_USE_RESULT 412 // 413 // Tells the compiler to warn about unused results. 414 // 415 // For code or headers that are assured to only build with C++17 and up, prefer 416 // just using the standard `[[nodiscard]]` directly over this macro. 417 // 418 // When annotating a function, it must appear as the first part of the 419 // declaration or definition. The compiler will warn if the return value from 420 // such a function is unused: 421 // 422 // ABSL_MUST_USE_RESULT Sprocket* AllocateSprocket(); 423 // AllocateSprocket(); // Triggers a warning. 424 // 425 // When annotating a class, it is equivalent to annotating every function which 426 // returns an instance. 427 // 428 // class ABSL_MUST_USE_RESULT Sprocket {}; 429 // Sprocket(); // Triggers a warning. 430 // 431 // Sprocket MakeSprocket(); 432 // MakeSprocket(); // Triggers a warning. 433 // 434 // Note that references and pointers are not instances: 435 // 436 // Sprocket* SprocketPointer(); 437 // SprocketPointer(); // Does *not* trigger a warning. 438 // 439 // ABSL_MUST_USE_RESULT allows using cast-to-void to suppress the unused result 440 // warning. For that, warn_unused_result is used only for clang but not for gcc. 441 // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66425 442 // 443 // Note: past advice was to place the macro after the argument list. 444 // 445 // TODO(b/176172494): Use ABSL_HAVE_CPP_ATTRIBUTE(nodiscard) when all code is 446 // compliant with the stricter [[nodiscard]]. 447 #if defined(__clang__) && ABSL_HAVE_ATTRIBUTE(warn_unused_result) 448 #define ABSL_MUST_USE_RESULT __attribute__((warn_unused_result)) 449 #else 450 #define ABSL_MUST_USE_RESULT 451 #endif 452 453 // ABSL_ATTRIBUTE_HOT, ABSL_ATTRIBUTE_COLD 454 // 455 // Tells GCC that a function is hot or cold. GCC can use this information to 456 // improve static analysis, i.e. a conditional branch to a cold function 457 // is likely to be not-taken. 458 // This annotation is used for function declarations. 459 // 460 // Example: 461 // 462 // int foo() ABSL_ATTRIBUTE_HOT; 463 #if ABSL_HAVE_ATTRIBUTE(hot) || (defined(__GNUC__) && !defined(__clang__)) 464 #define ABSL_ATTRIBUTE_HOT __attribute__((hot)) 465 #else 466 #define ABSL_ATTRIBUTE_HOT 467 #endif 468 469 #if ABSL_HAVE_ATTRIBUTE(cold) || (defined(__GNUC__) && !defined(__clang__)) 470 #define ABSL_ATTRIBUTE_COLD __attribute__((cold)) 471 #else 472 #define ABSL_ATTRIBUTE_COLD 473 #endif 474 475 // ABSL_XRAY_ALWAYS_INSTRUMENT, ABSL_XRAY_NEVER_INSTRUMENT, ABSL_XRAY_LOG_ARGS 476 // 477 // We define the ABSL_XRAY_ALWAYS_INSTRUMENT and ABSL_XRAY_NEVER_INSTRUMENT 478 // macro used as an attribute to mark functions that must always or never be 479 // instrumented by XRay. Currently, this is only supported in Clang/LLVM. 480 // 481 // For reference on the LLVM XRay instrumentation, see 482 // http://llvm.org/docs/XRay.html. 483 // 484 // A function with the XRAY_ALWAYS_INSTRUMENT macro attribute in its declaration 485 // will always get the XRay instrumentation sleds. These sleds may introduce 486 // some binary size and runtime overhead and must be used sparingly. 487 // 488 // These attributes only take effect when the following conditions are met: 489 // 490 // * The file/target is built in at least C++11 mode, with a Clang compiler 491 // that supports XRay attributes. 492 // * The file/target is built with the -fxray-instrument flag set for the 493 // Clang/LLVM compiler. 494 // * The function is defined in the translation unit (the compiler honors the 495 // attribute in either the definition or the declaration, and must match). 496 // 497 // There are cases when, even when building with XRay instrumentation, users 498 // might want to control specifically which functions are instrumented for a 499 // particular build using special-case lists provided to the compiler. These 500 // special case lists are provided to Clang via the 501 // -fxray-always-instrument=... and -fxray-never-instrument=... flags. The 502 // attributes in source take precedence over these special-case lists. 