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Willy Tarreaucc05fba2009-10-27 21:40:18 +01001/*
2 * include/common/compiler.h
3 * This files contains some compiler-specific settings.
4 *
5 * Copyright (C) 2000-2009 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
Willy Tarreauf3bfede2011-07-25 11:38:17 +020019 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
Willy Tarreaucc05fba2009-10-27 21:40:18 +010020 */
21
22#ifndef _COMMON_COMPILER_H
23#define _COMMON_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 __GNUC__ < 3
31#define VAR_ARRAY 0
32#else
33#define VAR_ARRAY
34#endif
35#endif
36
37
38/* Support passing function parameters in registers. For this, the
39 * CONFIG_REGPARM macro has to be set to the maximal number of registers
40 * allowed. Some functions have intentionally received a regparm lower than
41 * their parameter count, it is in order to avoid register clobbering where
42 * they are called.
43 */
44#ifndef REGPRM1
45#if CONFIG_REGPARM >= 1 && __GNUC__ >= 3
46#define REGPRM1 __attribute__((regparm(1)))
47#else
48#define REGPRM1
49#endif
50#endif
51
52#ifndef REGPRM2
53#if CONFIG_REGPARM >= 2 && __GNUC__ >= 3
54#define REGPRM2 __attribute__((regparm(2)))
55#else
56#define REGPRM2 REGPRM1
57#endif
58#endif
59
60#ifndef REGPRM3
61#if CONFIG_REGPARM >= 3 && __GNUC__ >= 3
62#define REGPRM3 __attribute__((regparm(3)))
63#else
64#define REGPRM3 REGPRM2
65#endif
66#endif
67
68
69/* By default, gcc does not inline large chunks of code, but we want it to
70 * respect our choices.
71 */
72#if !defined(forceinline)
73#if __GNUC__ < 3
74#define forceinline inline
75#else
76#define forceinline inline __attribute__((always_inline))
77#endif
78#endif
79
Willy Tarreaudbd25fc2017-11-20 21:22:17 +010080/* silence the "unused" warnings without having to place painful #ifdefs.
81 * For use with variables or functions.
82 */
83#define __maybe_unused __attribute__((unused))
Willy Tarreaucc05fba2009-10-27 21:40:18 +010084
Willy Tarreau8d26f022018-10-15 11:53:34 +020085/* This allows gcc to know that some locations are never reached, for example
86 * after a longjmp() in the Lua code, hence that some errors caught by such
87 * methods cannot propagate further. This is important with gcc versions 6 and
88 * above which can more aggressively detect null dereferences. The builtin
89 * below was introduced in gcc 4.5, and before it we didn't care.
90 */
91#if __GNUC__ >= 5 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 5)
92#define __unreachable() __builtin_unreachable()
93#else
94#define __unreachable()
95#endif
96
Willy Tarreaucc05fba2009-10-27 21:40:18 +010097/*
98 * Gcc >= 3 provides the ability for the programme to give hints to the
99 * compiler about what branch of an if is most likely to be taken. This
100 * helps the compiler produce the most compact critical paths, which is
101 * generally better for the cache and to reduce the number of jumps.
102 */
103#if !defined(likely)
104#if __GNUC__ < 3
105#define __builtin_expect(x,y) (x)
106#define likely(x) (x)
107#define unlikely(x) (x)
Willy Tarreauc9398352017-10-08 22:26:03 +0200108#elif __GNUC__ < 4 || __GNUC__ >= 5
109/* gcc 3.x and 5.x do the best job at this */
Willy Tarreaucc05fba2009-10-27 21:40:18 +0100110#define likely(x) (__builtin_expect((x) != 0, 1))
111#define unlikely(x) (__builtin_expect((x) != 0, 0))
112#else
113/* GCC 4.x is stupid, it performs the comparison then compares it to 1,
114 * so we cheat in a dirty way to prevent it from doing this. This will
115 * only work with ints and booleans though.
116 */
117#define likely(x) (x)
118#define unlikely(x) (__builtin_expect((unsigned long)(x), 0))
119#endif
120#endif
121
Olivier Houchard928fbfa2018-01-24 18:17:06 +0100122#ifndef __GNUC_PREREQ__
123#if defined(__GNUC__) && !defined(__INTEL_COMPILER)
124#define __GNUC_PREREQ__(ma, mi) \
125 (__GNUC__ > (ma) || __GNUC__ == (ma) && __GNUC_MINOR__ >= (mi))
126#else
127#define __GNUC_PREREQ__(ma, mi) 0
128#endif
129#endif
130
131#ifndef offsetof
132#if __GNUC_PREREQ__(4, 1)
133#define offsetof(type, field) __builtin_offsetof(type, field)
134#else
135#define offsetof(type, field) \
Willy Tarreauc03ea402018-07-30 11:47:35 +0200136 ((size_t)(uintptr_t)((const volatile void *)&((type *)0)->field))
Olivier Houchard928fbfa2018-01-24 18:17:06 +0100137#endif
138#endif
139
Willy Tarreaucc05fba2009-10-27 21:40:18 +0100140
141#endif /* _COMMON_COMPILER_H */