path: root/include/openvswitch/compiler.h

/*
 * Copyright (c) 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2016, 2017 Nicira, Inc.
 *
 * 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:
 *
 *     http://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.
 */

#ifndef OPENVSWITCH_COMPILER_H
#define OPENVSWITCH_COMPILER_H 1

#include <stddef.h>
#include <stdbool.h>

#ifndef __has_feature
  #define __has_feature(x) 0
#endif
#ifndef __has_extension
  #define __has_extension(x) 0
#endif

/* To make OVS_NO_RETURN portable across gcc/clang and MSVC, it should be
 * added at the beginning of the function declaration. */
#if __GNUC__ && !__CHECKER__
#define OVS_NO_RETURN __attribute__((__noreturn__))
#elif _MSC_VER
#define OVS_NO_RETURN __declspec(noreturn)
#else
#define OVS_NO_RETURN
#endif

#if __GNUC__ && !__CHECKER__
#define OVS_UNUSED __attribute__((__unused__))
#define OVS_PRINTF_FORMAT(FMT, ARG1) __attribute__((__format__(printf, FMT, ARG1)))
#define OVS_SCANF_FORMAT(FMT, ARG1) __attribute__((__format__(scanf, FMT, ARG1)))
#define OVS_WARN_UNUSED_RESULT __attribute__((__warn_unused_result__))
#define OVS_LIKELY(CONDITION) __builtin_expect(!!(CONDITION), 1)
#define OVS_UNLIKELY(CONDITION) __builtin_expect(!!(CONDITION), 0)
#else
#define OVS_UNUSED
#define OVS_PRINTF_FORMAT(FMT, ARG1)
#define OVS_SCANF_FORMAT(FMT, ARG1)
#define OVS_WARN_UNUSED_RESULT
#define OVS_LIKELY(CONDITION) (!!(CONDITION))
#define OVS_UNLIKELY(CONDITION) (!!(CONDITION))
#endif