503 // 504 // To disable the XRay attributes at build-time, users may define 505 // ABSL_NO_XRAY_ATTRIBUTES. Do NOT define ABSL_NO_XRAY_ATTRIBUTES on specific 506 // packages/targets, as this may lead to conflicting definitions of functions at 507 // link-time. 508 // 509 // XRay isn't currently supported on Android: 510 // https://github.com/android/ndk/issues/368 511 #if ABSL_HAVE_CPP_ATTRIBUTE(clang::xray_always_instrument) && \ 512 !defined(ABSL_NO_XRAY_ATTRIBUTES) && !defined(__ANDROID__) 513 #define ABSL_XRAY_ALWAYS_INSTRUMENT [[clang::xray_always_instrument]] 514 #define ABSL_XRAY_NEVER_INSTRUMENT [[clang::xray_never_instrument]] 515 #if ABSL_HAVE_CPP_ATTRIBUTE(clang::xray_log_args) 516 #define ABSL_XRAY_LOG_ARGS(N) \ 517 [[clang::xray_always_instrument, clang::xray_log_args(N)]] 518 #else 519 #define ABSL_XRAY_LOG_ARGS(N) [[clang::xray_always_instrument]] 520 #endif 521 #else 522 #define ABSL_XRAY_ALWAYS_INSTRUMENT 523 #define ABSL_XRAY_NEVER_INSTRUMENT 524 #define ABSL_XRAY_LOG_ARGS(N) 525 #endif 526 527 // ABSL_ATTRIBUTE_REINITIALIZES 528 // 529 // Indicates that a member function reinitializes the entire object to a known 530 // state, independent of the previous state of the object. 531 // 532 // The clang-tidy check bugprone-use-after-move allows member functions marked 533 // with this attribute to be called on objects that have been moved from; 534 // without the attribute, this would result in a use-after-move warning. 535 #if ABSL_HAVE_CPP_ATTRIBUTE(clang::reinitializes) 536 #define ABSL_ATTRIBUTE_REINITIALIZES [[clang::reinitializes]] 537 #else 538 #define ABSL_ATTRIBUTE_REINITIALIZES 539 #endif 540 541 // ----------------------------------------------------------------------------- 542 // Variable Attributes 543 // ----------------------------------------------------------------------------- 544 545 // ABSL_ATTRIBUTE_UNUSED 546 // 547 // Prevents the compiler from complaining about variables that appear unused. 548 // 549 // For code or headers that are assured to only build with C++17 and up, prefer 550 // just using the standard '[[maybe_unused]]' directly over this macro. 551 // 552 // Due to differences in positioning requirements between the old, compiler 553 // specific __attribute__ syntax and the now standard [[maybe_unused]], this 554 // macro does not attempt to take advantage of '[[maybe_unused]]'. 555 #if ABSL_HAVE_ATTRIBUTE(unused) || (defined(__GNUC__) && !defined(__clang__)) 556 #undef ABSL_ATTRIBUTE_UNUSED 557 #define ABSL_ATTRIBUTE_UNUSED __attribute__((__unused__)) 558 #else 559 #define ABSL_ATTRIBUTE_UNUSED 560 #endif 561 562 // ABSL_ATTRIBUTE_INITIAL_EXEC 563 // 564 // Tells the compiler to use "initial-exec" mode for a thread-local variable. 565 // See http://people.redhat.com/drepper/tls.pdf for the gory details. 566 #if ABSL_HAVE_ATTRIBUTE(tls_model) || (defined(__GNUC__) && !defined(__clang__)) 567 #define ABSL_ATTRIBUTE_INITIAL_EXEC __attribute__((tls_model("initial-exec"))) 568 #else 569 #define ABSL_ATTRIBUTE_INITIAL_EXEC 570 #endif 571 572 // ABSL_ATTRIBUTE_PACKED 573 // 574 // Instructs the compiler not to use natural alignment for a tagged data 575 // structure, but instead to reduce its alignment to 1. 576 // 577 // Therefore, DO NOT APPLY THIS ATTRIBUTE TO STRUCTS CONTAINING ATOMICS. Doing 578 // so can cause atomic variables to be mis-aligned and silently violate 579 // atomicity on x86. 