1 /* 2 * include/haproxy/compiler.h 3 * This files contains some compiler-specific settings. 4 * 5 * Copyright (C) 2000-2020 Willy Tarreau - w@1wt.eu 6 * 7 * This library is free software; you can redistribute it and/or 8 * modify it under the terms of the GNU Lesser General Public 9 * License as published by the Free Software Foundation, version 2.1 10 * exclusively. 11 * 12 * This library is distributed in the hope that it will be useful, 13 * but WITHOUT ANY WARRANTY; without even the implied warranty of 14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 15 * Lesser General Public License for more details. 16 * 17 * You should have received a copy of the GNU Lesser General Public 18 * License along with this library; if not, write to the Free Software 19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA 20 */ 21 22 #ifndef _HAPROXY_COMPILER_H 23 #define _HAPROXY_COMPILER_H 24 25 26 /* 27 * Gcc before 3.0 needs [0] to declare a variable-size array 28 */ 29 #ifndef VAR_ARRAY 30 #if defined(__GNUC__) && (__GNUC__ < 3) 31 #define VAR_ARRAY 0 32 #else 33 #define VAR_ARRAY 34 #endif 35 #endif 36 37 #if !defined(__GNUC__) 38 /* Some versions of glibc irresponsibly redefine __attribute__() to empty for 39 * non-gcc compilers, and as such, silently break all constructors with other 40 * other compilers. Let's make sure such incompatibilities are detected if any, 41 * or that the attribute is properly enforced. 42 */ 43 #undef __attribute__ 44 #define __attribute__(x) __attribute__(x) 45 #endif 46 47 /* By default, gcc does not inline large chunks of code, but we want it to 48 * respect our choices. 49 */ 50 #if !defined(forceinline) 51 #if !defined(__GNUC__) || (__GNUC__ < 3) 52 #define forceinline inline 53 #else 54 #define forceinline inline __attribute__((always_inline)) 55 #endif 56 #endif 57 58 /* silence the "unused" warnings without having to place painful #ifdefs. 59 * For use with variables or functions. 60 */ 61 #define __maybe_unused __attribute__((unused)) 62 63 /* This allows gcc to know that some locations are never reached, for example 64 * after a longjmp() in the Lua code, hence that some errors caught by such 65 * methods cannot propagate further. This is important with gcc versions 6 and 66 * above which can more aggressively detect null dereferences. The builtin 67 * below was introduced in gcc 4.5, and before it we didn't care. 68 */ 69 #if __GNUC__ >= 5 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 5) 70 #define my_unreachable() __builtin_unreachable() 71 #else 72 #define my_unreachable() 73 #endif 74 75 /* This macro may be used to block constant propagation that lets the compiler 76 * detect a possible NULL dereference on a variable resulting from an explicit 77 * assignment in an impossible check. Sometimes a function is called which does 78 * safety checks and returns NULL if safe conditions are not met. The place 79 * where it's called cannot hit this condition and dereferencing the pointer 80 * without first checking it will make the compiler emit a warning about a 81 * "potential null pointer dereference" which is hard to work around. This 82 * macro "washes" the pointer and prevents the compiler from emitting tests 83 * branching to undefined instructions. It may only be used when the developer 84 * is absolutely certain that the conditions are guaranteed and that the 85 * pointer passed in argument cannot be NULL by design. 86 */ 87 #define ALREADY_CHECKED(p) do { asm("" : "=rm"(p) : "0"(p)); } while (0) 88 89 /* same as above but to be used to pass the input value to the output but 90 * without letting the compiler know about its initial properties. 91 */ 92 #define DISGUISE(v) ({ typeof(v) __v = (v); ALREADY_CHECKED(__v); __v; }) 93 94 /* Implements a static event counter where it's used. This is typically made to 95 * report some warnings only once, either during boot or at runtime. It only 96 * returns true on the very first call, and zero later. It's thread-safe and 97 * uses a single byte of memory per call place. It relies on the atomic xchg 98 * defined in atomic.h which is also part of the common API. 99 */ 100 #define ONLY_ONCE() ({ static char __cnt; !_HA_ATOMIC_XCHG(&__cnt, 1); }) 101 102 /* 103 * Gcc >= 3 provides the ability for the program to give hints to the 104 * compiler about what branch of an if is most likely to be taken. This 105 * helps the compiler produce the most compact critical paths, which is 106 * generally better for the cache and to reduce the number of jumps. 