#if __has_feature(c_thread_safety_attributes)
/* "clang" annotations for thread safety check.
 *
 * OVS_LOCKABLE indicates that the struct contains mutex element
 * which can be locked by functions like ovs_mutex_lock().
 *
 * Below, the word MUTEX stands for the name of an object with an OVS_LOCKABLE
 * struct type.  It can also be a comma-separated list of multiple structs,
 * e.g. to require a function to hold multiple locks while invoked.
 *
 *
 * On a variable:
 *
 *    - OVS_GUARDED indicates that the variable may only be accessed some mutex
 *      is held.
 *
 *    - OVS_GUARDED_BY(MUTEX) indicates that the variable may only be accessed
 *      while the specific MUTEX is held.
 *
 *
 * On a variable A of mutex type:
 *
 *    - OVS_ACQ_BEFORE(B), where B is a mutex or a comma-separated list of
 *      mutexes, declare that if both A and B are acquired at the same time,
 *      then A must be acquired before B.  That is, B nests inside A.
 *
 *    - OVS_ACQ_AFTER(B) is the opposite of OVS_ACQ_BEFORE(B), that is, it
 *      declares that A nests inside B.
 *
 *
 * On a function, the following attributes apply to mutexes:
 *
 *    - OVS_ACQUIRES(MUTEX) indicate that the function must be called without
 *      holding MUTEX and that it returns holding MUTEX.
 *
 *    - OVS_RELEASES(MUTEX) indicates that the function may only be called with
 *      MUTEX held and that it returns with MUTEX released.  It can be used for
 *      all types of MUTEX.
 *
 *    - OVS_TRY_LOCK(RETVAL, MUTEX) indicate that the function will try to
 *      acquire MUTEX.  RETVAL is an integer or boolean value specifying the
 *      return value of a successful lock acquisition.
 *
 *    - OVS_REQUIRES(MUTEX) indicate that the function may only be called with
 *      MUTEX held and that the function does not release MUTEX.
 *
 *    - OVS_EXCLUDED(MUTEX) indicates that the function may only be called when
 *      MUTEX is not held.
 *
 *
 * The following variants, with the same syntax, apply to reader-writer locks:
 *
 *    mutex                rwlock, for reading  rwlock, for writing
 *    -------------------  -------------------  -------------------
 *    OVS_ACQUIRES         OVS_ACQ_RDLOCK       OVS_ACQ_WRLOCK
 *    OVS_RELEASES         OVS_RELEASES         OVS_RELEASES
 *    OVS_TRY_LOCK         OVS_TRY_RDLOCK       OVS_TRY_WRLOCK
 *    OVS_REQUIRES         OVS_REQ_RDLOCK       OVS_REQ_WRLOCK
 *    OVS_EXCLUDED         OVS_EXCLUDED         OVS_EXCLUDED
 */
#define OVS_LOCKABLE __attribute__((lockable))
#define OVS_REQ_RDLOCK(...) __attribute__((shared_locks_required(__VA_ARGS__)))
#define OVS_ACQ_RDLOCK(...) __attribute__((shared_lock_function(__VA_ARGS__)))
#define OVS_REQ_WRLOCK(...) \
    __attribute__((exclusive_locks_required(__VA_ARGS__)))
#define OVS_ACQ_WRLOCK(...) \
    __attribute__((exclusive_lock_function(__VA_ARGS__)))
#define OVS_REQUIRES(...) \
    __attribute__((exclusive_locks_required(__VA_ARGS__)))
#define OVS_ACQUIRES(...) \
    __attribute__((exclusive_lock_function(__VA_ARGS__)))
#define OVS_TRY_WRLOCK(RETVAL, ...)                              \
    __attribute__((exclusive_trylock_function(RETVAL, __VA_ARGS__)))
#define OVS_TRY_RDLOCK(RETVAL, ...)                          \
    __attribute__((shared_trylock_function(RETVAL, __VA_ARGS__)))
#define OVS_TRY_LOCK(RETVAL, ...)                                \
    __attribute__((exclusive_trylock_function(RETVAL, __VA_ARGS__)))
#define OVS_GUARDED __attribute__((guarded_var))
#define OVS_GUARDED_BY(...) __attribute__((guarded_by(__VA_ARGS__)))
#define OVS_RELEASES(...) __attribute__((unlock_function(__VA_ARGS__)))
#define OVS_EXCLUDED(...) __attribute__((locks_excluded(__VA_ARGS__)))
#define OVS_ACQ_BEFORE(...) __attribute__((acquired_before(__VA_ARGS__)))
#define OVS_ACQ_AFTER(...) __attribute__((acquired_after(__VA_ARGS__)))
#define OVS_NO_THREAD_SAFETY_ANALYSIS \
    __attribute__((no_thread_safety_analysis))
#else  /* not Clang */
#define OVS_LOCKABLE
#define OVS_REQ_RDLOCK(...)
#define OVS_ACQ_RDLOCK(...)
#define OVS_REQ_WRLOCK(...)
#define OVS_ACQ_WRLOCK(...)
#define OVS_REQUIRES(...)
#define OVS_ACQUIRES(...)
#define OVS_TRY_WRLOCK(...)
#define OVS_TRY_RDLOCK(...)
#define OVS_TRY_LOCK(...)
#define OVS_GUARDED
#define OVS_GUARDED_BY(...)
#define OVS_EXCLUDED(...)
#define OVS_RELEASES(...)
#define OVS_ACQ_BEFORE(...)
#define OVS_ACQ_AFTER(...)
#define OVS_NO_THREAD_SAFETY_ANALYSIS
#endif

/* ISO C says that a C implementation may choose any integer type for an enum
 * that is sufficient to hold all of its values.  Common ABIs (such as the
 * System V ABI used on i386 GNU/Linux) always use a full-sized "int", even
 * when a smaller type would suffice.
 *
 * In GNU C, "enum __attribute__((packed)) name { ... }" defines 'name' as an
 * enum compatible with a type that is no bigger than necessary.  This is the
 * intended use of OVS_PACKED_ENUM.
 *
 * OVS_PACKED_ENUM is intended for use only as a space optimization, since it
 * only works with GCC.  That means that it must not be used in wire protocols
 * or otherwise exposed outside of a single process. */
#if __GNUC__ && !__CHECKER__
#define OVS_PACKED_ENUM __attribute__((__packed__))
#define HAVE_PACKED_ENUM
#else
#define OVS_PACKED_ENUM
#endif

#ifndef _MSC_VER
#define OVS_PACKED(DECL) DECL __attribute__((__packed__))
#else
#define OVS_PACKED(DECL) __pragma(pack(push, 1)) DECL __pragma(pack(pop))
#endif