580 // 581 // This attribute can either be applied to members of a structure or to a 582 // structure in its entirety. Applying this attribute (judiciously) to a 583 // structure in its entirety to optimize the memory footprint of very 584 // commonly-used structs is fine. Do not apply this attribute to a structure in 585 // its entirety if the purpose is to control the offsets of the members in the 586 // structure. Instead, apply this attribute only to structure members that need 587 // it. 588 // 589 // When applying ABSL_ATTRIBUTE_PACKED only to specific structure members the 590 // natural alignment of structure members not annotated is preserved. Aligned 591 // member accesses are faster than non-aligned member accesses even if the 592 // targeted microprocessor supports non-aligned accesses. 593 #if ABSL_HAVE_ATTRIBUTE(packed) || (defined(__GNUC__) && !defined(__clang__)) 594 #define ABSL_ATTRIBUTE_PACKED __attribute__((__packed__)) 595 #else 596 #define ABSL_ATTRIBUTE_PACKED 597 #endif 598 599 // ABSL_ATTRIBUTE_FUNC_ALIGN 600 // 601 // Tells the compiler to align the function start at least to certain 602 // alignment boundary 603 #if ABSL_HAVE_ATTRIBUTE(aligned) || (defined(__GNUC__) && !defined(__clang__)) 604 #define ABSL_ATTRIBUTE_FUNC_ALIGN(bytes) __attribute__((aligned(bytes))) 605 #else 606 #define ABSL_ATTRIBUTE_FUNC_ALIGN(bytes) 607 #endif 608 609 // ABSL_FALLTHROUGH_INTENDED 610 // 611 // Annotates implicit fall-through between switch labels, allowing a case to 612 // indicate intentional fallthrough and turn off warnings about any lack of a 613 // `break` statement. The ABSL_FALLTHROUGH_INTENDED macro should be followed by 614 // a semicolon and can be used in most places where `break` can, provided that 615 // no statements exist between it and the next switch label. 616 // 617 // Example: 618 // 619 // switch (x) { 620 // case 40: 621 // case 41: 622 // if (truth_is_out_there) { 623 // ++x; 624 // ABSL_FALLTHROUGH_INTENDED; // Use instead of/along with annotations 625 // // in comments 626 // } else { 627 // return x; 628 // } 629 // case 42: 630 // ... 631 // 632 // Notes: When supported, GCC and Clang can issue a warning on switch labels 633 // with unannotated fallthrough using the warning `-Wimplicit-fallthrough`. See 634 // clang documentation on language extensions for details: 635 // https://clang.llvm.org/docs/AttributeReference.html#fallthrough-clang-fallthrough 636 // 637 // When used with unsupported compilers, the ABSL_FALLTHROUGH_INTENDED macro has 638 // no effect on diagnostics. In any case this macro has no effect on runtime 639 // behavior and performance of code. 640 641 #ifdef ABSL_FALLTHROUGH_INTENDED 642 #error "ABSL_FALLTHROUGH_INTENDED should not be defined." 643 #elif ABSL_HAVE_CPP_ATTRIBUTE(fallthrough) 644 #define ABSL_FALLTHROUGH_INTENDED [[fallthrough]] 645 #elif ABSL_HAVE_CPP_ATTRIBUTE(clang::fallthrough) 646 #define ABSL_FALLTHROUGH_INTENDED [[clang::fallthrough]] 647 #elif ABSL_HAVE_CPP_ATTRIBUTE(gnu::fallthrough) 648 #define ABSL_FALLTHROUGH_INTENDED [[gnu::fallthrough]] 649 #else 650 #define ABSL_FALLTHROUGH_INTENDED \ 651 do { \ 652 } while (0) 653 #endif 654 655 // ABSL_DEPRECATED() 656 // 657 // Marks a deprecated class, struct, enum, function, method and variable 658 // declarations. The macro argument is used as a custom diagnostic message (e.g. 659 // suggestion of a better alternative). 660 // 661 // For code or headers that are assured to only build with C++14 and up, prefer 662 // just using the standard `[[deprecated("message")]]` directly over this macro. 663 // 664 // Examples: 665 // 666 // class ABSL_DEPRECATED("Use Bar instead") Foo {...}; 667 // 668 // ABSL_DEPRECATED("Use Baz() instead") void Bar() {...