107 */ 108 #if !defined(likely) 109 #if !defined(__GNUC__) || (__GNUC__ < 3) 110 #define __builtin_expect(x,y) (x) 111 #define likely(x) (x) 112 #define unlikely(x) (x) 113 #else 114 #define likely(x) (__builtin_expect((x) != 0, 1)) 115 #define unlikely(x) (__builtin_expect((x) != 0, 0)) 116 #endif 117 #endif 118 119 #ifndef __GNUC_PREREQ__ 120 #if defined(__GNUC__) && !defined(__INTEL_COMPILER) 121 #define __GNUC_PREREQ__(ma, mi) \ 122 (__GNUC__ > (ma) || __GNUC__ == (ma) && __GNUC_MINOR__ >= (mi)) 123 #else 124 #define __GNUC_PREREQ__(ma, mi) 0 125 #endif 126 #endif 127 128 #ifndef offsetof 129 #if __GNUC_PREREQ__(4, 1) 130 #define offsetof(type, field) __builtin_offsetof(type, field) 131 #else 132 #define offsetof(type, field) \ 133 ((size_t)(uintptr_t)((const volatile void *)&((type *)0)->field)) 134 #endif 135 #endif 136 137 /* Some architectures have a double-word CAS, sometimes even dual-8 bytes. 138 * Some architectures support unaligned accesses, others are fine with them 139 * but only for non-atomic operations. Also mention those supporting unaligned 140 * accesses and being little endian, and those where unaligned accesses are 141 * known to be fast (almost as fast as aligned ones). 142 */ 143 #if defined(__x86_64__) 144 #define HA_UNALIGNED 145 #define HA_UNALIGNED_LE 146 #define HA_UNALIGNED_LE64 147 #define HA_UNALIGNED_FAST 148 #define HA_UNALIGNED_ATOMIC 149 #define HA_HAVE_CAS_DW 150 #define HA_CAS_IS_8B 151 #elif defined(__i386__) || defined(__i486__) || defined(__i586__) || defined(__i686__) 152 #define HA_UNALIGNED 153 #define HA_UNALIGNED_LE 154 #define HA_UNALIGNED_ATOMIC 155 #elif defined (__aarch64__) || defined(__ARM_ARCH_8A) 156 #define HA_UNALIGNED 157 #define HA_UNALIGNED_LE 158 #define HA_UNALIGNED_LE64 159 #define HA_UNALIGNED_FAST 160 #define HA_HAVE_CAS_DW 161 #define HA_CAS_IS_8B 162 #elif defined(__arm__) && (defined(__ARM_ARCH_7__) || defined(__ARM_ARCH_7A__)) 163 #define HA_UNALIGNED 164 #define HA_UNALIGNED_LE 165 #define HA_UNALIGNED_FAST 166 #define HA_HAVE_CAS_DW 167 #endif 168 169 170 /* sets alignment for current field or variable */ 171 #ifndef ALIGNED 172 #define ALIGNED(x) __attribute__((aligned(x))) 173 #endif 174 175 /* sets alignment only on architectures preventing unaligned atomic accesses */ 176 #ifndef MAYBE_ALIGNED 177 #ifndef HA_UNALIGNED 178 #define MAYBE_ALIGNED(x) ALIGNED(x) 179 #else 180 #define MAYBE_ALIGNED(x) 181 #endif 182 #endif 183 184 /* sets alignment only on architectures preventing unaligned atomic accesses */ 185 #ifndef ATOMIC_ALIGNED 186 #ifndef HA_UNALIGNED_ATOMIC 187 #define ATOMIC_ALIGNED(x) ALIGNED(x) 188 #else 189 #define ATOMIC_ALIGNED(x) 190 #endif 191 #endif 192 193 /* sets alignment for current field or variable only when threads are enabled. 194 * Typically used to respect cache line alignment to avoid false sharing. 195 */ 196 #ifndef THREAD_ALIGNED 197 #ifdef USE_THREAD 198 #define THREAD_ALIGNED(x) __attribute__((aligned(x))) 199 #else 200 #define THREAD_ALIGNED(x) 201 #endif 202 #endif 203 204 /* add a mandatory alignment for next fields in a structure */ 205 #ifndef ALWAYS_ALIGN 206 #define ALWAYS_ALIGN(x) union { } ALIGNED(x) 207 #endif 208 209 /* add an optional alignment for next fields in a structure, only for archs 210 * which do not support unaligned accesses. 211 */ 212 #ifndef MAYBE_ALIGN 213 #ifndef HA_UNALIGNED 214 #define MAYBE_ALIGN(x) union { } ALIGNED(x) 215 #else 216 #define MAYBE_ALIGN(x) 217 #endif 218 #endif 219 220 /* add an optional alignment for next fields in a structure, only for archs 221 * which do not support unaligned accesses for atomic operations. 222 */ 223 #ifndef ATOMIC_ALIGN 224 #ifndef HA_UNALIGNED_ATOMIC 225 #define ATOMIC_ALIGN(x) union { } ALIGNED(x) 226 #else 227 #define ATOMIC_ALIGN(x) 228 #endif 229 #endif 230 231 /* add an optional alignment for next fields in a structure, only when threads 232 * are enabled. Typically used to respect cache line alignment to avoid false 233 * sharing. 234 */ 235 #ifndef THREAD_ALIGN 236 #ifdef USE_THREAD 237 #define THREAD_ALIGN(x) union { } ALIGNED(x) 238 #else 239 #define THREAD_ALIGN(x) 240 #endif 241 #endif 242 243 /* The THREAD_LOCAL type attribute defines thread-local storage and is defined 244 * to __thread when threads are enabled or empty when disabled. 245 */ 246 #ifdef USE_THREAD 247 #define THREAD_LOCAL __thread 248 #else 249 #define THREAD_LOCAL 250 #endif 251 252 /* The __decl_thread() statement is shows the argument when threads are enabled 253 * or hides it when disabled. The purpose is to condition the presence of some 254 * variables or struct members to the fact that threads are enabled, without 255 * having to enclose them inside a #ifdef USE_THREAD/#endif clause. 256 */ 257 #ifdef USE_THREAD 258 #define __decl_thread(decl) decl 259 #else 260 #define __decl_thread(decl) 261 #endif 262 263 /* clang has a __has_feature() macro which reports true/false on a number of 264 * internally supported features. Let's make sure this macro is always defined 265 * and returns zero when not supported. 266 */ 267 #ifndef __has_feature 268 #define __has_feature(x) 0 269 #endif 270 271 #endif /* _HAPROXY_COMPILER_H */ 272