/* OVS_ALIGNED_STRUCT may be used to define a structure whose instances should
 * aligned on an N-byte boundary.  This:
 *     OVS_ALIGNED_STRUCT(64, mystruct) { ... };
 * is equivalent to the following except that it specifies 64-byte alignment:
 *     struct mystruct { ... };
 *
 * OVS_ALIGNED_VAR defines a variable aligned on an N-byte boundary.  For
 * example,
 *     OVS_ALIGNED_VAR(64) int x;
 * defines a "int" variable that is aligned on a 64-byte boundary.
 */
#ifndef _MSC_VER
#define OVS_ALIGNED_STRUCT(N, TAG) struct __attribute__((aligned(N))) TAG
#define OVS_ALIGNED_VAR(N) __attribute__((aligned(N)))
#else
#define OVS_ALIGNED_STRUCT(N, TAG) __declspec(align(N)) struct TAG
#define OVS_ALIGNED_VAR(N) __declspec(align(N))
#endif

/* Supplies code to be run at startup time before invoking main().
 * Use as:
 *
 *     OVS_CONSTRUCTOR(my_constructor) {
 *         ...some code...
 *     }
 */
#ifdef _MSC_VER
#define CCALL __cdecl
#pragma section(".CRT$XCU",read)
#define OVS_CONSTRUCTOR(f) \
    static void __cdecl f(void); \
    __declspec(allocate(".CRT$XCU")) static void (__cdecl*f##_)(void) = f; \
    static void __cdecl f(void)
#else
#define OVS_CONSTRUCTOR(f) \
    static void f(void) __attribute__((constructor)); \
    static void f(void)
#endif

/* OVS_PREFETCH() can be used to instruct the CPU to fetch the cache
 * line containing the given address to a CPU cache.
 * OVS_PREFETCH_WRITE() should be used when the memory is going to be
 * written to.  Depending on the target CPU, this can generate the same
 * instruction as OVS_PREFETCH(), or bring the data into the cache in an
 * exclusive state. */
#if __GNUC__
#define OVS_PREFETCH(addr) __builtin_prefetch((addr))
#define OVS_PREFETCH_WRITE(addr) __builtin_prefetch((addr), 1)
#else
#define OVS_PREFETCH(addr)
#define OVS_PREFETCH_WRITE(addr)
#endif

/* Since Visual Studio 2015 there has been an effort to make offsetof a
 * builtin_offsetof, unfortunately both implementation (the regular define and
 * the built in one) are buggy and cause issues when using them via
 * the C compiler.
 * e.g.: https://bit.ly/2UvWwti
 */
#if _MSC_VER >= 1900
#undef offsetof
#define offsetof(type, member) \
    ((size_t)((char *)&(((type *)0)->member) - (char *)0))
#endif

/* Build assertions.
 *
 * Use BUILD_ASSERT_DECL as a declaration or a statement, or BUILD_ASSERT as
 * part of an expression. */
#ifdef __CHECKER__
#define BUILD_ASSERT(EXPR) ((void) 0)
#define BUILD_ASSERT_DECL(EXPR) extern int (*build_assert(void))[1]
#elif defined(__cplusplus) && __cplusplus >= 201103L
#define BUILD_ASSERT(EXPR) static_assert(EXPR, "assertion failed")
#define BUILD_ASSERT_DECL(EXPR) static_assert(EXPR, "assertion failed")
#elif defined(__cplusplus) && __cplusplus < 201103L
#include <boost/static_assert.hpp>
#define BUILD_ASSERT BOOST_STATIC_ASSERT
#define BUILD_ASSERT_DECL BOOST_STATIC_ASSERT
#elif (__GNUC__ * 256 + __GNUC_MINOR__ >= 0x403 \
       || __has_extension(c_static_assert))
#define BUILD_ASSERT_DECL(EXPR) _Static_assert(EXPR, #EXPR)
#define BUILD_ASSERT(EXPR) (void) ({ _Static_assert(EXPR, #EXPR); })
#else
#define BUILD_ASSERT__(EXPR) \
        sizeof(struct { unsigned int build_assert_failed : (EXPR) ? 1 : -1; })
#define BUILD_ASSERT(EXPR) (void) BUILD_ASSERT__(EXPR)
#define BUILD_ASSERT_DECL(EXPR) \
        extern int (*build_assert(void))[BUILD_ASSERT__(EXPR)]
#endif

#ifdef __GNUC__
#define BUILD_ASSERT_GCCONLY(EXPR) BUILD_ASSERT(EXPR)
#define BUILD_ASSERT_DECL_GCCONLY(EXPR) BUILD_ASSERT_DECL(EXPR)
#else
#define BUILD_ASSERT_GCCONLY(EXPR) ((void) 0)
#define BUILD_ASSERT_DECL_GCCONLY(EXPR) ((void) 0)
#endif


#endif /* compiler.h */