} 669 // 670 // template <typename T> 671 // ABSL_DEPRECATED("Use DoThat() instead") 672 // void DoThis(); 673 // 674 // enum FooEnum { 675 // kBar ABSL_DEPRECATED("Use kBaz instead"), 676 // }; 677 // 678 // Every usage of a deprecated entity will trigger a warning when compiled with 679 // GCC/Clang's `-Wdeprecated-declarations` option. Google's production toolchain 680 // turns this warning off by default, instead relying on clang-tidy to report 681 // new uses of deprecated code. 682 #if ABSL_HAVE_ATTRIBUTE(deprecated) 683 #define ABSL_DEPRECATED(message) __attribute__((deprecated(message))) 684 #else 685 #define ABSL_DEPRECATED(message) 686 #endif 687 688 // When deprecating Abseil code, it is sometimes necessary to turn off the 689 // warning within Abseil, until the deprecated code is actually removed. The 690 // deprecated code can be surrounded with these directives to achieve that 691 // result. 692 // 693 // class ABSL_DEPRECATED("Use Bar instead") Foo; 694 // 695 // ABSL_INTERNAL_DISABLE_DEPRECATED_DECLARATION_WARNING 696 // Baz ComputeBazFromFoo(Foo f); 697 // ABSL_INTERNAL_RESTORE_DEPRECATED_DECLARATION_WARNING 698 #if defined(__GNUC__) || defined(__clang__) 699 // Clang also supports these GCC pragmas. 700 #define ABSL_INTERNAL_DISABLE_DEPRECATED_DECLARATION_WARNING \ 701 _Pragma("GCC diagnostic push") \ 702 _Pragma("GCC diagnostic ignored \"-Wdeprecated-declarations\"") 703 #define ABSL_INTERNAL_RESTORE_DEPRECATED_DECLARATION_WARNING \ 704 _Pragma("GCC diagnostic pop") 705 #else 706 #define ABSL_INTERNAL_DISABLE_DEPRECATED_DECLARATION_WARNING 707 #define ABSL_INTERNAL_RESTORE_DEPRECATED_DECLARATION_WARNING 708 #endif // defined(__GNUC__) || defined(__clang__) 709 710 // ABSL_CONST_INIT 711 // 712 // A variable declaration annotated with the `ABSL_CONST_INIT` attribute will 713 // not compile (on supported platforms) unless the variable has a constant 714 // initializer. This is useful for variables with static and thread storage 715 // duration, because it guarantees that they will not suffer from the so-called 716 // "static init order fiasco". 717 // 718 // This attribute must be placed on the initializing declaration of the 719 // variable. Some compilers will give a -Wmissing-constinit warning when this 720 // attribute is placed on some other declaration but missing from the 721 // initializing declaration. 722 // 723 // In some cases (notably with thread_local variables), `ABSL_CONST_INIT` can 724 // also be used in a non-initializing declaration to tell the compiler that a 725 // variable is already initialized, reducing overhead that would otherwise be 726 // incurred by a hidden guard variable. Thus annotating all declarations with 727 // this attribute is recommended to potentially enhance optimization. 728 // 729 // Example: 730 // 731 // class MyClass { 732 // public: 733 // ABSL_CONST_INIT static MyType my_var; 734 // }; 735 // 736 // ABSL_CONST_INIT MyType MyClass::my_var = MakeMyType(...); 737 // 738 // For code or headers that are assured to only build with C++20 and up, prefer 739 // just using the standard `constinit` keyword directly over this macro. 740 // 741 // Note that this attribute is redundant if the variable is declared constexpr. 742 #if defined(__cpp_constinit) && __cpp_constinit >= 201907L 743 #define ABSL_CONST_INIT constinit 744 #elif ABSL_HAVE_CPP_ATTRIBUTE(clang::require_constant_initialization) 745 #define ABSL_CONST_INIT [[clang::require_constant_initialization]] 746 #else 747 #define ABSL_CONST_INIT 748 #endif 749 750 // ABSL_ATTRIBUTE_PURE_FUNCTION 751 // 752 // ABSL_ATTRIBUTE_PURE_FUNCTION is used to annotate declarations of "pure" 753 // functions. A function is pure if its return value is only a function of its 754 // arguments. The pure attribute prohibits a function from modifying the state 755 // of the program that is observable by means other than inspecting the 756 // function's return value. Declaring such functions with the pure attribute 757 // allows the compiler to avoid emitting some calls in repeated invocations of 758 // the function with the same argument values. 