/* * Copyright (C) 2014 Freie Universität Berlin * 2017 HAW-Hamburg * * This file is subject to the terms and conditions of the GNU Lesser * General Public License v2.1. See the file LICENSE in the top level * directory for more details. */ /** * @ingroup core_internal * @{ * * @file * @brief Common macros and compiler attributes/pragmas configuration * * @author René Kijewski * @author Michel Rottleuthner */ #ifndef KERNEL_DEFINES_H #define KERNEL_DEFINES_H #include #include #ifdef __cplusplus extern "C" { #endif /* uncrustify gets mightily confused by these macros... */ /* begin{code-style-ignore} */ /** * @def container_of(PTR, TYPE, MEMBER) * @brief Returns the container of a pointer to a member. * @details For a struct `TYPE` with a member `MEMBER`, * given a pointer `PTR` to `TYPE::MEMBER` this function returns a pointer * to the instance of `TYPE`. * @details E.g. for `struct my_struct_t { ...; something_t n; ... } my_struct;`, * `&my_struct == container_of(&my_struct.n, struct my_struct_t, n)`. * @param[in] PTR pointer to a member * @param[in] TYPE a type name (a struct or union), container of PTR * @param[in] MEMBER name of the member of TYPE which PTR points to * @return Pointer to the container of PTR. */ #if __STDC_VERSION__ >= 201112L # define container_of(PTR, TYPE, MEMBER) \ (_Generic((PTR), \ const __typeof__ (((TYPE *) 0)->MEMBER) *: \ ((TYPE *) ((uintptr_t) (PTR) - offsetof(TYPE, MEMBER))), \ __typeof__ (((TYPE *) 0)->MEMBER) *: \ ((TYPE *) ((uintptr_t) (PTR) - offsetof(TYPE, MEMBER))) \ )) #elif defined __GNUC__ # define container_of(PTR, TYPE, MEMBER) \ (__extension__ ({ \ __extension__ const __typeof__ (((TYPE *) 0)->MEMBER) *__m____ = (PTR); \ ((TYPE *) ((uintptr_t) __m____ - offsetof(TYPE, MEMBER))); \ })) #else # define container_of(PTR, TYPE, MEMBER) \ ((TYPE *) ((char *) (PTR) - offsetof(TYPE, MEMBER))) #endif /** * @def NORETURN * @brief The *NORETURN* keyword tells the compiler to assume that the function * cannot return. */ #ifdef __GNUC__ #define NORETURN __attribute__((noreturn)) #else #define NORETURN #endif /** * @def CONST * @brief A function declared as *CONST* is #PURE and also not allowed to * examine global memory. I.e. a *CONST* function cannot even * dereference a pointer parameter. */ #ifdef __GNUC__ #define CONST __attribute__((const)) #else #define CONST #endif /** * @def PURE * @brief The function has no effects except the return value and its return * value depends only on the parameters and/or global variables. Such a * function can be subject to common subexpression elimination and loop * optimization just as an arithmetic operator would be. */ #ifdef __GNUC__ #define PURE __attribute__((pure)) #else #define PURE #endif /** * @def UNREACHABLE() * @brief Tell the compiler that this line of code cannot be reached. * @details Most useful in junction with #NORETURN. * Use this if the compiler cannot tell that e.g. * an assembler instruction causes a longjmp, or a write causes a reboot. */ #if ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 5)) || (__GNUC__ >= 5) #define UNREACHABLE() __builtin_unreachable() #else #define UNREACHABLE() do { /* nothing */ } while (1) #endif /** * @def ARRAY_SIZE(a) * @brief Calculate the number of elements in a static array. * @param[in] a Array to examine * @returns The number of elements in the array a. */ #ifndef ARRAY_SIZE #define ARRAY_SIZE(a) (sizeof((a)) / sizeof((a)[0])) #endif /** * @def ALIGN_OF(T) * @brief Calculate the minimal alignment for type T. * @param[in] T Type to examine * @returns The minimal alignment of T. */ #define ALIGN_OF(T) (offsetof(struct { char c; T t; }, t)) /** * @def BUILD_BUG_ON(condition) * @brief Forces a compilation error if condition is true. * This trick is only needed if the condition can't be evaluated * before compile time (i.e. sizeof(sometype_t) < 42 ) * For more details on this see for example: * https://git.kernel.org/pub/scm/linux/kernel/git/stable/ * linux-stable.git/tree/include/linux/bug.h * @param[in] condition A condition that will be evaluated at compile time */ #define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2 * !!(condition)])) /** * @def IS_ACTIVE(macro) * @brief Allows to verify a macro definition outside the preprocessor. * * @details This macro is based on Linux's clever 'IS_BUILTIN' * (https://github.com/torvalds/linux/blob/master/include/linux/kconfig.h). * It takes a @p macro value that may be defined to 1 or not even * defined (e.g. FEATURE_FOO) and then expands it to an expression * that can be used in C code, either 1 or 0. * * The advantage of using this is that the compiler sees all the * code, so checks can be performed, sections that would not be * executed are removed during optimization. For example: * ``` * if (IS_ACTIVE(FEATURE_FOO)) { * do_something(); * } * ``` * @param[in] macro Macro to evaluate * @returns 1 if the macro is defined to 1 * @returns 0 if the macro is not defined, of if it is defined to something * else than 1. * * @note This should only be used when macros are defined as 1, it will * not work if the macro value is, for example, (1) or 1U. * * @note Although this may seem to work similarly to the preprocessor's * 'defined', it is not entirely equal. If the given macro has * been defined with no value, this will expand to 0. Also note * that this is intended to be used with 'boolean' macros that act * as switches, and usually will be defined as 1 or not defined. */ #define IS_ACTIVE(macro) __is_active(macro) /** * @def IS_USED(module) * @brief Checks whether a module is being used or not. Can be used in C * conditionals. * * @param[in] module Module to check * @returns 1 if the module is being used * @returns 0 if the module is not being used */ #define IS_USED(module) IS_ACTIVE(module) /** * @cond INTERNAL */ /* Here a prefix "__PREFIX_WHEN_" is added to the macro. So if it was a 1 we * have "__PREFIX_WHEN_1", and if it was not defined we have "__PREFIX_WHEN_". */ #define __is_active(val) ___is_active(__PREFIX_WHEN_##val) /* With this placeholder we turn the original value into two arguments when the * original value was defined as 1 (note the comma). */ #define __PREFIX_WHEN_1 0, /* Here we add two extra arguments, that way the next macro can accept varargs. * * If the original macro was defined as 1, this will have three arguments * (__take_second_arg(0, 1, 0, 0)), otherwise it will have two * (__take_second_arg(__PREFIX_WHEN_ 1, 0, 0)). The third zero is there just to * be compliant with C99, which states that when a function-like macro ends * with ellipsis (...) it should be called with at least one argument for the * variable list. */ #define ___is_active(arg1_or_junk) __take_second_arg(arg1_or_junk 1, 0, 0) /* Finally, we just always take the second argument, which will be either 1 * (when three arguments are passed, i.e. macro was defined as 1) or 0 (when * only two arguments are passed). */ #define __take_second_arg(__ignored, val, ...) val /** * @endcond */ /* end{code-style-ignore} */ #ifdef __cplusplus } #endif #endif /* KERNEL_DEFINES_H */ /** @} */