759 // 760 // Example: 761 // 762 // ABSL_ATTRIBUTE_PURE_FUNCTION std::string FormatTime(Time t); 763 #if ABSL_HAVE_CPP_ATTRIBUTE(gnu::pure) 764 #define ABSL_ATTRIBUTE_PURE_FUNCTION [[gnu::pure]] 765 #elif ABSL_HAVE_ATTRIBUTE(pure) 766 #define ABSL_ATTRIBUTE_PURE_FUNCTION __attribute__((pure)) 767 #else 768 // If the attribute isn't defined, we'll fallback to ABSL_MUST_USE_RESULT since 769 // pure functions are useless if its return is ignored. 770 #define ABSL_ATTRIBUTE_PURE_FUNCTION ABSL_MUST_USE_RESULT 771 #endif 772 773 // ABSL_ATTRIBUTE_CONST_FUNCTION 774 // 775 // ABSL_ATTRIBUTE_CONST_FUNCTION is used to annotate declarations of "const" 776 // functions. A const function is similar to a pure function, with one 777 // exception: Pure functions may return value that depend on a non-volatile 778 // object that isn't provided as a function argument, while the const function 779 // is guaranteed to return the same result given the same arguments. 780 // 781 // Example: 782 // 783 // ABSL_ATTRIBUTE_CONST_FUNCTION int64_t ToInt64Milliseconds(Duration d); 784 #if defined(_MSC_VER) && !defined(__clang__) 785 // Put the MSVC case first since MSVC seems to parse const as a C++ keyword. 786 #define ABSL_ATTRIBUTE_CONST_FUNCTION ABSL_ATTRIBUTE_PURE_FUNCTION 787 #elif ABSL_HAVE_CPP_ATTRIBUTE(gnu::const) 788 #define ABSL_ATTRIBUTE_CONST_FUNCTION [[gnu::const]] 789 #elif ABSL_HAVE_ATTRIBUTE(const) 790 #define ABSL_ATTRIBUTE_CONST_FUNCTION __attribute__((const)) 791 #else 792 // Since const functions are more restrictive pure function, we'll fallback to a 793 // pure function if the const attribute is not handled. 794 #define ABSL_ATTRIBUTE_CONST_FUNCTION ABSL_ATTRIBUTE_PURE_FUNCTION 795 #endif 796 797 // ABSL_ATTRIBUTE_LIFETIME_BOUND indicates that a resource owned by a function 798 // parameter or implicit object parameter is retained by the return value of the 799 // annotated function (or, for a parameter of a constructor, in the value of the 800 // constructed object). This attribute causes warnings to be produced if a 801 // temporary object does not live long enough. 802 // 803 // When applied to a reference parameter, the referenced object is assumed to be 804 // retained by the return value of the function. When applied to a non-reference 805 // parameter (for example, a pointer or a class type), all temporaries 806 // referenced by the parameter are assumed to be retained by the return value of 807 // the function. 808 // 809 // See also the upstream documentation: 810 // https://clang.llvm.org/docs/AttributeReference.html#lifetimebound 811 #if ABSL_HAVE_CPP_ATTRIBUTE(clang::lifetimebound) 812 #define ABSL_ATTRIBUTE_LIFETIME_BOUND [[clang::lifetimebound]] 813 #elif ABSL_HAVE_ATTRIBUTE(lifetimebound) 814 #define ABSL_ATTRIBUTE_LIFETIME_BOUND __attribute__((lifetimebound)) 815 #else 816 #define ABSL_ATTRIBUTE_LIFETIME_BOUND 817 #endif 818 819 // ABSL_ATTRIBUTE_TRIVIAL_ABI 820 // Indicates that a type is "trivially relocatable" -- meaning it can be 821 // relocated without invoking the constructor/destructor, using a form of move 822 // elision. 823 // 824 // From a memory safety point of view, putting aside destructor ordering, it's 825 // safe to apply ABSL_ATTRIBUTE_TRIVIAL_ABI if an object's location 826 // can change over the course of its lifetime: if a constructor can be run one 827 // place, and then the object magically teleports to another place where some 828 // methods are run, and then the object teleports to yet another place where it 829 // is destroyed. This is notably not true for self-referential types, where the 830 // move-constructor must keep the self-reference up to date. If the type changed 831 // location without invoking the move constructor, it would have a dangling 832 // self-reference. 833 // 834 // The use of this teleporting machinery means that the number of paired 835 // move/destroy operations can change, and so it is a bad idea to apply this to 836 // a type meant to count the number of moves. 837 // 838 // Warning: applying this can, rarely, break callers. Objects passed by value 839 // will be destroyed at the end of the call, instead of the end of the 840 // full-expression containing the call. In addition, it changes the ABI 841 // of functions accepting this type by value (e.g. to pass in registers). 842 // 843 // See also the upstream documentation: 844 // https://clang.llvm.org/docs/AttributeReference.html#trivial-abi 845 // 846 // b/321691395 - This is currently disabled in open-source builds since 847 // compiler support differs. If system libraries compiled with GCC are mixed 848 // with libraries compiled with Clang, types will have different ideas about 849 // their ABI, leading to hard to debug crashes. 850 #define ABSL_ATTRIBUTE_TRIVIAL_ABI 851 852 // ABSL_ATTRIBUTE_NO_UNIQUE_ADDRESS 853 // 854 // Indicates a data member can be optimized to occupy no space (if it is empty) 855 // and/or its tail padding can be used for other members. 856 // 857 // For code that is assured to only build with C++20 or later, prefer using 858 // the standard attribute `[[no_unique_address]]` directly instead of this 859 // macro. 860 // 861 // https://devblogs.microsoft.com/cppblog/msvc-cpp20-and-the-std-cpp20-switch/#c20-no_unique_address 862 // Current versions of MSVC have disabled `[[no_unique_address]]` since it 863 // breaks ABI compatibility, but offers `[[msvc::no_unique_address]]` for 864 // situations when it can be assured that it is desired. Since Abseil does not 865 // claim ABI compatibility in mixed builds, we can offer it unconditionally. 866 #if defined(_MSC_VER) && _MSC_VER >= 1929 867 #define ABSL_ATTRIBUTE_NO_UNIQUE_ADDRESS [[msvc::no_unique_address]] 868 #elif ABSL_HAVE_CPP_ATTRIBUTE(no_unique_address) 869 #define ABSL_ATTRIBUTE_NO_UNIQUE_ADDRESS [[no_unique_address]] 870 #else 871 #define ABSL_ATTRIBUTE_NO_UNIQUE_ADDRESS 872 #endif 873 874 // ABSL_ATTRIBUTE_UNINITIALIZED 875 // 876 // GCC and Clang support a flag `-ftrivial-auto-var-init=<option>` (<option> 877 // can be "zero" or "pattern") that can be used to initialize automatic stack 878 // variables. Variables with this attribute will be left uninitialized, 879 // overriding the compiler flag. 880 // 881 // See https://clang.llvm.org/docs/AttributeReference.html#uninitialized 882 // and https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-uninitialized-variable-attribute 883 #if ABSL_HAVE_CPP_ATTRIBUTE(clang::uninitialized) 884 #define ABSL_ATTRIBUTE_UNINITIALIZED [[clang::uninitialized]] 885 #elif ABSL_HAVE_CPP_ATTRIBUTE(gnu::uninitialized) 886 #define ABSL_ATTRIBUTE_UNINITIALIZED [[gnu::uninitialized]] 887 #elif ABSL_HAVE_ATTRIBUTE(uninitialized) 888 #define ABSL_ATTRIBUTE_UNINITIALIZED __attribute__((uninitialized)) 889 #else 890 #define ABSL_ATTRIBUTE_UNINITIALIZED 891 #endif 892 893 // ABSL_ATTRIBUTE_WARN_UNUSED 894 // 895 // Compilers routinely warn about trivial variables that are unused. For 896 // non-trivial types, this warning is suppressed since the 897 // constructor/destructor may be intentional and load-bearing, for example, with 898 // a RAII scoped lock. 899 // 900 // For example: 901 // 902 // class ABSL_ATTRIBUTE_WARN_UNUSED MyType { 903 // public: 904 // MyType(); 905 // ~MyType(); 906 // }; 907 // 908 // void foo() { 909 // // Warns with ABSL_ATTRIBUTE_WARN_UNUSED attribute present. 910 // MyType unused; 911 // } 912 // 913 // See https://clang.llvm.org/docs/AttributeReference.html#warn-unused and 914 // https://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Attributes.html#index-warn_005funused-type-attribute 915 #if ABSL_HAVE_CPP_ATTRIBUTE(gnu::warn_unused) 916 #define ABSL_ATTRIBUTE_WARN_UNUSED [[gnu::warn_unused]] 917 #else 918 #define ABSL_ATTRIBUTE_WARN_UNUSED 919 #endif 920 921 #endif // ABSL_BASE_ATTRIBUTES_H_ 922